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444 lines
46 KiB
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<div class="body">
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<div class="section" id="id1">
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<h1>快速入门</h1>
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<div class="admonition note">
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<p class="first admonition-title">注解</p>
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<p class="last">译者注：编程名词和专业名词尽量不翻译，比如bands, modes等请参考 <tt class="xref doc docutils literal"><span class="pre">概念</span></tt> 。</p>
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</div>
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<div class="section" id="image">
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<h2>使用 Image 类</h2>
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<p>PIL最重要的类是
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<a class="reference internal" href="../reference/Image.html#PIL.Image.Image" title="PIL.Image.Image"><tt class="xref py py-class docutils literal"><span class="pre">Image</span></tt></a> class, 你可以通过多种方法创建这个类的实例；你可以从文件加载图像，或者处理其他图像, 或者从 scratch 创建。</p>
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<p>要从文件加载图像，使用 <a class="reference internal" href="../reference/Image.html#PIL.Image.open" title="PIL.Image.open"><tt class="xref py py-func docutils literal"><span class="pre">open()</span></tt></a> 函数，
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在 <a class="reference internal" href="../reference/Image.html#module-PIL.Image" title="PIL.Image"><tt class="xref py py-mod docutils literal"><span class="pre">Image</span></tt></a> 模块:</p>
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<div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="kn">from</span> <span class="nn">PIL</span> <span class="kn">import</span> <span class="n">Image</span>
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<span class="gp">>>> </span><span class="n">im</span> <span class="o">=</span> <span class="n">Image</span><span class="o">.</span><span class="n">open</span><span class="p">(</span><span class="s">"lena.ppm"</span><span class="p">)</span>
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</pre></div>
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</div>
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<p>加载成功将返回一个 <a class="reference internal" href="../reference/Image.html#PIL.Image.Image" title="PIL.Image.Image"><tt class="xref py py-class docutils literal"><span class="pre">Image</span></tt></a> 对象。
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你现在可以使用示例属性检查文件内容:</p>
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<div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="kn">from</span> <span class="nn">__future__</span> <span class="kn">import</span> <span class="n">print_function</span>
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<span class="gp">>>> </span><span class="k">print</span><span class="p">(</span><span class="n">im</span><span class="o">.</span><span class="n">format</span><span class="p">,</span> <span class="n">im</span><span class="o">.</span><span class="n">size</span><span class="p">,</span> <span class="n">im</span><span class="o">.</span><span class="n">mode</span><span class="p">)</span>
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<span class="go">PPM (512, 512) RGB</span>
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</pre></div>
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</div>
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<p><tt class="xref py py-attr docutils literal"><span class="pre">format</span></tt> 这个属性标识了图像来源。如果图像不是从文件读取它的值就是None。size属性是一个二元tuple，包含width和height（宽度和高度，单位都是px）。
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<tt class="xref py py-attr docutils literal"><span class="pre">mode</span></tt> 属性定义了图像bands的数量和名称，以及像素类型和深度。常见的modes 有 “L”
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(luminance) 表示灰度图像, “RGB” 表示真彩色图像, and “CMYK” 表示出版图像。</p>
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<p>如果文件打开错误，返回 <tt class="xref py py-exc docutils literal"><span class="pre">IOError</span></tt> 错误。</p>
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<p>只要你有了 <a class="reference internal" href="../reference/Image.html#PIL.Image.Image" title="PIL.Image.Image"><tt class="xref py py-class docutils literal"><span class="pre">Image</span></tt></a> 类的实例，你就可以通过类的方法处理图像。比如，下列方法可以显示图像:</p>
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<div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">im</span><span class="o">.</span><span class="n">show</span><span class="p">()</span>
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</pre></div>
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</div>
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<div class="admonition note">
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<p class="first admonition-title">注解</p>
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<p class="last">标准的 <a class="reference internal" href="../reference/Image.html#PIL.Image.Image.show" title="PIL.Image.Image.show"><tt class="xref py py-meth docutils literal"><span class="pre">show()</span></tt></a> 效率并不高，它需要保存图像到临时文件然后通过
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<strong class="command">xv</strong> 显示图像。你需要先安装 <strong class="command">xv</strong> ，显示图像有助于调试和测试。</p>
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</div>
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<p>下面的部分提供了这个库其他函数的概览。</p>
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</div>
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<div class="section" id="id2">
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<h2>读写图像</h2>
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<p>PIL 模块支持大量图片格式。使用在
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<a class="reference internal" href="../reference/Image.html#module-PIL.Image" title="PIL.Image"><tt class="xref py py-mod docutils literal"><span class="pre">Image</span></tt></a> 模块的 <a class="reference internal" href="../reference/Image.html#PIL.Image.open" title="PIL.Image.open"><tt class="xref py py-func docutils literal"><span class="pre">open()</span></tt></a> 函数从磁盘读取文件。你不需要知道文件格式就能打开它，这个库能够根据文件内容自动确定文件格式。</p>
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<p>要保存文件，使用
