robert hue - Developer IT

Hue, saturation, brightness, contrast effect in hlsl

- by Vibhore Tanwer

I am new to pixel shader, and I am trying to write a simple brightness, contrast, hue, saturation effect. I have written a shader for it but I doubt that my shader is not providing me correct result, Brightness, contrast, saturation is working fine, problem is with hue. if I apply hue between -1 to 1, it seems to be working fine, but to make things more sharp, I need to apply hue value between -180 and 180, like we can apply hue in Paint.NET. Here is my code. // Amount to shift the Hue, range 0 to 6 float Hue; float Brightness; float Contrast; float Saturation; float Alpha; sampler Samp : register(S0); // Converts the rgb value to hsv, where H's range is -1 to 5 float3 rgb_to_hsv(float3 RGB) { float r = RGB.x; float g = RGB.y; float b = RGB.z; float minChannel = min(r, min(g, b)); float maxChannel = max(r, max(g, b)); float h = 0; float s = 0; float v = maxChannel; float delta = maxChannel - minChannel; if (delta != 0) { s = delta / v; if (r == v) h = (g - b) / delta; else if (g == v) h = 2 + (b - r) / delta; else if (b == v) h = 4 + (r - g) / delta; } return float3(h, s, v); } float3 hsv_to_rgb(float3 HSV) { float3 RGB = HSV.z; float h = HSV.x; float s = HSV.y; float v = HSV.z; float i = floor(h); float f = h - i; float p = (1.0 - s); float q = (1.0 - s * f); float t = (1.0 - s * (1 - f)); if (i == 0) { RGB = float3(1, t, p); } else if (i == 1) { RGB = float3(q, 1, p); } else if (i == 2) { RGB = float3(p, 1, t); } else if (i == 3) { RGB = float3(p, q, 1); } else if (i == 4) { RGB = float3(t, p, 1); } else /* i == -1 */ { RGB = float3(1, p, q); } RGB *= v; return RGB; } float4 mainPS(float2 uv : TEXCOORD) : COLOR { float4 col = tex2D(Samp, uv); float3 hsv = rgb_to_hsv(col.xyz); hsv.x += Hue; // Put the hue back to the -1 to 5 range //if (hsv.x > 5) { hsv.x -= 6.0; } hsv = hsv_to_rgb(hsv); float4 newColor = float4(hsv,col.w); float4 colorWithBrightnessAndContrast = newColor; colorWithBrightnessAndContrast.rgb /= colorWithBrightnessAndContrast.a; colorWithBrightnessAndContrast.rgb = colorWithBrightnessAndContrast.rgb + Brightness; colorWithBrightnessAndContrast.rgb = ((colorWithBrightnessAndContrast.rgb - 0.5f) * max(Contrast + 1.0, 0)) + 0.5f; colorWithBrightnessAndContrast.rgb *= colorWithBrightnessAndContrast.a; float greyscale = dot(colorWithBrightnessAndContrast.rgb, float3(0.3, 0.59, 0.11)); colorWithBrightnessAndContrast.rgb = lerp(greyscale, colorWithBrightnessAndContrast.rgb, col.a * (Saturation + 1.0)); return colorWithBrightnessAndContrast; } technique TransformTexture { pass p0 { PixelShader = compile ps_2_0 mainPS(); } } Please If anyone can help me learning what am I doing wrong or any suggestions? Any help will be of great value. EDIT: Images of the effect at hue 180: On the left hand side, the effect I got with @teodron answer. On the right hand side, The effect Paint.NET gives and I'm trying to reproduce.

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