Scaling bitmap to 80 percent

Question

I am trying to scale a bitmap using options.inSampleSize, but by what I understand the mapping goes like this

If inSampleSize 1 then the resulting image is 100%
If inSampleSize 2 then the resulting image is 50%
If inSampleSize 3 then the resulting image is 33%
If inSampleSize 4 then the resulting image is 25%
If inSampleSize 5 then the resulting image is 20%

But what I want is a resulting image that is 80% to scale. How do I get that?

score 18 · Answer 1 · edited May 06 '13 at 04:16

18

Could you not use the Bitmap.createScaledBitmap method?

int srcWidth = srcBitmap.getWidth();
int srcHeight = srcBitmap.getHeight();
int dstWidth = (int)(srcWidth*0.8f);
int dstHeight = (int)(srcHeight*0.8f);
Bitmap dstBitmap = Bitmap.createScaledBitmap(srcBitmap, dstWidth, dstHeight, true);

edited May 06 '13 at 04:16

yoah

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answered May 06 '13 at 04:04

James Holderness

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Best answer over here :) – CandleCoder Mar 04 '16 at 09:34
Note that this does not respect the aspect ratio of the original bitmap – Nima Mar 31 '17 at 18:22

score 2 · Answer 2 · 2013-10-11T13:43:27.047

You can use calculateSampleSize function from this class. It is purely calculation based.

package com.abhan.example.util;

import android.content.res.Resources;
import android.graphics.Bitmap;
import android.graphics.Bitmap.Config;
import android.graphics.BitmapFactory;
import android.graphics.BitmapFactory.Options;
import android.graphics.Canvas;
import android.graphics.Paint;
import android.graphics.Rect;

public class ScalingUtilities {

    public static Bitmap decodeResource(Resources res, int resId, int dstWidth,
            int dstHeight, ScalingLogic scalingLogic) {
        Options options = new Options();
        options.inJustDecodeBounds = true;
        BitmapFactory.decodeResource(res, resId, options);
        options.inJustDecodeBounds = false;
        options.inSampleSize = calculateSampleSize(options.outWidth,
                options.outHeight, dstWidth, dstHeight, scalingLogic);
        Bitmap unscaledBitmap = BitmapFactory.decodeResource(res, resId,
                options);

        return unscaledBitmap;
    }

    public static Bitmap createScaledBitmap(Bitmap unscaledBitmap,
            int dstWidth, int dstHeight, ScalingLogic scalingLogic) {
        Rect srcRect = calculateSrcRect(unscaledBitmap.getWidth(),
                unscaledBitmap.getHeight(), dstWidth, dstHeight, scalingLogic);
        Rect dstRect = calculateDstRect(unscaledBitmap.getWidth(),
                unscaledBitmap.getHeight(), dstWidth, dstHeight, scalingLogic);
        Bitmap scaledBitmap = Bitmap.createBitmap(dstRect.width(),
                dstRect.height(), Config.ARGB_8888);
        Canvas canvas = new Canvas(scaledBitmap);
        canvas.drawBitmap(unscaledBitmap, srcRect, dstRect, new Paint(
                Paint.FILTER_BITMAP_FLAG));

        return scaledBitmap;
    }

    public static enum ScalingLogic {
        CROP, FIT
    }

    public static int calculateSampleSize(int srcWidth, int srcHeight,
            int dstWidth, int dstHeight, ScalingLogic scalingLogic) {
        if (scalingLogic == ScalingLogic.FIT) {
            final float srcAspect = (float) srcWidth / (float) srcHeight;
            final float dstAspect = (float) dstWidth / (float) dstHeight;

            if (srcAspect > dstAspect) {
                return srcWidth / dstWidth;
            } else {
                return srcHeight / dstHeight;
            }
        } else {
            final float srcAspect = (float) srcWidth / (float) srcHeight;
            final float dstAspect = (float) dstWidth / (float) dstHeight;

            if (srcAspect > dstAspect) {
                return srcHeight / dstHeight;
            } else {
                return srcWidth / dstWidth;
            }
        }
    }

    public static Rect calculateSrcRect(int srcWidth, int srcHeight,
            int dstWidth, int dstHeight, ScalingLogic scalingLogic) {
        if (scalingLogic == ScalingLogic.CROP) {
            final float srcAspect = (float) srcWidth / (float) srcHeight;
            final float dstAspect = (float) dstWidth / (float) dstHeight;

            if (srcAspect > dstAspect) {
                final int srcRectWidth = (int) (srcHeight * dstAspect);
                final int srcRectLeft = (srcWidth - srcRectWidth) / 2;
                return new Rect(srcRectLeft, 0, srcRectLeft + srcRectWidth,
                        srcHeight);
            } else {
                final int srcRectHeight = (int) (srcWidth / dstAspect);
                final int scrRectTop = (int) (srcHeight - srcRectHeight) / 2;
                return new Rect(0, scrRectTop, srcWidth, scrRectTop
                        + srcRectHeight);
            }
        } else {
            return new Rect(0, 0, srcWidth, srcHeight);
        }
    }

    public static Rect calculateDstRect(int srcWidth, int srcHeight,
            int dstWidth, int dstHeight, ScalingLogic scalingLogic) {
        if (scalingLogic == ScalingLogic.FIT) {
            final float srcAspect = (float) srcWidth / (float) srcHeight;
            final float dstAspect = (float) dstWidth / (float) dstHeight;

            if (srcAspect > dstAspect) {
                return new Rect(0, 0, dstWidth, (int) (dstWidth / srcAspect));
            } else {
                return new Rect(0, 0, (int) (dstHeight * srcAspect), dstHeight);
            }
        } else {
            return new Rect(0, 0, dstWidth, dstHeight);
        }
    }

}

I hope this can help you out.

Thanks.

score -1 · Accepted Answer · answered May 06 '13 at 03:39

-1

I think you may be misunderstanding the point of inSampleSize. It's designed to save memory. If you're just trying to draw the image at 80% its size then you can use a matrix to resize it down (or up) after you've read the file into memory.

answered May 06 '13 at 03:39

csamsonrun

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Will the resize be to scale? – Pouton Gerald May 06 '13 at 03:40
if you scale the image using a matrix it will be to scale if you use the same float for both params in the scale call. Here's an example... http://stackoverflow.com/questions/8722359/scale-rotate-bitmap-using-matrix-in-android – csamsonrun May 06 '13 at 03:41
Thanks for sharing your knowledge with me, and +1 too. – Pouton Gerald May 06 '13 at 04:42

Scaling bitmap to 80 percent

3 Answers3