Android图片压缩几种方式总结

图片压缩在Android开发中很常见也很重要，防止图片的OOM也是压缩的重要原因。

首先看下Bitmap图片文件的大小的决定因素：

Bitmap所占用的内存 = 图片长度 x 图片宽度 x 一个像素点占用的字节数。3个参数，任意减少一个的值，就达到了压缩的效果。

接下来看下Bitmap图片的几种格式的特点：

ALPHA_8
表示8位Alpha位图,即A=8,一个像素点占用1个字节,它没有颜色,只有透明度
ARGB_4444
表示16位ARGB位图，即A=4,R=4,G=4,B=4,一个像素点占4+4+4+4=16位，2个字节
ARGB_8888
表示32位ARGB位图，即A=8,R=8,G=8,B=8,一个像素点占8+8+8+8=32位，4个字节
RGB_565
表示16位RGB位图,即R=5,G=6,B=5,它没有透明度,一个像素点占5+6+5=16位，2个字节

如果进行图片格式的压缩的话，一般情况下都是ARGB_8888转为RGB565进行压缩。

写了一个工具类，基本上列举了android上图片的几种基本压缩方式：

1.质量压缩

2.采样率压缩

3.尺寸压缩

4.Matrix压缩

5.图片格式的压缩，例如PNG和JPG保存后的图片大小是不同的

public class Utils { /** * 采样率压缩 * * @param bitmap * @param sampleSize 采样率为2的整数倍，非整数倍四舍五入，如4的话，就是原图的1/4 * @return 尺寸变化 */ public static Bitmap getBitmap(Bitmap bitmap, int sampleSize) { BitmapFactory.Options options = new BitmapFactory.Options(); options.inSampleSize = sampleSize; ByteArrayOutputStream baos = new ByteArrayOutputStream(); bitmap.compress(Bitmap.CompressFormat.JPEG, 100, baos); byte[] bytes = baos.toByteArray(); Bitmap bit = BitmapFactory.decodeByteArray(bytes, 0, bytes.length, options); Log.i("info", "图片大小：" + bit.getByteCount());//2665296 10661184 return bit; } /** * 图片质量压缩 * * @param bitmap * @param quality * @return 尺寸不变，质量变小 */ public static Bitmap compressByQuality(Bitmap bitmap, int quality) { ByteArrayOutputStream baos = new ByteArrayOutputStream(); bitmap.compress(Bitmap.CompressFormat.JPEG, quality, baos); byte[] bytes = baos.toByteArray(); Bitmap bit = BitmapFactory.decodeByteArray(bytes, 0, bytes.length); Log.i("info", "图片大小：" + bit.getByteCount());//10661184 return bit; } /** * 图片质量压缩 * * @param src * @param maxByteSize * @return */ public static Bitmap compressByQuality(Bitmap src, long maxByteSize) { ByteArrayOutputStream baos = new ByteArrayOutputStream(); int quality = 100; src.compress(Bitmap.CompressFormat.JPEG, quality, baos); while (baos.toByteArray().length > maxByteSize && quality > 0) { baos.reset(); src.compress(Bitmap.CompressFormat.JPEG, quality -= 5, baos); } if (quality < 0) return null; byte[] bytes = baos.toByteArray(); Bitmap bit = BitmapFactory.decodeByteArray(bytes, 0, bytes.length); return bit; } public static Bitmap compressByFormat(Bitmap bitmap, int format) { ByteArrayOutputStream baos = new ByteArrayOutputStream(); bitmap.compress(Bitmap.CompressFormat.JPEG, 100, baos); byte[] bytes = baos.toByteArray(); Bitmap bit = BitmapFactory.decodeByteArray(bytes, 0, bytes.length); Log.i("info", "图片大小：" + bit.getByteCount());//10661184 return bit; } /** * Matrix缩放 * * @param bitmap * @param scaleWidth * @param scaleHeight * @return 尺寸和大小变化 */ public static Bitmap getBitmapBySize(Bitmap bitmap, float scaleWidth, float scaleHeight) { Matrix matrix = new Matrix(); matrix.postScale(scaleWidth, scaleHeight); Bitmap bit = Bitmap.createBitmap(bitmap, 0, 0, bitmap.getWidth(), bitmap.getHeight(), matrix, false); Log.i("info", "图片大小：" + bit.getByteCount()); return bit; } /** * 按照图片格式配置压缩 * * @param path * @param config ALPHA_8,ARGB_4444,ARGB_8888,RGB_565; * @return RGB_565比ARGB_8888节省一半内存 */ public static Bitmap getBitmapByFormatConfig(String path, Bitmap.Config config) { BitmapFactory.Options options = new BitmapFactory.Options(); options.inPreferredConfig = config; Bitmap bitmap = BitmapFactory.decodeFile(path, options); Log.i("info", "图片大小：" + bitmap.getByteCount()); return bitmap; } /** * 指定大小缩放 * * @param bitmap * @param width * @param height * @return */ public static Bitmap getBitmapByScaleSize(Bitmap bitmap, int width, int height) { Bitmap bit = Bitmap.createScaledBitmap(bitmap, width, height, true); Log.i("info", "图片大小：" + bit.getByteCount()); return bit; } /** * 通过保存格式压缩 * * @param bitmap * @param format JPEG,PNG,WEBP * @return */ public static Bitmap getBitmapByFormat(Bitmap bitmap, Bitmap.CompressFormat format) { ByteArrayOutputStream baos = new ByteArrayOutputStream(); bitmap.compress(format, 100, baos); byte[] bytes = baos.toByteArray(); Bitmap bit = BitmapFactory.decodeByteArray(bytes, 0, bytes.length); Log.i("info", "图片大小：" + bit.getByteCount()); return bit; } /** * 文件加载压缩 * * @param filePath * @param inSampleSize * @return */ public static Bitmap getBitmap(String filePath, int inSampleSize) { BitmapFactory.Options options = new BitmapFactory.Options(); options.inJustDecodeBounds = true; BitmapFactory.decodeFile(filePath, options);//此时不耗费和占用内存 options.inSampleSize = inSampleSize; options.inJustDecodeBounds = false; return BitmapFactory.decodeFile(filePath, options); } public static Bitmap getBitmap(String filePath) { return BitmapFactory.decodeFile(filePath); } public static Bitmap view2Bitmap(View view) { if (view == null) return null; Bitmap ret = Bitmap.createBitmap(view.getWidth(), view.getHeight(), Bitmap.Config.ARGB_8888); Canvas canvas = new Canvas(ret); Drawable bgDrawable = view.getBackground(); if (bgDrawable != null) { bgDrawable.draw(canvas); } else { canvas.drawColor(Color.WHITE); } view.draw(canvas); return ret; } public static void saveBitmap(Bitmap bitmap) { File file = new File(Environment.getExternalStorageDirectory() + "/img.jpg"); try { FileOutputStream fileOutputStream = new FileOutputStream(file); bitmap.compress(Bitmap.CompressFormat.JPEG, 100, fileOutputStream); fileOutputStream.flush(); fileOutputStream.close(); } catch (FileNotFoundException e) { e.printStackTrace(); } catch (IOException e) { e.printStackTrace(); } } public static void saveBitmap(Bitmap bitmap,Bitmap.CompressFormat format) { File file = new File(Environment.getExternalStorageDirectory() + "/img.jpg"); try { FileOutputStream fileOutputStream = new FileOutputStream(file); bitmap.compress(format, 100, fileOutputStream); fileOutputStream.flush(); fileOutputStream.close(); } catch (FileNotFoundException e) { e.printStackTrace(); } catch (IOException e) { e.printStackTrace(); } } }

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