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<a class="reference internal" href="../reference/Image.html#PIL.Image.Image" title="PIL.Image.Image"><tt class="xref py py-class docutils literal"><span class="pre">Image</span></tt></a> 类的 <a class="reference internal" href="../reference/Image.html#PIL.Image.Image.save" title="PIL.Image.Image.save"><tt class="xref py py-meth docutils literal"><span class="pre">save()</span></tt></a> 方法。保存文件的时候文件名变得重要了。除非你指定格式，否则这个库将会以文件名的扩展名作为格式保存。</p>
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<div class="section" id="jpeg">
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<h3>转换文件格式到JPEG</h3>
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<div class="highlight-python"><div class="highlight"><pre><span class="kn">from</span> <span class="nn">__future__</span> <span class="kn">import</span> <span class="n">print_function</span>
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<span class="kn">import</span> <span class="nn">os</span><span class="o">,</span> <span class="nn">sys</span>
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<span class="kn">from</span> <span class="nn">PIL</span> <span class="kn">import</span> <span class="n">Image</span>
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<span class="k">for</span> <span class="n">infile</span> <span class="ow">in</span> <span class="n">sys</span><span class="o">.</span><span class="n">argv</span><span class="p">[</span><span class="mi">1</span><span class="p">:]:</span>
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<span class="n">f</span><span class="p">,</span> <span class="n">e</span> <span class="o">=</span> <span class="n">os</span><span class="o">.</span><span class="n">path</span><span class="o">.</span><span class="n">splitext</span><span class="p">(</span><span class="n">infile</span><span class="p">)</span>
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<span class="n">outfile</span> <span class="o">=</span> <span class="n">f</span> <span class="o">+</span> <span class="s">".jpg"</span>
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<span class="k">if</span> <span class="n">infile</span> <span class="o">!=</span> <span class="n">outfile</span><span class="p">:</span>
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<span class="k">try</span><span class="p">:</span>
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<span class="n">Image</span><span class="o">.</span><span class="n">open</span><span class="p">(</span><span class="n">infile</span><span class="p">)</span><span class="o">.</span><span class="n">save</span><span class="p">(</span><span class="n">outfile</span><span class="p">)</span>
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<span class="k">except</span> <span class="ne">IOError</span><span class="p">:</span>
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<span class="k">print</span><span class="p">(</span><span class="s">"cannot convert"</span><span class="p">,</span> <span class="n">infile</span><span class="p">)</span>
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</pre></div>
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</div>
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<p><a class="reference internal" href="../reference/Image.html#PIL.Image.Image.save" title="PIL.Image.Image.save"><tt class="xref py py-meth docutils literal"><span class="pre">save()</span></tt></a> 方法的第二个参数可以指定文件格式，如果你使用非标准的扩展名你必须这样做：</p>
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</div>
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<div class="section" id="id3">
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<h3>创建 JPEG 缩略图</h3>
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<div class="highlight-python"><div class="highlight"><pre><span class="kn">from</span> <span class="nn">__future__</span> <span class="kn">import</span> <span class="n">print_function</span>
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<span class="kn">import</span> <span class="nn">os</span><span class="o">,</span> <span class="nn">sys</span>
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<span class="kn">from</span> <span class="nn">PIL</span> <span class="kn">import</span> <span class="n">Image</span>
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<span class="n">size</span> <span class="o">=</span> <span class="p">(</span><span class="mi">128</span><span class="p">,</span> <span class="mi">128</span><span class="p">)</span>
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<span class="k">for</span> <span class="n">infile</span> <span class="ow">in</span> <span class="n">sys</span><span class="o">.</span><span class="n">argv</span><span class="p">[</span><span class="mi">1</span><span class="p">:]:</span>
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<span class="n">outfile</span> <span class="o">=</span> <span class="n">os</span><span class="o">.</span><span class="n">path</span><span class="o">.</span><span class="n">splitext</span><span class="p">(</span><span class="n">infile</span><span class="p">)[</span><span class="mi">0</span><span class="p">]</span> <span class="o">+</span> <span class="s">".thumbnail"</span>
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<span class="k">if</span> <span class="n">infile</span> <span class="o">!=</span> <span class="n">outfile</span><span class="p">:</span>
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<span class="k">try</span><span class="p">:</span>
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<span class="n">im</span> <span class="o">=</span> <span class="n">Image</span><span class="o">.</span><span class="n">open</span><span class="p">(</span><span class="n">infile</span><span class="p">)</span>
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<span class="n">im</span><span class="o">.</span><span class="n">thumbnail</span><span class="p">(</span><span class="n">size</span><span class="p">)</span>
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<span class="n">im</span><span class="o">.</span><span class="n">save</span><span class="p">(</span><span class="n">outfile</span><span class="p">,</span> <span class="s">"JPEG"</span><span class="p">)</span>
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<span class="k">except</span> <span class="ne">IOError</span><span class="p">:</span>
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<span class="k">print</span><span class="p">(</span><span class="s">"cannot create thumbnail for"</span><span class="p">,</span> <span class="n">infile</span><span class="p">)</span>
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</pre></div>
