Image hue modification in C#

Question

Hi,

I have an image and i want to modify the hue of that particular image to specific value. I know rgb to hsl and hsl to rgb conversion mathematical formula but I am not being able to implement this thing into c#.

Following is the pseudo:

for(x=0;x<image_width;x++)
{
  for(y=0;y<image_height;y++)
  {
    Color oldColor=GetColorFromPixel(x,y);
    Color newColor=ModifyHue(oldColor);
    SetColorPixel(x,y,newColor);    
  }
}

Thanks

Answer 1

If you just want to try out or performance is not critical, the easist way is to use the Bitmap.GetPixel and Bitmap.SetPixel methods:

var bm = new Bitmap(filename);
for(int x=0;x<bm.Width;x++)
{
  for(y=0;y<bm.Height;y++)
  {
    Color oldColor=bm.GetPixel(x,y);
    Color newColor=ModifyHue(oldColor);
    bm.SetPixel(x,y,newColor);    
  }
}

If you want more performant operation, you should look at the Bitmap.LockBits method which fixes the entire bitmap on a memory location and lets you modify this memory directly.

Answer 2

If you want the algorithm in C# look at this. Check if this match with what wiki says...

Answer 3

Due to the fact, that the Color structure already has a GetHue(), GetSaturation() and GetBrightness() it would be nice to also construct a color from these values. So i found the following code somewhere on the net a while ago (currently can't find it again, but it was from a Microsoft guy blog and he also had a test that steps through all KnownColor).

/// <summary>
/// Creates a Color from alpha, hue, saturation and brightness.
/// </summary>
/// <param name="alpha">The alpha channel value.</param>
/// <param name="hue">The hue value.</param>
/// <param name="saturation">The saturation value.</param>
/// <param name="brightness">The brightness value.</param>
/// <returns>A Color with the given values.</returns>
public static Color FromAhsb(int alpha, float hue, float saturation, float brightness)
{

    if (0 > alpha || 255 < alpha)
    {
        throw new ArgumentOutOfRangeException("alpha", alpha,
          "Value must be within a range of 0 - 255.");
    }
    if (0f > hue || 360f < hue)
    {
        throw new ArgumentOutOfRangeException("hue", hue,
          "Value must be within a range of 0 - 360.");
    }
    if (0f > saturation || 1f < saturation)
    {
        throw new ArgumentOutOfRangeException("saturation", saturation,
          "Value must be within a range of 0 - 1.");
    }
    if (0f > brightness || 1f < brightness)
    {
        throw new ArgumentOutOfRangeException("brightness", brightness,
          "Value must be within a range of 0 - 1.");
    }

    if (0 == saturation)
    {
        return Color.FromArgb(alpha, Convert.ToInt32(brightness * 255),
          Convert.ToInt32(brightness * 255), Convert.ToInt32(brightness * 255));
    }

    float fMax, fMid, fMin;
    int iSextant, iMax, iMid, iMin;

    if (0.5 < brightness)
    {
        fMax = brightness - (brightness * saturation) + saturation;
        fMin = brightness + (brightness * saturation) - saturation;
    }
    else
    {
        fMax = brightness + (brightness * saturation);
        fMin = brightness - (brightness * saturation);
    }

    iSextant = (int)Math.Floor(hue / 60f);
    if (300f <= hue)
    {
        hue -= 360f;
    }
    hue /= 60f;
    hue -= 2f * (float)Math.Floor(((iSextant + 1f) % 6f) / 2f);
    if (0 == iSextant % 2)
    {
        fMid = hue * (fMax - fMin) + fMin;
    }
    else
    {
        fMid = fMin - hue * (fMax - fMin);
    }

    iMax = Convert.ToInt32(fMax * 255);
    iMid = Convert.ToInt32(fMid * 255);
    iMin = Convert.ToInt32(fMin * 255);

    switch (iSextant)
    {
        case 1:
            return Color.FromArgb(alpha, iMid, iMax, iMin);
        case 2:
            return Color.FromArgb(alpha, iMin, iMax, iMid);
        case 3:
            return Color.FromArgb(alpha, iMin, iMid, iMax);
        case 4:
            return Color.FromArgb(alpha, iMid, iMin, iMax);
        case 5:
            return Color.FromArgb(alpha, iMax, iMin, iMid);
        default:
            return Color.FromArgb(alpha, iMax, iMid, iMin);
    }
}

With this function you are able to work within the HSB (or HSV) color presentation not within the HSL presentation. For further informations about their differences take a look at this wikipedia article.