Android 之 图片压缩

来自 子墨博客 http://blog.csdn.net/elinavampire

从图片的压缩方式区分：质量压缩和尺寸压缩。

质量压缩是在保持像素的前提下改变图片的位深及透明度等，来达到压缩图片的目的，经过它压缩的图片文件大小会有改变，但是导入成bitmap后占得内存是不变的。因为要保持像素不变，所以它就无法无限压缩，到达一个值之后就不会继续变小了。显然这个方法并不适用与缩略图，其实也不适用于想通过压缩图片减少内存的适用，仅仅适用于想在保证图片质量的同时减少文件大小的情况而已

尺寸压缩是压缩图片的像素，一张图片所占内存的大小 图片类型＊宽＊高，通过改变三个值减小图片所占的内存，防止OOM，当然这种方式可能会使图片失真

质量压缩：

<code class="hljs cs has-numbering"><span class="hljs-keyword">public</span> Bitmap <span class="hljs-title">compressImage</span>(Bitmap image，<span class="hljs-keyword">int</span> imageSize) {          ByteArrayOutputStream baos = <span class="hljs-keyword">new</span> ByteArrayOutputStream();          image.compress(Bitmap.CompressFormat.JPEG, <span class="hljs-number">100</span>, baos);<span class="hljs-comment">//质量压缩方法，这里100表示不压缩，把压缩后的数据存放到baos中  </span>        <span class="hljs-keyword">int</span> options = <span class="hljs-number">100</span>;          <span class="hljs-keyword">while</span> ( baos.toByteArray().length / <span class="hljs-number">1024</span>>imageSize) {  <span class="hljs-comment">//循环判断如果压缩后图片是否大于100kb,大于继续压缩         </span>            baos.reset();<span class="hljs-comment">//重置baos即清空baos  </span>            image.compress(Bitmap.CompressFormat.JPEG, options, baos);<span class="hljs-comment">//这里压缩options%，把压缩后的数据存放到baos中  </span>            options -= <span class="hljs-number">10</span>;<span class="hljs-comment">//每次都减少10  </span>        }          ByteArrayInputStream isBm = <span class="hljs-keyword">new</span> ByteArrayInputStream(baos.toByteArray());<span class="hljs-comment">//把压缩后的数据baos存放到ByteArrayInputStream中  </span>        Bitmap bitmap = BitmapFactory.decodeStream(isBm, <span class="hljs-keyword">null</span>, <span class="hljs-keyword">null</span>);<span class="hljs-comment">//把ByteArrayInputStream数据生成图片  </span>        <span class="hljs-keyword">return</span> bitmap;      } </code><ul style="display: block;" class="pre-numbering"><li>1</li><li>2</li><li>3</li><li>4</li><li>5</li><li>6</li><li>7</li><li>8</li><li>9</li><li>10</li><li>11</li><li>12</li><li>13</li><li>14</li></ul>

尺寸压缩：

<code class="hljs avrasm has-numbering">public void scalePic(int reqWidth,int reqHeight) {        BitmapFactory<span class="hljs-preprocessor">.Options</span> options = new BitmapFactory<span class="hljs-preprocessor">.Options</span>()<span class="hljs-comment">;</span>        options<span class="hljs-preprocessor">.inJustDecodeBounds</span> = true<span class="hljs-comment">;</span>        BitmapFactory<span class="hljs-preprocessor">.decodeResource</span>(getResources(), R<span class="hljs-preprocessor">.mipmap</span><span class="hljs-preprocessor">.demo</span>, options)<span class="hljs-comment">;</span>        options<span class="hljs-preprocessor">.inSampleSize</span> = PhotoUtil<span class="hljs-preprocessor">.calculateInSampleSize</span>(options, reqWidth,reqHeight)<span class="hljs-comment">;</span>        options<span class="hljs-preprocessor">.inJustDecodeBounds</span> = false<span class="hljs-comment">;</span>        bitmap = BitmapFactory<span class="hljs-preprocessor">.decodeResource</span>(getResources(), R<span class="hljs-preprocessor">.mipmap</span><span class="hljs-preprocessor">.demo</span>, options)<span class="hljs-comment">;</span>        postInvalidate()<span class="hljs-comment">;</span>    }</code><ul style="display: block;" class="pre-numbering"><li>1</li><li>2</li><li>3</li><li>4</li><li>5</li><li>6</li><li>7</li><li>8</li><li>9</li><li>10</li></ul>

<code class="hljs java has-numbering"><span class="hljs-keyword">public</span> <span class="hljs-keyword">static</span> <span class="hljs-keyword">int</span> <span class="hljs-title">calculateInSampleSize</span>(BitmapFactory.Options options,<span class="hljs-keyword">int</span> reqWidth, <span class="hljs-keyword">int</span> reqHeight) {        <span class="hljs-keyword">final</span> <span class="hljs-keyword">int</span> height = options.outHeight;        <span class="hljs-keyword">final</span> <span class="hljs-keyword">int</span> width = options.outWidth;        <span class="hljs-keyword">int</span> inSampleSize = <span class="hljs-number">1</span>;        <span class="hljs-keyword">if</span> (height > reqHeight || width > reqWidth) {            <span class="hljs-keyword">final</span> <span class="hljs-keyword">int</span> heightRatio = Math.round((<span class="hljs-keyword">float</span>) height / (<span class="hljs-keyword">float</span>) reqHeight);            <span class="hljs-keyword">final</span> <span class="hljs-keyword">int</span> widthRatio = Math.round((<span class="hljs-keyword">float</span>) width / (<span class="hljs-keyword">float</span>) reqWidth);            inSampleSize = heightRatio < widthRatio ? heightRatio : widthRatio;        }        <span class="hljs-keyword">return</span> inSampleSize;    }</code><ul style="display: block;" class="pre-numbering"><li>1</li><li>2</li><li>3</li><li>4</li><li>5</li><li>6</li><li>7</li><li>8</li><li>9</li><li>10</li><li>11</li></ul>

根据具体需求也可以两种压缩方式结合使用