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</div>
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<p>很重要的一点是这个库不会直接解码或者加载图像栅格数据。当你打开一个文件，只会读取文件头信息用来确定格式，颜色模式，大小等等，文件的剩余部分不会主动处理。这意味着打开一个图像文件的操作十分快速，跟图片大小和压缩方式无关。下面是一个简单的脚本用来快速验证大量图片。</p>
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</div>
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<div class="section" id="id4">
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<h3>验证图像文件</h3>
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<div class="highlight-python"><div class="highlight"><pre><span class="kn">from</span> <span class="nn">__future__</span> <span class="kn">import</span> <span class="n">print_function</span>
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<span class="kn">import</span> <span class="nn">sys</span>
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<span class="kn">from</span> <span class="nn">PIL</span> <span class="kn">import</span> <span class="n">Image</span>
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<span class="k">for</span> <span class="n">infile</span> <span class="ow">in</span> <span class="n">sys</span><span class="o">.</span><span class="n">argv</span><span class="p">[</span><span class="mi">1</span><span class="p">:]:</span>
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<span class="k">try</span><span class="p">:</span>
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<span class="k">with</span> <span class="n">Image</span><span class="o">.</span><span class="n">open</span><span class="p">(</span><span class="n">infile</span><span class="p">)</span> <span class="k">as</span> <span class="n">im</span><span class="p">:</span>
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<span class="k">print</span><span class="p">(</span><span class="n">infile</span><span class="p">,</span> <span class="n">im</span><span class="o">.</span><span class="n">format</span><span class="p">,</span> <span class="s">"</span><span class="si">%d</span><span class="s">x</span><span class="si">%d</span><span class="s">"</span> <span class="o">%</span> <span class="n">im</span><span class="o">.</span><span class="n">size</span><span class="p">,</span> <span class="n">im</span><span class="o">.</span><span class="n">mode</span><span class="p">)</span>
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<span class="k">except</span> <span class="ne">IOError</span><span class="p">:</span>
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<span class="k">pass</span>
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</pre></div>
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</div>
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</div>
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</div>
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<div class="section" id="id5">
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<h2>剪切，粘贴，合并图像</h2>
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<p><a class="reference internal" href="../reference/Image.html#PIL.Image.Image" title="PIL.Image.Image"><tt class="xref py py-class docutils literal"><span class="pre">Image</span></tt></a> 类包含的方法允许你操作图像部分选区。使用:py:meth:<cite>~PIL.Image.Image.crop</cite> 方法获取图像的一个子矩形选区。</p>
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<div class="section" id="id6">
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<h3>从图像中复制出一个矩形选区</h3>
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<div class="highlight-python"><div class="highlight"><pre><span class="n">box</span> <span class="o">=</span> <span class="p">(</span><span class="mi">100</span><span class="p">,</span> <span class="mi">100</span><span class="p">,</span> <span class="mi">400</span><span class="p">,</span> <span class="mi">400</span><span class="p">)</span>
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<span class="n">region</span> <span class="o">=</span> <span class="n">im</span><span class="o">.</span><span class="n">crop</span><span class="p">(</span><span class="n">box</span><span class="p">)</span>
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</pre></div>
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</div>
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<p>矩形选区有一个4元元组定义，分别表示左、上、右、下的坐标。这个库以左上角为坐标原点，单位是px，所以上诉代码复制了一个 300x300 pixels 的矩形选区。这个选区现在可以被处理并且粘贴到原图。</p>
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</div>
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<div class="section" id="id7">
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<h3>处理复制的矩形选区并粘贴到原图</h3>
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<div class="highlight-python"><div class="highlight"><pre><span class="n">region</span> <span class="o">=</span> <span class="n">region</span><span class="o">.</span><span class="n">transpose</span><span class="p">(</span><span class="n">Image</span><span class="o">.</span><span class="n">ROTATE_180</span><span class="p">)</span>
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<span class="n">im</span><span class="o">.</span><span class="n">paste</span><span class="p">(</span><span class="n">region</span><span class="p">,</span> <span class="n">box</span><span class="p">)</span>
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</pre></div>
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</div>
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<p>当你粘贴矩形选区的时候必须保证尺寸一致。此外，矩形选区不能在图像外。然而你不必保证矩形选区和原图的颜色模式一致，因为矩形选区会被自动转换颜色（参看下面的 <a class="reference internal" href="#color-transforms"><em>颜色变换</em></a> 部分），下面是一个例子：</p>
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</div>
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<div class="section" id="rolling-an-image">
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<h3>Rolling an image</h3>
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<div class="highlight-python"><div class="highlight"><pre><span class="k">def</span> <span class="nf">roll</span><span class="p">(</span><span class="n">image</span><span class="p">,</span> <span class="n">delta</span><span class="p">):</span>
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<span class="s">"Roll an image sideways"</span>
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<span class="n">xsize</span><span class="p">,</span> <span class="n">ysize</span> <span class="o">=</span> <span class="n">image</span><span class="o">.</span><span class="n">size</span>
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<span class="n">delta</span> <span class="o">=</span> <span class="n">delta</span> <span class="o">%</span> <span class="n">xsize</span>
