Applying contrast makes the image black

Question

Here's my contrast script:

 public void ApplyContrast(string contrast)
     {
             double contrastD = Convert.ToDouble(contrast);
             
             Texture2D bitmapImage = new Texture2D(imgTexture.width, imgTexture.height);
 
             if (contrastD < -100) contrastD = -100;
             if (contrastD > 100) contrastD = 100;
             contrastD = (100.0 + contrastD) / 100.0;
             contrastD *= contrastD;
             Color color;
             for (int i = 0; i < bitmapImage.width; i++)
             {
                 for (int j = 0; j < bitmapImage.height; j++)
                 {
                     color = (imgTexture as Texture2D).GetPixel(i, j);
 
                     //Alpha 
                     double pA = color.a / 255.0;
 
                     //Red 
                     double pR = color.r / 255.0;
                     pR -= 0.5;
                     pR *= contrastD;
                     pR += 0.5;
                     pR *= 255;
                     if (pR < 0) pR = 0;
                     if (pR > 255) pR = 255;
 
                     //Green
                     double pG = color.g / 255.0;
                     pG -= 0.5;
                     pG *= contrastD;
                     pG += 0.5;
                     pG *= 255;
                     if (pG < 0) pG = 0;
                     if (pG > 255) pG = 255;
 
                     //Blue
                     double pB = color.b / 255.0;
                     pB -= 0.5;
                     pB *= contrastD;
                     pB += 0.5;
                     pB *= 255;
                     if (pB < 0) pB = 0;
                     if (pB > 255) pB = 255;
 
                     bitmapImage.SetPixel(i, j, new Color((float)pR,(float)pG,(float)pB,(float)pA));
                 }
             }
 
             bitmapImage.Apply();
 
             Image.renderer.material.mainTexture = bitmapImage as Texture;
     }

I noticed if there is no contrast on the image, the image is loaded correctly but as soon as I apply some contrast starting from 1 to some value, the image turns black. What's wrong with the contrast script above?

Answer 1

Best Answer

Answer by revolute · Mar 12, 2015 at 03:49 PM

RGB values in Color is between 0 and 1. Your code

 double pR = color.r / 255.0;
                      pR -= 0.5;
                      pR *= contrastD;
                      pR += 0.5;
                      pR *= 255;

makes it go below 0.

If color.r value is at its highest, color.r == 1. Even at with this value, 1/255 - 0.5 will yield negative values that following code cannot set back to positive values.

Just dont divide by 255 and you will have a not-black texture.

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revolute · Mar 12, 2015 at 03:50 PM 0

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And dont multiply it by 255 at the end or it will be all white.

Eowyn27 · Mar 12, 2015 at 03:57 PM 0

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Okay, I'll give it a try. Also I want to double check and say, that I would like to restrict changing my contrast values from 0% to 100%. No negative values or above 100. Thanks.

EDIT: So it works similarly to how I had it before but the contrast algo, this one, isn't very good. I wonder why it doesn't look like some of the more professional algos for contrast.

Eowyn27 · Mar 14, 2015 at 01:34 AM 0

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@revolute, the same thing is happening in my brightness script! http://answers.unity3d.com/questions/923493/brightness-script-makes-image-completely-black-and.html

Eowyn27 · Mar 14, 2015 at 06:23 PM 0

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@revolute, I've been comparing the brightness and contrast script and it seems like the scaling for both are off. The brightness script looks fine but the contrast script looks very "cartoony". I changed my contrast script to include a corrector factor: double mappedContrast = (2*contrastD) - 100; where the script above is for contrast of -100 to 100 and the string that gets passed is from 0 to 100.

revolute · Mar 15, 2015 at 03:26 PM 0

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Sorry but I dont think I can help you there. I can help you make the code work but not make the code get results you wish to get.

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Applying contrast makes the image black

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