title: Change the intensity of an image by comparing intensity of another image - OpenTK
body: <p>I have two images. I have to found the points of first image which have intensity greater than 0.8. At the same time I have to found the intensity of second image on same points and need to adjust the light on second image on same points with a threshold/slider value(ranges from 0 to 1). I have done like below. Getting black or dark area on points have intensity greater than 0.8. 
  I'm trying with z value of HSV.<br>
  But instead of this black area I should be able to adjust the light on image2. How can  I achieve this? </p>
  
  <pre><code>public void CreateShaders()
  {
      /***********Vert Shader********************/
      vertShader = GL.CreateShader(ShaderType.VertexShader);
      GL.ShaderSource(vertShader, @"
          attribute vec3 a_position;
          varying vec2 vTexCoordIn; 
          void main() {
              vTexCoordIn=( a_position.xy+1)/2 ;
              gl_Position = vec4(a_position,1);
          }");
      GL.CompileShader(vertShader);
  
      /***********Frag Shader ****************/
      fragShader = GL.CreateShader(ShaderType.FragmentShader);
      GL.ShaderSource(fragShader, @"
          precision highp float;
  
          uniform sampler2D sTexture1;
          uniform sampler2D sTexture2;  
          varying vec2 vTexCoordIn;
          const float Epsilon = 1e-10;
          uniform float sSelectedIntensity1;//slider value 0 to 1
          void main ()
          {
              vec2 vTexCoord=vec2(vTexCoordIn.x,vTexCoordIn.y);    
              vec4  color1 = texture2D (sTexture1, vTexCoord);
              vec4  color2= texture2D (sTexture2, vTexCoord);
              vec3  col1_hsv = RGBtoHSV(color1.rgb);
              float col1_intensity =col1_hsv.z;
              float ConstVal=0.8;
  
              if(col1_intensity&gt;ConstVal)
              { 
                  vec3 col_hsv = RGBtoHSV(color2.rgb);
                  col_hsv.z *= sSelectedIntensity1;//slider value 0 to 1 
                  vec3 col_rgb = HSVtoRGB(col_hsv.rgb);
                  gl_FragColor = vec4(col_rgb.rgb, color2.a);
              }
              else
              {  
                  gl_FragColor = color2;
              }
          }");
      GL.CompileShader(fragShader);
  }
  </code></pre>
  
  <p><a href="https://i.stack.imgur.com/ewh0D.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/ewh0D.png" alt="iNput "></a></p>
  
  <p><a href="https://i.stack.imgur.com/Pau4y.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/Pau4y.png" alt="OUTpUT"></a></p>
  
  <p>Practically, if image1 and image2 are frames coming from two adjusent cameras cam1 and cam2 respectively. And if I put a flash  light  infront of cam1, i should be able to dim/remove this light effect on frames of camera 2.</p>