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<span class="k">if</span> <span class="n">delta</span> <span class="o">==</span> <span class="mi">0</span><span class="p">:</span> <span class="k">return</span> <span class="n">image</span>
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<span class="n">part1</span> <span class="o">=</span> <span class="n">image</span><span class="o">.</span><span class="n">crop</span><span class="p">((</span><span class="mi">0</span><span class="p">,</span> <span class="mi">0</span><span class="p">,</span> <span class="n">delta</span><span class="p">,</span> <span class="n">ysize</span><span class="p">))</span>
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<span class="n">part2</span> <span class="o">=</span> <span class="n">image</span><span class="o">.</span><span class="n">crop</span><span class="p">((</span><span class="n">delta</span><span class="p">,</span> <span class="mi">0</span><span class="p">,</span> <span class="n">xsize</span><span class="p">,</span> <span class="n">ysize</span><span class="p">))</span>
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<span class="n">image</span><span class="o">.</span><span class="n">paste</span><span class="p">(</span><span class="n">part2</span><span class="p">,</span> <span class="p">(</span><span class="mi">0</span><span class="p">,</span> <span class="mi">0</span><span class="p">,</span> <span class="n">xsize</span><span class="o">-</span><span class="n">delta</span><span class="p">,</span> <span class="n">ysize</span><span class="p">))</span>
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<span class="n">image</span><span class="o">.</span><span class="n">paste</span><span class="p">(</span><span class="n">part1</span><span class="p">,</span> <span class="p">(</span><span class="n">xsize</span><span class="o">-</span><span class="n">delta</span><span class="p">,</span> <span class="mi">0</span><span class="p">,</span> <span class="n">xsize</span><span class="p">,</span> <span class="n">ysize</span><span class="p">))</span>
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<span class="k">return</span> <span class="n">image</span>
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</pre></div>
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</div>
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<p>For more advanced tricks, the paste method can also take a transparency mask as
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an optional argument. In this mask, the value 255 indicates that the pasted
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image is opaque in that position (that is, the pasted image should be used as
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is). The value 0 means that the pasted image is completely transparent. Values
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in-between indicate different levels of transparency.</p>
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<p>The Python Imaging Library also allows you to work with the individual bands of
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an multi-band image, such as an RGB image. The split method creates a set of
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new images, each containing one band from the original multi-band image. The
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merge function takes a mode and a tuple of images, and combines them into a new
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image. The following sample swaps the three bands of an RGB image:</p>
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</div>
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<div class="section" id="id8">
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<h3>分离和合并颜色通道</h3>
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<div class="highlight-python"><div class="highlight"><pre><span class="n">r</span><span class="p">,</span> <span class="n">g</span><span class="p">,</span> <span class="n">b</span> <span class="o">=</span> <span class="n">im</span><span class="o">.</span><span class="n">split</span><span class="p">()</span>
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<span class="n">im</span> <span class="o">=</span> <span class="n">Image</span><span class="o">.</span><span class="n">merge</span><span class="p">(</span><span class="s">"RGB"</span><span class="p">,</span> <span class="p">(</span><span class="n">b</span><span class="p">,</span> <span class="n">g</span><span class="p">,</span> <span class="n">r</span><span class="p">))</span>
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</pre></div>
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</div>
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<p>Note that for a single-band image, <a class="reference internal" href="../reference/Image.html#PIL.Image.Image.split" title="PIL.Image.Image.split"><tt class="xref py py-meth docutils literal"><span class="pre">split()</span></tt></a> returns
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the image itself. To work with individual color bands, you may want to convert
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the image to “RGB” first.</p>
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</div>
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</div>
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<div class="section" id="id9">
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<h2>几何变换</h2>
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<p>The <a class="reference internal" href="../reference/Image.html#PIL.Image.Image" title="PIL.Image.Image"><tt class="xref py py-class docutils literal"><span class="pre">PIL.Image.Image</span></tt></a> class contains methods to
|
||
<a class="reference internal" href="../reference/Image.html#PIL.Image.Image.resize" title="PIL.Image.Image.resize"><tt class="xref py py-meth docutils literal"><span class="pre">resize()</span></tt></a> and <a class="reference internal" href="../reference/Image.html#PIL.Image.Image.rotate" title="PIL.Image.Image.rotate"><tt class="xref py py-meth docutils literal"><span class="pre">rotate()</span></tt></a> an
|
||
image. The former takes a tuple giving the new size, the latter the angle in
|
||
degrees counter-clockwise.</p>
|
||
<div class="section" id="id10">
|
||
<h3>简单的几何变换</h3>
|
||
