Solution to the problem that the local background saved in android bitmap is black and nothing can be seen clearly

Preface

Recently, there is an electronic signature function in the project, which requires the customer's handwritten signature and then saves it locally and uploads it to the cloud.

 //获取bitmap
  Bitmap bitmapFromView = mSignatureView.getBitmapFromView();
  BitmapUtil.saveImageToGallery(this, bitmapFromView);

压缩为JPEG格式
I have modified the saveImageToGallery method that was used beforeBitmap.CompressFormat.JPEG

压缩为WEBP无损格式
The core modification content is to modify the format of the compressed image of bitmapBitmap.CompressFormat.WEBP_LOSSLESS

View the source code and you can see the CompressFormat enumeration class

 public enum CompressFormat {
    
    
        /**
         * 压缩为JPEG格式
         * 压缩到最小尺寸
         */
        JPEG          (0),
        /**
         *压缩为PNG格式。
         */
        PNG           (1),
      
        /**
         *压缩为WEBP格式。
         */
        WEBP          (2),
        /**
         *压缩为WEBP有损格式
         */
        WEBP_LOSSY    (3),
        /**
         *压缩为WEBP无损格式。
         */
        WEBP_LOSSLESS (4);

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

save local

To save the bitmap locally, you need to generate a new directory. If there is no directory, create a new folder
Then change the bitmap image generation format to
bmp.compress(Bitmap.CompressFormat.WEBP_LOSSLESS, 100, fos);
Finally refresh the album< /span>
MediaScannerConnection.scanFile

 /**
     * 保存图片到相册
     *
     * @param context 应用程序上下文
     * @param bmp     需要保存的 bitmap
     */
    public static void saveImageToGallery(Context context, Bitmap bmp) {
    
    
        File appDir = new File(Environment.getExternalStorageDirectory(), "Pictures");
        if (!appDir.exists()) {
    
    
            appDir.mkdirs();
        }
        String fileName = "photo_" + System.currentTimeMillis() + ".png";
        File file = new File(appDir, fileName);
        try {
    
    
            FileOutputStream fos = new FileOutputStream(file);
            bmp.compress(Bitmap.CompressFormat.WEBP_LOSSLESS, 100, fos);
            fos.flush();
            fos.close();
        } catch (Exception e) {
    
    
            e.printStackTrace();
        }
        MediaScannerConnection.scanFile(context, 
        new String[]{
    
    file.toString()}, null, null);
    }

Solve the background black

Use canvas to change the background color of the bitmap generated by taking a photo or handwritten electronic signature.

Bitmap newBitmap = Bitmap.createBitmap(bitmap.getWidth(), bitmap.getHeight(), Bitmap.Config.ARGB_8888);
Canvas canvas = new Canvas(newBitmap);
canvas.drawColor(Color.WHITE);
canvas.drawBitmap(bitmap, 0, 0, null);