图片质量压缩 与 图片格式 JPEG PNG

Bitmap.compress()图片质量压缩方法

提到：

<>PNG是一种无损lossess压缩方式，compress方法中quality字段的设置是无效的，JPEG是不透明opaque压缩。

<>像素深度 bitdepth 的概念

/**
* Write a compressed version of the bitmap to the specified outputstream.
* If this returns true, the bitmap can be reconstructed by passing a
* corresponding inputstream to BitmapFactory.decodeStream(). Note: not
* all Formats support all bitmap configs directly, so it is possible that
* the returned bitmap from BitmapFactory could be in a different bitdepth,
* and/or may have lost per-pixel alpha (e.g. JPEG only supports opaque
* pixels).
*
* @param format   The format of the compressed image
* @param quality  Hint to the compressor, 0-100. 0 meaning compress for
*                 small size, 100 meaning compress for max quality. Some
*                 formats, like PNG which is lossless, will ignore the
*                 quality setting
* @param stream   The outputstream to write the compressed data.
* @return true if successfully compressed to the specified stream.
*/
public boolean Bitmap.compress(CompressFormat format, int quality, OutputStream stream);

图片压缩格式 枚举类型Bitmap.CompressFormat

/**
* Specifies the known formats a bitmap can be compressed into
*/
public enum CompressFormat {
JPEG (0),
PNG (1),
WEBP (2);

CompressFormat(int nativeInt) {
this.nativeInt = nativeInt;
}
final int nativeInt;
}