<div class="highlight-python"><div class="highlight"><pre><span class="n">out</span> <span class="o">=</span> <span class="n">im</span><span class="o">.</span><span class="n">resize</span><span class="p">((</span><span class="mi">128</span><span class="p">,</span> <span class="mi">128</span><span class="p">))</span>
|
||
<span class="n">out</span> <span class="o">=</span> <span class="n">im</span><span class="o">.</span><span class="n">rotate</span><span class="p">(</span><span class="mi">45</span><span class="p">)</span> <span class="c"># degrees counter-clockwise</span>
|
||
</pre></div>
|
||
</div>
|
||
<p>To rotate the image in 90 degree steps, you can either use the
|
||
<a class="reference internal" href="../reference/Image.html#PIL.Image.Image.rotate" title="PIL.Image.Image.rotate"><tt class="xref py py-meth docutils literal"><span class="pre">rotate()</span></tt></a> method or the
|
||
<a class="reference internal" href="../reference/Image.html#PIL.Image.Image.transpose" title="PIL.Image.Image.transpose"><tt class="xref py py-meth docutils literal"><span class="pre">transpose()</span></tt></a> method. The latter can also be used to
|
||
flip an image around its horizontal or vertical axis.</p>
|
||
</div>
|
||
<div class="section" id="id11">
|
||
<h3>旋转图像</h3>
|
||
<div class="highlight-python"><div class="highlight"><pre><span class="n">out</span> <span class="o">=</span> <span class="n">im</span><span class="o">.</span><span class="n">transpose</span><span class="p">(</span><span class="n">Image</span><span class="o">.</span><span class="n">FLIP_LEFT_RIGHT</span><span class="p">)</span>
|
||
<span class="n">out</span> <span class="o">=</span> <span class="n">im</span><span class="o">.</span><span class="n">transpose</span><span class="p">(</span><span class="n">Image</span><span class="o">.</span><span class="n">FLIP_TOP_BOTTOM</span><span class="p">)</span>
|
||
<span class="n">out</span> <span class="o">=</span> <span class="n">im</span><span class="o">.</span><span class="n">transpose</span><span class="p">(</span><span class="n">Image</span><span class="o">.</span><span class="n">ROTATE_90</span><span class="p">)</span>
|
||
<span class="n">out</span> <span class="o">=</span> <span class="n">im</span><span class="o">.</span><span class="n">transpose</span><span class="p">(</span><span class="n">Image</span><span class="o">.</span><span class="n">ROTATE_180</span><span class="p">)</span>
|
||
<span class="n">out</span> <span class="o">=</span> <span class="n">im</span><span class="o">.</span><span class="n">transpose</span><span class="p">(</span><span class="n">Image</span><span class="o">.</span><span class="n">ROTATE_270</span><span class="p">)</span>
|
||
</pre></div>
|
||
</div>
|
||
<p>There’s no difference in performance or result between <tt class="docutils literal"><span class="pre">transpose(ROTATE)</span></tt>
|
||
and corresponding <a class="reference internal" href="../reference/Image.html#PIL.Image.Image.rotate" title="PIL.Image.Image.rotate"><tt class="xref py py-meth docutils literal"><span class="pre">rotate()</span></tt></a> operations.</p>
|
||
<p>A more general form of image transformations can be carried out via the
|
||
<a class="reference internal" href="../reference/Image.html#PIL.Image.Image.transform" title="PIL.Image.Image.transform"><tt class="xref py py-meth docutils literal"><span class="pre">transform()</span></tt></a> method.</p>
|
||
</div>
|
||
</div>
|
||
<div class="section" id="color-transforms">
|
||
<span id="id12"></span><h2>颜色变换</h2>
|
||
<p>The Python Imaging Library allows you to convert images between different pixel
|
||
representations using the <a class="reference internal" href="../reference/Image.html#PIL.Image.Image.convert" title="PIL.Image.Image.convert"><tt class="xref py py-meth docutils literal"><span class="pre">convert()</span></tt></a> method.</p>
|
||
<div class="section" id="id13">
|
||
<h3>颜色模式转换</h3>
|
||
<div class="highlight-python"><div class="highlight"><pre><span class="n">im</span> <span class="o">=</span> <span class="n">Image</span><span class="o">.</span><span class="n">open</span><span class="p">(</span><span class="s">"lena.ppm"</span><span class="p">)</span><span class="o">.</span><span class="n">convert</span><span class="p">(</span><span class="s">"L"</span><span class="p">)</span>
|
||
</pre></div>
|
||
</div>
|
||
<p>The library supports transformations between each supported mode and the “L”
|
||
and “RGB” modes. To convert between other modes, you may have to use an
|
||
intermediate image (typically an “RGB” image).</p>
|
||
</div>
|
||
</div>
|
||
<div class="section" id="id14">
|
||
<h2>颜色增强</h2>
|
||
<p>The Python Imaging Library provides a number of methods and modules that can be
|
||
used to enhance images.</p>
|
||
<div class="section" id="id15">
|
||
<h3>过滤器</h3>
|
||
<p>The <a class="reference internal" href="../reference/ImageFilter.html#module-PIL.ImageFilter" title="PIL.ImageFilter"><tt class="xref py py-mod docutils literal"><span class="pre">ImageFilter</span></tt></a> module contains a number of pre-defined
|
||
enhancement filters that can be used with the
|
||
<a class="reference internal" href="../reference/Image.html#PIL.Image.Image.filter" title="PIL.Image.Image.filter"><tt class="xref py py-meth docutils literal"><span class="pre">filter()</span></tt></a> method.</p>
|
||
<div class="section" id="id16">
|
||
<h4>应用过滤器</h4>
|
||
<div class="highlight-python"><div class="highlight"><pre><span class="kn">from</span> <span class="nn">PIL</span> <span class="kn">import</span> <span class="n">ImageFilter</span>
|
||
<span class="n">out</span> <span class="o">=</span> <span class="n">im</span><span class="o">.</span><span class="n">filter</span><span class="p">(</span><span class="n">ImageFilter</span><span class="o">.</span><span class="n">DETAIL</span><span class="p">)</span>
|
||
</pre></div>
|
||
</div>
|
||
</div>
|
||
</div>
|
||
<div class="section" id="id17">
|
||
<h3>点操作</h3>
|
||
<p>The <a class="reference internal" href="../reference/Image.html#PIL.Image.Image.point" title="PIL.Image.Image.point"><tt class="xref py py-meth docutils literal"><span class="pre">point()</span></tt></a> method can be used to translate the pixel
|
||
values of an image (e.g. image contrast manipulation). In most cases, a
|
||
function object expecting one argument can be passed to the this method. Each
|
||
pixel is processed according to that function:</p>
|
||
<div class="section" id="id18">
|
||
<h4>应用点操作</h4>
|
||
<div class="highlight-python"><div class="highlight"><pre><span class="c"># multiply each pixel by 1.2</span>
|
||
