Resize bitmap without creating new bitmap

问题

Is there anyway to resize/scale bitmap without creating a new bitmap? Let say i download image that height or width is larger than 2048px. Before i can display it, i have to resize it because ImageView does not support bitmaps larger than 2048px. If i use Bitmap.createScaledBitmap(Bitmap src, int dstWidth, int dstHeight, boolean filter) it gives me a new bitmap. Now we have two bitmaps, original and scaled. Thats when my application runs out of memory.

Below is the code which i use right now.

// Async task to download the image
private ImageView mImage;
private ProgressBar progress;
private Button button;

        @Override
        protected void onPostExecute(Bitmap result){
            progress.setVisibility(View.GONE);
            if(result != null){

                if(result.getHeight() > 2048 || result.getWidth() > 2048){
                    float scaledvalues[] = scale(result.getWidth(), result.getHeight());
                    image = Bitmap.createScaledBitmap(result, (int)scaledvalues[0], (int)scaledvalues[1], false);
                    mImage.setBitmap(image);
                }
                else{
                    image = result;
                    mImage.setBitmap(result);
                }
                button.setEnabled(true);
            }
        }

    //I use this method to calculate new width and height
    public float[] scale(int width, int height){
        float scaledheight = -1f;
        float scaledwidth = -1f;
        float scaledheightpros = -1f;
        float scaledwidthpros = -1f;
        float finalheight = -1f;
        float finalwidth = -1f;
        if(height > 2048){
            scaledheight = height - 2048f;
            float s = scaledheight*100f;
            scaledheightpros = s / 100f;
        }
        if(width > 2048){
            scaledwidth = width - 2048f;
            float z = scaledwidth * 100f;
            scaledwidthpros = z / width;
        }
            if(scaledheightpros > scaledwidthpros){
                float a = height/100f;
                float b = width/100f;
                finalheight = height - (a * scaledheightpros);
                finalwidth = width - (b * scaledheightpros);
            }
            else{
                float a = height/100f;
                float b = width/100f;
                finalheight = height - (a * scaledwidthpros);
                finalwidth = width - (b * scaledwidthpros);
            }

        Log.i(TAG, "startingheight: " + height + " finalheight: " + finalheight + "%: " + scaledheightpros);
        Log.i(TAG, "startingwidth: " + width + " finalwidth: " + finalwidth + "%: " + scaledwidthpros);
        float array[] = {finalwidth, finalheight};
        return array;
    }

回答1:

use sampling if you facing out of memory issue.

public static int calculateInSampleSize(
 BitmapFactory.Options options, int reqWidth, int reqHeight) {
// Raw height and width of image
final int height = options.outHeight;
final int width = options.outWidth;
int inSampleSize = 1;

if (height > reqHeight || width > reqWidth) {

    // Calculate ratios of height and width to requested height and width
    final int heightRatio = Math.round((float) height / (float) reqHeight);
    final int widthRatio = Math.round((float) width / (float) reqWidth);

    // Choose the smallest ratio as inSampleSize value, this will guarantee
    // a final image with both dimensions larger than or equal to the
    // requested height and width.
    inSampleSize = heightRatio < widthRatio ? heightRatio : widthRatio;
}

return inSampleSize;
}

public static Bitmap decodeSampledBitmapFromResource(Resources res, int resId,
    int reqWidth, int reqHeight) {

// First decode with inJustDecodeBounds=true to check dimensions
final BitmapFactory.Options options = new BitmapFactory.Options();
options.inJustDecodeBounds = true;
BitmapFactory.decodeResource(res, resId, options);

// Calculate inSampleSize
options.inSampleSize = calculateInSampleSize(options, reqWidth, reqHeight);

// Decode bitmap with inSampleSize set
options.inJustDecodeBounds = false;
return BitmapFactory.decodeResource(res, resId, options);
}

At the end for setting image in Imageview, use this

 mImageView.setImageBitmap(decodeSampledBitmapFromResource(getResources(),R.id.myimage,    
Screen_width, screen_height));

Must read this

来源：https://stackoverflow.com/questions/16874800/resize-bitmap-without-creating-new-bitmap