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POAndroid Histogram equalization algorithm gives me really bright or red image
 

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  1. POAndroid Histogram equalization algorithm gives me really bright or red image
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    <p>I am doing histogram equalization on an image. I first get the RGB image and convert it to YUV. I run the histogram equalization algorithm on Y' of YUV and then convert back to RGB. Is it me, or does the image look weird? I am doing this correctly? this image is pretty bright, other images are a little red.</p> <p>Here are the before/after images:</p> <p><img src="https://adblogcat.com/wp-content/uploads/2012/07/1335218187675-150x150.jpg" alt="before"> <img src="https://adblogcat.com/wp-content/uploads/2012/07/9KB1MOGC9P-150x150.jpg" alt="after"></p> <p>The algorithm (the commented values are values that I used previously for conversion. Both yield pretty much the same results) :</p> <pre><code> public static void createContrast(Bitmap src) { int width = src.getWidth(); int height = src.getHeight(); Bitmap processedImage = Bitmap.createBitmap(width, height, src.getConfig()); int A = 0,R,G,B; int pixel; float[][] Y = new float[width][height]; float[][] U = new float[width][height]; float[][] V = new float [width][height]; int [] histogram = new int[256]; Arrays.fill(histogram, 0); int [] cdf = new int[256]; Arrays.fill(cdf, 0); float min = 257; float max = 0; for(int x = 0; x &lt; width; ++x) { for(int y = 0; y &lt; height; ++y) { pixel = src.getPixel(x, y); //Log.i("TEST","("+x+","+y+")"); A = Color.alpha(pixel); R = Color.red(pixel); G = Color.green(pixel); B = Color.blue(pixel); /*Log.i("TESTEST","R: "+R); Log.i("TESTEST","G: "+G); Log.i("TESTEST","B: "+B);*/ // convert to YUV /*Y[x][y] = 0.299f * R + 0.587f * G + 0.114f * B; U[x][y] = 0.492f * (B-Y[x][y]); V[x][y] = 0.877f * (R-Y[x][y]);*/ Y[x][y] = 0.299f * R + 0.587f * G + 0.114f * B; U[x][y] = 0.565f * (B-Y[x][y]); V[x][y] = 0.713f * (R-Y[x][y]); // create a histogram histogram[(int) Y[x][y]]+=1; // get min and max values if (Y[x][y] &lt; min){ min = Y[x][y]; } if (Y[x][y] &gt; max){ max = Y[x][y]; } } } cdf[0] = histogram[0]; for (int i=1;i&lt;=255;i++){ cdf[i] = cdf[i-1] + histogram[i]; //Log.i("TESTEST","cdf of: "+i+" = "+cdf[i]); } float minCDF = cdf[(int)min]; float denominator = width*height - minCDF; //Log.i("TEST","Histeq Histeq Histeq Histeq Histeq Histeq"); for(int x = 0; x &lt; width; ++x) { for(int y = 0; y &lt; height; ++y) { //Log.i("TEST","("+x+","+y+")"); pixel = src.getPixel(x, y); A = Color.alpha(pixel); Y[x][y] = ((cdf[ (int) Y[x][y]] - minCDF)/(denominator)) * 255; /*R = minMaxCalc(Y[x][y] + 1.140f * V[x][y]); G = minMaxCalc (Y[x][y] - 0.395f * U[x][y] - 0.581f * V[x][y]); B = minMaxCalc (Y[x][y] + 2.032f * U[x][y]);*/ R = minMaxCalc(Y[x][y] + 1.140f * V[x][y]); G = minMaxCalc (Y[x][y] - 0.344f * U[x][y] - 0.714f * V[x][y]); B = minMaxCalc (Y[x][y] + 1.77f * U[x][y]); //Log.i("TESTEST","A: "+A); /*Log.i("TESTEST","R: "+R); Log.i("TESTEST","G: "+G); Log.i("TESTEST","B: "+B);*/ processedImage.setPixel(x, y, Color.argb(A, R, G, B)); } } </code></pre> <p>}</p> <p>My next step is to graph the histograms before and after. I just want to get an opinion here.</p>
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    1. PTQuestion
    1. USCommunity
    1. USJuan Acevedo
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    1. VO
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      1. POAndroid Histogram equalization algorithm gives me really bright or red image
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      1. VTUpMod
    2. VO
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      1. POAndroid Histogram equalization algorithm gives me really bright or red image
      1. USfalro
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    3. VO
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      1. VTUpMod
    1. COI'd start by creating test images with several blocks of solid color to test this.
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      1. POAndroid Histogram equalization algorithm gives me really bright or red image
      1. USRafael Baptista
    2. COThat image looks pretty good to me. I expect your algorithm to brighten an image to the point where some part of it is pure white. If you're getting some redness, that's bad. Make sure your RGB->YUV->RGB path (without equalization) really is the identity function.
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      1. POAndroid Histogram equalization algorithm gives me really bright or red image
      1. USKeith Randall
    3. COThank you both for the comments. First I will use a solid color to see the results and secondly on a solid color image I will make sure I am getting the same image back when running the convertion without histeq.
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      1. POAndroid Histogram equalization algorithm gives me really bright or red image
      1. USJuan Acevedo
 

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