<span class="n">out</span> <span class="o">=</span> <span class="n">im</span><span class="o">.</span><span class="n">point</span><span class="p">(</span><span class="k">lambda</span> <span class="n">i</span><span class="p">:</span> <span class="n">i</span> <span class="o">*</span> <span class="mf">1.2</span><span class="p">)</span>
|
||
</pre></div>
|
||
</div>
|
||
<p>Using the above technique, you can quickly apply any simple expression to an
|
||
image. You can also combine the <a class="reference internal" href="../reference/Image.html#PIL.Image.Image.point" title="PIL.Image.Image.point"><tt class="xref py py-meth docutils literal"><span class="pre">point()</span></tt></a> and
|
||
<a class="reference internal" href="../reference/Image.html#PIL.Image.Image.paste" title="PIL.Image.Image.paste"><tt class="xref py py-meth docutils literal"><span class="pre">paste()</span></tt></a> methods to selectively modify an image:</p>
|
||
</div>
|
||
<div class="section" id="bands">
|
||
<h4>处理个别bands</h4>
|
||
<div class="highlight-python"><div class="highlight"><pre><span class="c"># split the image into individual bands</span>
|
||
<span class="n">source</span> <span class="o">=</span> <span class="n">im</span><span class="o">.</span><span class="n">split</span><span class="p">()</span>
|
||
|
||
<span class="n">R</span><span class="p">,</span> <span class="n">G</span><span class="p">,</span> <span class="n">B</span> <span class="o">=</span> <span class="mi">0</span><span class="p">,</span> <span class="mi">1</span><span class="p">,</span> <span class="mi">2</span>
|
||
|
||
<span class="c"># select regions where red is less than 100</span>
|
||
<span class="n">mask</span> <span class="o">=</span> <span class="n">source</span><span class="p">[</span><span class="n">R</span><span class="p">]</span><span class="o">.</span><span class="n">point</span><span class="p">(</span><span class="k">lambda</span> <span class="n">i</span><span class="p">:</span> <span class="n">i</span> <span class="o"><</span> <span class="mi">100</span> <span class="ow">and</span> <span class="mi">255</span><span class="p">)</span>
|
||
|
||
<span class="c"># process the green band</span>
|
||
<span class="n">out</span> <span class="o">=</span> <span class="n">source</span><span class="p">[</span><span class="n">G</span><span class="p">]</span><span class="o">.</span><span class="n">point</span><span class="p">(</span><span class="k">lambda</span> <span class="n">i</span><span class="p">:</span> <span class="n">i</span> <span class="o">*</span> <span class="mf">0.7</span><span class="p">)</span>
|
||
|
||
<span class="c"># paste the processed band back, but only where red was < 100</span>
|
||
<span class="n">source</span><span class="p">[</span><span class="n">G</span><span class="p">]</span><span class="o">.</span><span class="n">paste</span><span class="p">(</span><span class="n">out</span><span class="p">,</span> <span class="bp">None</span><span class="p">,</span> <span class="n">mask</span><span class="p">)</span>
|
||
|
||
<span class="c"># build a new multiband image</span>
|
||
<span class="n">im</span> <span class="o">=</span> <span class="n">Image</span><span class="o">.</span><span class="n">merge</span><span class="p">(</span><span class="n">im</span><span class="o">.</span><span class="n">mode</span><span class="p">,</span> <span class="n">source</span><span class="p">)</span>
|
||
</pre></div>
|
||
</div>
|
||
<p>Note the syntax used to create the mask:</p>
|
||
<div class="highlight-python"><div class="highlight"><pre><span class="n">imout</span> <span class="o">=</span> <span class="n">im</span><span class="o">.</span><span class="n">point</span><span class="p">(</span><span class="k">lambda</span> <span class="n">i</span><span class="p">:</span> <span class="n">expression</span> <span class="ow">and</span> <span class="mi">255</span><span class="p">)</span>
|
||
</pre></div>
|
||
</div>
|
||
<p>Python only evaluates the portion of a logical expression as is necessary to
|
||
determine the outcome, and returns the last value examined as the result of the
|
||
expression. So if the expression above is false (0), Python does not look at
|
||
the second operand, and thus returns 0. Otherwise, it returns 255.</p>
|
||
</div>
|
||
</div>
|
||
<div class="section" id="id19">
|
||
<h3>增强</h3>
|
||
<p>For more advanced image enhancement, you can use the classes in the
|
||
<a class="reference internal" href="../reference/ImageEnhance.html#module-PIL.ImageEnhance" title="PIL.ImageEnhance"><tt class="xref py py-mod docutils literal"><span class="pre">ImageEnhance</span></tt></a> module. Once created from an image, an enhancement
|
||
object can be used to quickly try out different settings.</p>
|
||
<p>You can adjust contrast, brightness, color balance and sharpness in this way.</p>
|
||
<div class="section" id="id20">
|
||
<h4>增强图形</h4>
|
||
<div class="highlight-python"><div class="highlight"><pre><span class="kn">from</span> <span class="nn">PIL</span> <span class="kn">import</span> <span class="n">ImageEnhance</span>
|
||
|
||
<span class="n">enh</span> <span class="o">=</span> <span class="n">ImageEnhance</span><span class="o">.</span><span class="n">Contrast</span><span class="p">(</span><span class="n">im</span><span class="p">)</span>
|
||
<span class="n">enh</span><span class="o">.</span><span class="n">enhance</span><span class="p">(</span><span class="mf">1.3</span><span class="p">)</span><span class="o">.</span><span class="n">show</span><span class="p">(</span><span class="s">"30% more contrast"</span><span class="p">)</span>
|
||
</pre></div>
|
||
</div>
|
||
</div>
|
||
</div>
|
||
</div>
|
||
<div class="section" id="id21">
|
||
<h2>多帧图像序列</h2>
|
||
<p>The Python Imaging Library contains some basic support for image sequences
|
||
(also called animation formats). Supported sequence formats include FLI/FLC,
|
||
GIF, and a few experimental formats. TIFF files can also contain more than one
|
||
frame.</p>
|
||
<p>When you open a sequence file, PIL automatically loads the first frame in the
|
||
sequence. You can use the seek and tell methods to move between different
|
||
frames:</p>
|
||
<div class="section" id="id22">
|
||
<h3>读取序列</h3>
|
||
<div class="highlight-python"><div class="highlight"><pre><span class="kn">from</span> <span class="nn">PIL</span> <span class="kn">import</span> <span class="n">Image</span>
|
||
|
||
<span class="n">im</span> <span class="o">=</span> <span class="n">Image</span><span class="o">.</span><span class="n">open</span><span class="p">(</span><span class="s">"animation.gif"</span><span class="p">)</span>
