How to programmatically change contrast of a bitmap in android?

Question

I want to programmatically change the contrast of bitmap. Till now I have tried this.

private Bitmap adjustedContrast(Bitmap src, double value)
    {
                


        

Answer 1

Here is a Renderscript implementation (from the Gradle Example Projects)

ip.rsh

#pragma version(1)
#pragma rs java_package_name(your.app.package)

contrast.rs

#include "ip.rsh"

static float brightM = 0.f;
static float brightC = 0.f;

void setBright(float v) {
    brightM = pow(2.f, v / 100.f);
    brightC = 127.f - brightM * 127.f;
}

void contrast(const uchar4 *in, uchar4 *out)
{
#if 0
    out->r = rsClamp((int)(brightM * in->r + brightC), 0, 255);
    out->g = rsClamp((int)(brightM * in->g + brightC), 0, 255);
    out->b = rsClamp((int)(brightM * in->b + brightC), 0, 255);
#else
    float3 v = convert_float3(in->rgb) * brightM + brightC;
    out->rgb = convert_uchar3(clamp(v, 0.f, 255.f));
#endif
}

Java

private Bitmap changeBrightness(Bitmap original RenderScript rs) {
    Allocation input = Allocation.createFromBitmap(rs, original);
    final Allocation output = Allocation.createTyped(rs, input.getType());
    ScriptC_contrast mScript = new ScriptC_contrast(rs);
    mScript.invoke_setBright(50.f);
    mScript.forEach_contrast(input, output);
    output.copyTo(original);
    return original;
}

Answer 2

I just had the same problem and ended up using the Color Matrix that Ruslan Yanchyshyn describes. I needed to automatically adjust brightness depending on the image, so I used BoofCV to create a histogram from a scaled version of the image - It took way to long to process the whole image. Then I analyzed the histogram - looked at what was the darkest and brightest colors and then created a color matrix which transforms the colors so the darkest colors are 0 and the brightest colors are 255. In this way the new image uses the whole spectrum from dark/black to light/white now.

Ended up writing a small post on how I did it on our company blog here if anyone are interested. http://appdictive.dk/blog/projects/2016/07/26/levels_with_color_matrix/

Answer 3

http://android.okhelp.cz/bitmap-set-contrast-and-brightness-android/

have a look at this ,this might solve your problem

Answer 4

Assumption - ImageView is used to display the bitmap

I did a more enhancement in the Ruslan's answer

Instead of replacing bitmap every time (which makes it slow if you are using seek bar) we can work on the Color Filter of the ImageView.

float contrast;
float brightness = 0;
ImageView imageView;

// SeekBar ranges from 0 to 90
// contrast ranges from 1 to 10  
mSeekBarContrast.setOnSeekBarChangeListener(new SeekBar.OnSeekBarChangeListener() {
        @Override
        public void onProgressChanged(SeekBar seekBar, int i, boolean b) {
            contrast = (float) (i + 10) / 10;
            // Changing the contrast of the bitmap
            imageView.setColorFilter(getContrastBrightnessFilter(contrast,brightness));
        }

        @Override
        public void onStartTrackingTouch(SeekBar seekBar) {

        }

        @Override
        public void onStopTrackingTouch(SeekBar seekBar) {

        }
});

ColorMatrixColorFilter getContrastBrightnessFilter(float contrast, float brightness) {
    ColorMatrix cm = new ColorMatrix(new float[]
            {
                    contrast, 0, 0, 0, brightness,
                    0, contrast, 0, 0, brightness,
                    0, 0, contrast, 0, brightness,
                    0, 0, 0, 1, 0
            });
    return new ColorMatrixColorFilter(cm);
}

P.S - Brightness can also be changed along with contrast using this method

Answer 5

Try this. Your code didn't work because you create only a mutable bitmap and didn't copy the image of source bitmap to the mutable one if i'm not mistaken.

Hope It helps :)

private Bitmap adjustedContrast(Bitmap src, double value)
{
    // image size
    int width = src.getWidth();
    int height = src.getHeight();
    // create output bitmap

    // create a mutable empty bitmap
    Bitmap bmOut = Bitmap.createBitmap(width, height, src.getConfig());

    // create a canvas so that we can draw the bmOut Bitmap from source bitmap
    Canvas c = new Canvas();
    c.setBitmap(bmOut);

    // draw bitmap to bmOut from src bitmap so we can modify it
    c.drawBitmap(src, 0, 0, new Paint(Color.BLACK));


    // color information
    int A, R, G, B;
    int pixel;
    // get contrast value
    double contrast = Math.pow((100 + value) / 100, 2);

    // scan through all pixels
    for(int x = 0; x < width; ++x) {
        for(int y = 0; y < height; ++y) {
            // get pixel color
            pixel = src.getPixel(x, y);
            A = Color.alpha(pixel);
            // apply filter contrast for every channel R, G, B
            R = Color.red(pixel);
            R = (int)(((((R / 255.0) - 0.5) * contrast) + 0.5) * 255.0);
            if(R < 0) { R = 0; }
            else if(R > 255) { R = 255; }

            G = Color.green(pixel);
            G = (int)(((((G / 255.0) - 0.5) * contrast) + 0.5) * 255.0);
            if(G < 0) { G = 0; }
            else if(G > 255) { G = 255; }

            B = Color.blue(pixel);
            B = (int)(((((B / 255.0) - 0.5) * contrast) + 0.5) * 255.0);
            if(B < 0) { B = 0; }
            else if(B > 255) { B = 255; }

            // set new pixel color to output bitmap
            bmOut.setPixel(x, y, Color.argb(A, R, G, B));
        }
    }
    return bmOut;
}

Answer 6

Maybe you can try this one:

http://xjaphx.wordpress.com/2011/06/21/image-processing-contrast-image-on-the-fly/

Hope that helps! :)