Bitmap压缩用到的场景：{
1.移动端上传文件需要对本地拍摄保存的文件压缩：图片的缩放比例换算 大小的压缩
2.加载本地图片显示View位图所需要的图片大小并没有那么大
3.图片缓存：请求服务器上的资源缓存到内存或者本地存储提高缓存加载速率
}Bitmap缓存的优点：1.减少内存开销读取和存储更快 2.提高App流畅度
1.采样率压缩：
BitmapFactory.Options options = new BitmapFactory.Options(); //获取Bitmap工厂类
options.inJustDecodeBounds = true; //true 只返回Bitmap宽高 false 返回Bitmap对象实体
BitmapFactory.decodeFile(fileUrl, options);
int width = options.outWidth;
int height = options.outHeight;
int inSampleSize = 1; //采样率:采样率以1/2++ 形式换算
//根据输入的宽高换算采样率
if (height > outHeight || width > outWith) {
final int halfHeight = height / 2;
final int halfWidth = width / 2;
while ((halfHeight / inSampleSize) >= outHeight &&
(halfWidth / inSampleSize) >= outWith) {
inSampleSize *= 2;
}
}
2.质量压缩：
//进行有损压缩
ByteArrayOutputStream baos = new ByteArrayOutputStream();
int options_ = 100;
actualOutBitmap.compress(Bitmap.CompressFormat.JPEG, options_, baos);//质量压缩方法，把压缩后的数据存放到baos中 (100表示不压缩，0表示压缩到最小)
int baosLength = baos.toByteArray().length;
while (baosLength / 1024 > maxFileSize) {//循环判断如果压缩后图片是否大于maxMemmorrySize,大于继续压缩
baos.reset();//重置baos即让下一次的写入覆盖之前的内容
options_ = Math.max(0, options_ - 10);//图片质量每次减少10
actualOutBitmap.compress(Bitmap.CompressFormat.JPEG, options_, baos);//将压缩后的图片保存到baos中
baosLength = baos.toByteArray().length;
if (options_ == 0)//如果图片的质量已降到最低则，不再进行压缩
break;
}
actualOutBitmap.recycle();
3.缩放法压缩
/**
* Creates a new bitmap, scaled from an existing bitmap, when possible. If the
* specified width and height are the same as the current width and height of
* the source bitmap, the source bitmap is returned and no new bitmap is
* created.
*
* @param src The source bitmap.
* @param dstWidth The new bitmap's desired width.
* @param dstHeight The new bitmap's desired height.
* @param filter true if the source should be filtered.
* @return The new scaled bitmap or the source bitmap if no scaling is required.
* @throws IllegalArgumentException if width is <= 0, or height is <= 0
*/
public static Bitmap createScaledBitmap(@NonNull Bitmap src, int dstWidth, int dstHeight,
boolean filter) {
Matrix m = new Matrix();
//换算缩放比例
final int width = src.getWidth();
final int height = src.getHeight();
if (width != dstWidth || height != dstHeight) {
final float sx = dstWidth / (float) width;
final float sy = dstHeight / (float) height;
m.setScale(sx, sy);
}
return Bitmap.createBitmap(src, 0, 0, width, height, m, filter);
}
/**
* Returns an immutable bitmap from subset of the source bitmap,
* transformed by the optional matrix. The new bitmap may be the
* same object as source, or a copy may have been made. It is
* initialized with the same density and color space as the original
* bitmap.
*
* If the source bitmap is immutable and the requested subset is the
* same as the source bitmap itself, then the source bitmap is
* returned and no new bitmap is created.
*
* @param source The bitmap we are subsetting
* @param x The x coordinate of the first pixel in source
* @param y The y coordinate of the first pixel in source
* @param width The number of pixels in each row
* @param height The number of rows
* @param m Optional matrix to be applied to the pixels //设置缩放比例
* @param filter true if the source should be filtered.
* Only applies if the matrix contains more than just
* translation.
* @return A bitmap that represents the specified subset of source
* @throws IllegalArgumentException if the x, y, width, height values are
* outside of the dimensions of the source bitmap, or width is <= 0,
* or height is <= 0
*/
public static Bitmap createBitmap(@NonNull Bitmap source, int x, int y, int width, int height,
@Nullable Matrix m, boolean filter) {
checkXYSign(x, y);
checkWidthHeight(width, height);
if (x + width > source.getWidth()) {
throw new IllegalArgumentException("x + width must be <= bitmap.width()");
}
if (y + height > source.getHeight()) {
throw new IllegalArgumentException("y + height must be <= bitmap.height()");
}
// check if we can just return our argument unchanged
if (!source.isMutable() && x == 0 && y == 0 && width == source.getWidth() &&
height == source.getHeight() && (m == null || m.isIdentity())) {
return source;
}
boolean isHardware = source.getConfig() == Config.HARDWARE;
if (isHardware) {
source.noteHardwareBitmapSlowCall();
source = nativeCopyPreserveInternalConfig(source.mNativePtr);
}
int neww = width;
int newh = height;
Bitmap bitmap;
Paint paint;
Rect srcR = new Rect(x, y, x + width, y + height);
RectF dstR = new RectF(0, 0, width, height);
RectF deviceR = new RectF();
//获取图片原有格式
//设置压缩
Config newConfig = Config.ARGB_8888;
final Config config = source.getConfig();
// GIF files generate null configs, assume ARGB_8888
if (config != null) {
switch (config) {
case RGB_565:
newConfig = Config.RGB_565;
break;
case ALPHA_8:
newConfig = Config.ALPHA_8;
break;
case RGBA_F16:
newConfig = Config.RGBA_F16;
break;
//noinspection deprecation
case ARGB_4444:
case ARGB_8888:
default:
newConfig = Config.ARGB_8888;
break;
}
}
if (m == null || m.isIdentity()) {
bitmap = createBitmap(neww, newh, newConfig, source.hasAlpha());
paint = null; // not needed
} else {
final boolean transformed = !m.rectStaysRect();
m.mapRect(deviceR, dstR);
neww = Math.round(deviceR.width());
newh = Math.round(deviceR.height());
Config transformedConfig = newConfig;
if (transformed) {
if (transformedConfig != Config.ARGB_8888 && transformedConfig != Config.RGBA_F16) {
transformedConfig = Config.ARGB_8888;
}
}
bitmap = createBitmap(neww, newh, transformedConfig, transformed || source.hasAlpha());
paint = new Paint();
paint.setFilterBitmap(filter);
if (transformed) {
paint.setAntiAlias(true);
}
}
nativeCopyColorSpace(source.mNativePtr, bitmap.mNativePtr);
// The new bitmap was created from a known bitmap source so assume that
// they use the same density
bitmap.mDensity = source.mDensity;
bitmap.setHasAlpha(source.hasAlpha());
bitmap.setPremultiplied(source.mRequestPremultiplied);
Canvas canvas = new Canvas(bitmap);
canvas.translate(-deviceR.left, -deviceR.top);
canvas.concat(m);
canvas.drawBitmap(source, srcR, dstR, paint);
canvas.setBitmap(null);
if (isHardware) {
return bitmap.copy(Config.HARDWARE, false);
}
return bitmap;
}