|
||
<span class="n">im</span><span class="o">.</span><span class="n">seek</span><span class="p">(</span><span class="mi">1</span><span class="p">)</span> <span class="c"># skip to the second frame</span>
|
||
|
||
<span class="k">try</span><span class="p">:</span>
|
||
<span class="k">while</span> <span class="mi">1</span><span class="p">:</span>
|
||
<span class="n">im</span><span class="o">.</span><span class="n">seek</span><span class="p">(</span><span class="n">im</span><span class="o">.</span><span class="n">tell</span><span class="p">()</span><span class="o">+</span><span class="mi">1</span><span class="p">)</span>
|
||
<span class="c"># do something to im</span>
|
||
<span class="k">except</span> <span class="ne">EOFError</span><span class="p">:</span>
|
||
<span class="k">pass</span> <span class="c"># end of sequence</span>
|
||
</pre></div>
|
||
</div>
|
||
<p>As seen in this example, you’ll get an <tt class="xref py py-exc docutils literal"><span class="pre">EOFError</span></tt> exception when the
|
||
sequence ends.</p>
|
||
<p>Note that most drivers in the current version of the library only allow you to
|
||
seek to the next frame (as in the above example). To rewind the file, you may
|
||
have to reopen it.</p>
|
||
<p>The following iterator class lets you to use the for-statement to loop over the
|
||
sequence:</p>
|
||
</div>
|
||
<div class="section" id="class">
|
||
<h3>序列迭代 class</h3>
|
||
<div class="highlight-python"><pre>class ImageSequence:
|
||
def __init__(self, im):
|
||
self.im = im
|
||
def __getitem__(self, ix):
|
||
try:
|
||
if ix:
|
||
self.im.seek(ix)
|
||
return self.im
|
||
except EOFError:
|
||
raise IndexError # end of sequence
|
||
|
||
for frame in ImageSequence(im):
|
||
# ...do something to frame...</pre>
|
||
</div>
|
||
</div>
|
||
</div>
|
||
<div class="section" id="postscript">
|
||
<h2>Postscript 打印</h2>
|
||
<p>The Python Imaging Library includes functions to print images, text and
|
||
graphics on Postscript printers. Here’s a simple example:</p>
|
||
<div class="section" id="drawing-postscript">
|
||
<h3>Drawing Postscript</h3>
|
||
<div class="highlight-python"><div class="highlight"><pre><span class="kn">from</span> <span class="nn">PIL</span> <span class="kn">import</span> <span class="n">Image</span>
|
||
<span class="kn">from</span> <span class="nn">PIL</span> <span class="kn">import</span> <span class="n">PSDraw</span>
|
||
|
||
<span class="n">im</span> <span class="o">=</span> <span class="n">Image</span><span class="o">.</span><span class="n">open</span><span class="p">(</span><span class="s">"lena.ppm"</span><span class="p">)</span>
|
||
<span class="n">title</span> <span class="o">=</span> <span class="s">"lena"</span>
|
||
<span class="n">box</span> <span class="o">=</span> <span class="p">(</span><span class="mi">1</span><span class="o">*</span><span class="mi">72</span><span class="p">,</span> <span class="mi">2</span><span class="o">*</span><span class="mi">72</span><span class="p">,</span> <span class="mi">7</span><span class="o">*</span><span class="mi">72</span><span class="p">,</span> <span class="mi">10</span><span class="o">*</span><span class="mi">72</span><span class="p">)</span> <span class="c"># in points</span>
|
||
|
||
<span class="n">ps</span> <span class="o">=</span> <span class="n">PSDraw</span><span class="o">.</span><span class="n">PSDraw</span><span class="p">()</span> <span class="c"># default is sys.stdout</span>
|
||
<span class="n">ps</span><span class="o">.</span><span class="n">begin_document</span><span class="p">(</span><span class="n">title</span><span class="p">)</span>
|
||
|
||
<span class="c"># draw the image (75 dpi)</span>
|
||
<span class="n">ps</span><span class="o">.</span><span class="n">image</span><span class="p">(</span><span class="n">box</span><span class="p">,</span> <span class="n">im</span><span class="p">,</span> <span class="mi">75</span><span class="p">)</span>
|
||
<span class="n">ps</span><span class="o">.</span><span class="n">rectangle</span><span class="p">(</span><span class="n">box</span><span class="p">)</span>
|
||
|
||
<span class="c"># draw centered title</span>
|
||
<span class="n">ps</span><span class="o">.</span><span class="n">setfont</span><span class="p">(</span><span class="s">"HelveticaNarrow-Bold"</span><span class="p">,</span> <span class="mi">36</span><span class="p">)</span>
|
||
<span class="n">w</span><span class="p">,</span> <span class="n">h</span><span class="p">,</span> <span class="n">b</span> <span class="o">=</span> <span class="n">ps</span><span class="o">.</span><span class="n">textsize</span><span class="p">(</span><span class="n">title</span><span class="p">)</span>
|
||
<span class="n">ps</span><span class="o">.</span><span class="n">text</span><span class="p">((</span><span class="mi">4</span><span class="o">*</span><span class="mi">72</span><span class="o">-</span><span class="n">w</span><span class="o">/</span><span class="mi">2</span><span class="p">,</span> <span class="mi">1</span><span class="o">*</span><span class="mi">72</span><span class="o">-</span><span class="n">h</span><span class="p">),</span> <span class="n">title</span><span class="p">)</span>
|
||
|
||
<span class="n">ps</span><span class="o">.</span><span class="n">end_document</span><span class="p">()</span>
|
||
</pre></div>
|
||
</div>
|
||
</div>
|
||
</div>
|
||
<div class="section" id="id23">
|
||
<h2>更多关于读取图像</h2>
|
||
<p>As described earlier, the <a class="reference internal" href="../reference/Image.html#PIL.Image.open" title="PIL.Image.open"><tt class="xref py py-func docutils literal"><span class="pre">open()</span></tt></a> function of the
|
||
<a class="reference internal" href="../reference/Image.html#module-PIL.Image" title="PIL.Image"><tt class="xref py py-mod docutils literal"><span class="pre">Image</span></tt></a> module is used to open an image file. In most cases, you
|
||
simply pass it the filename as an argument:</p>
|
||
<div class="highlight-python"><div class="highlight"><pre><span class="n">im</span> <span class="o">=</span> <span class="n">Image</span><span class="o">.</span><span class="n">open</span><span class="p">(</span><span class="s">"lena.ppm"</span><span class="p">)</span>
|
||
</pre></div>
|
||
</div>
|
||
<p>If everything goes well, the result is an <a class="reference internal" href="../reference/Image.html#PIL.Image.Image" title="PIL.Image.Image"><tt class="xref py py-class docutils literal"><span class="pre">PIL.Image.Image</span></tt></a> object.
