android - 位图压缩 PNG -> JPEG，在 Android 中反之亦然

Question

当我从 PNG 转换为 JPEG，然后将 JPEG 转换为 PNG 时，我遇到了图片大小问题。

            public void onClick(View v) {
            String imageFileName = "/sdcard/Penguins2.png";
            File imageFile = new File(imageFileName);
            if (imageFile.exists()) {
                // Load the image from file
                myBitmap = BitmapFactory.decodeFile(imageFileName);
                // Display the image in the image viewer
                myImageView = (ImageView) findViewById(R.id.my_image_view);
                if (myImageView != null) {
                    myImageView.setImageBitmap(myBitmap);
                }
            }
        }

转换:

    private void processImage() {               
    try {
        String outputPath = "/sdcard/Penguins2.jpg";
        int quality = 100;
        FileOutputStream fileOutStr = new FileOutputStream(outputPath);
        BufferedOutputStream bufOutStr = new BufferedOutputStream(
                fileOutStr);
        myBitmap.compress(CompressFormat.JPEG, quality, bufOutStr);
        bufOutStr.flush();
        bufOutStr.close();
    } catch (FileNotFoundException exception) {
        Log.e("debug_log", exception.toString());
    } catch (IOException exception) {
        Log.e("debug_log", exception.toString());
    }
    myImageView.setImageBitmap(myBitmap);

处理完这个操作后，我只需更改这些行:

String imageFileName = "/sdcard/Penguins2.png";

到

String imageFileName = "/sdcard/Penguins2.jpg";

和

String outputPath = "/sdcard/Penguins2.jpg";
(...)
myBitmap.compress(CompressFormat.JPEG, quality, bufOutStr);    

到

String outputPath = "/sdcard/Penguins2.png";
(...)
myBitmap.compress(CompressFormat.PNG, quality, bufOutStr);    

图像大小从 585847 更改为 531409(在 DDMS 中)

我想做这样的事情，因为我想使用 PNG，它对某些图像处理是无损的。然后将图像转换为 jpeg 并作为 MMS 发送，我不确定，但我认为 JPEG 是 MMS 中所有设备都支持的唯一格式。接收器将打开图像并将其转换回 png 而不会丢失数据。

Answer 1

除了@Sherif elKhatib 的回答，如果您查看文档:http://developer.android.com/reference/android/graphics/Bitmap.html#compress%28android.graphics.Bitmap.CompressFormat,%20int,%20java.io.OutputStream%29

您可以看到 PNG 图像没有使用质量参数:

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