|
||
Otherwise, an <tt class="xref py py-exc docutils literal"><span class="pre">IOError</span></tt> exception is raised.</p>
|
||
<p>You can use a file-like object instead of the filename. The object must
|
||
implement <a class="reference external" href="http://docs.python.org/2/library/stdtypes.html#file.read" title="(in Python v2.7)"><tt class="xref py py-meth docutils literal"><span class="pre">read()</span></tt></a>, <a class="reference external" href="http://docs.python.org/2/library/stdtypes.html#file.seek" title="(in Python v2.7)"><tt class="xref py py-meth docutils literal"><span class="pre">seek()</span></tt></a> and
|
||
<a class="reference external" href="http://docs.python.org/2/library/stdtypes.html#file.tell" title="(in Python v2.7)"><tt class="xref py py-meth docutils literal"><span class="pre">tell()</span></tt></a> methods, and be opened in binary mode.</p>
|
||
<div class="section" id="id24">
|
||
<h3>从文件读取</h3>
|
||
<div class="highlight-python"><div class="highlight"><pre><span class="n">fp</span> <span class="o">=</span> <span class="nb">open</span><span class="p">(</span><span class="s">"lena.ppm"</span><span class="p">,</span> <span class="s">"rb"</span><span class="p">)</span>
|
||
<span class="n">im</span> <span class="o">=</span> <span class="n">Image</span><span class="o">.</span><span class="n">open</span><span class="p">(</span><span class="n">fp</span><span class="p">)</span>
|
||
</pre></div>
|
||
</div>
|
||
<p>To read an image from string data, use the <a class="reference external" href="http://docs.python.org/2/library/stringio.html#StringIO.StringIO" title="(in Python v2.7)"><tt class="xref py py-class docutils literal"><span class="pre">StringIO</span></tt></a>
|
||
class:</p>
|
||
</div>
|
||
<div class="section" id="string">
|
||
<h3>从 string 读取</h3>
|
||
<div class="highlight-python"><div class="highlight"><pre><span class="kn">import</span> <span class="nn">StringIO</span>
|
||
|
||
<span class="n">im</span> <span class="o">=</span> <span class="n">Image</span><span class="o">.</span><span class="n">open</span><span class="p">(</span><span class="n">StringIO</span><span class="o">.</span><span class="n">StringIO</span><span class="p">(</span><span class="nb">buffer</span><span class="p">))</span>
|
||
</pre></div>
|
||
</div>
|
||
<p>Note that the library rewinds the file (using <tt class="docutils literal"><span class="pre">seek(0)</span></tt>) before reading the
|
||
image header. In addition, seek will also be used when the image data is read
|
||
(by the load method). If the image file is embedded in a larger file, such as a
|
||
tar file, you can use the <a class="reference internal" href="../PIL.html#module-PIL.ContainerIO" title="PIL.ContainerIO"><tt class="xref py py-class docutils literal"><span class="pre">ContainerIO</span></tt></a> or
|
||
<a class="reference internal" href="../PIL.html#module-PIL.TarIO" title="PIL.TarIO"><tt class="xref py py-class docutils literal"><span class="pre">TarIO</span></tt></a> modules to access it.</p>
|
||
</div>
|
||
<div class="section" id="id25">
|
||
<h3>从压缩包读取</h3>
|
||
<div class="highlight-python"><div class="highlight"><pre><span class="kn">from</span> <span class="nn">PIL</span> <span class="kn">import</span> <span class="n">TarIO</span>
|
||
|
||
<span class="n">fp</span> <span class="o">=</span> <span class="n">TarIO</span><span class="o">.</span><span class="n">TarIO</span><span class="p">(</span><span class="s">"Imaging.tar"</span><span class="p">,</span> <span class="s">"Imaging/test/lena.ppm"</span><span class="p">)</span>
|
||
<span class="n">im</span> <span class="o">=</span> <span class="n">Image</span><span class="o">.</span><span class="n">open</span><span class="p">(</span><span class="n">fp</span><span class="p">)</span>
|
||
</pre></div>
|
||
</div>
|
||
</div>
|
||
</div>
|
||
<div class="section" id="id26">
|
||
<h2>控制解码器</h2>
|
||
<p>Some decoders allow you to manipulate the image while reading it from a file.
|
||
This can often be used to speed up decoding when creating thumbnails (when
|
||
speed is usually more important than quality) and printing to a monochrome
|
||
laser printer (when only a greyscale version of the image is needed).</p>
|
||
<p>The <a class="reference internal" href="../reference/Image.html#PIL.Image.Image.draft" title="PIL.Image.Image.draft"><tt class="xref py py-meth docutils literal"><span class="pre">draft()</span></tt></a> method manipulates an opened but not yet
|
||
loaded image so it as closely as possible matches the given mode and size. This
|
||
is done by reconfiguring the image decoder.</p>
|
||
<div class="section" id="reading-in-draft-mode">
|
||
<h3>Reading in draft mode</h3>
|
||
<div class="highlight-python"><div class="highlight"><pre><span class="kn">from</span> <span class="nn">__future__</span> <span class="kn">import</span> <span class="n">print_function</span>
|
||
<span class="n">im</span> <span class="o">=</span> <span class="n">Image</span><span class="o">.</span><span class="n">open</span><span class="p">(</span><span class="nb">file</span><span class="p">)</span>
|
||
<span class="k">print</span><span class="p">(</span><span class="s">"original ="</span><span class="p">,</span> <span class="n">im</span><span class="o">.</span><span class="n">mode</span><span class="p">,</span> <span class="n">im</span><span class="o">.</span><span class="n">size</span><span class="p">)</span>
|
||
|
||
<span class="n">im</span><span class="o">.</span><span class="n">draft</span><span class="p">(</span><span class="s">"L"</span><span class="p">,</span> <span class="p">(</span><span class="mi">100</span><span class="p">,</span> <span class="mi">100</span><span class="p">))</span>
|
||
<span class="k">print</span><span class="p">(</span><span class="s">"draft ="</span><span class="p">,</span> <span class="n">im</span><span class="o">.</span><span class="n">mode</span><span class="p">,</span> <span class="n">im</span><span class="o">.</span><span class="n">size</span><span class="p">)</span>
|
||
</pre></div>
|
||
</div>
|
||
<p>This prints something like:</p>
|
||
<div class="highlight-python"><div class="highlight"><pre><span class="n">original</span> <span class="o">=</span> <span class="n">RGB</span> <span class="p">(</span><span class="mi">512</span><span class="p">,</span> <span class="mi">512</span><span class="p">)</span>
|
||
<span class="n">draft</span> <span class="o">=</span> <span class="n">L</span> <span class="p">(</span><span class="mi">128</span><span class="p">,</span> <span class="mi">128</span><span class="p">)</span>
|
||
</pre></div>
|
||
</div>
|
||
<p>Note that the resulting image may not exactly match the requested mode and
|
||
size. To make sure that the image is not larger than the given size, use the
|
||
thumbnail method instead.</p>
|
||
</div>
|
||
</div>
|
||
</div>
|
||
|
||
|
||
</div> |