Given an RGB value, how do I create a tint (or shade)?

Question

Among several options for shading and tinting:

• For shades, multiply each component by 1/4, 1/2, 3/4, etc., of its previous value. The smaller the factor, the darker the shade.

• For tints, calculate (255 - previous value), multiply that by 1/4, 1/2, 3/4, etc. (the greater the factor, the lighter the tint), and add that to the previous value (assuming each.component is a 8-bit integer).

Note that color manipulations (such as tints and other shading) should be done in linear RGB. However, RGB colors specified in documents or encoded in images and video are not likely to be in linear RGB, in which case a so-called inverse transfer function needs to be applied to each of the RGB color's components. This function varies with the RGB color space. For example, in the sRGB color space (which can be assumed if the RGB color space is unknown), this function is roughly equivalent to raising each sRGB color component (ranging from 0 through 1) to a power of 2.2. (Note that "linear RGB" is not an RGB color space.)

See also Violet Giraffe's comment about "gamma correction".

Some definitions

• A shade is produced by "darkening" a hue or "adding black"
• A tint is produced by "ligthening" a hue or "adding white"

Creating a tint or a shade

Depending on your Color Model, there are different methods to create a darker (shaded) or lighter (tinted) color:

• RGB:

  • To shade:

    newR = currentR * (1 - shade_factor)
    newG = currentG * (1 - shade_factor)
    newB = currentB * (1 - shade_factor)
    

  • To tint:

    newR = currentR + (255 - currentR) * tint_factor
    newG = currentG + (255 - currentG) * tint_factor
    newB = currentB + (255 - currentB) * tint_factor
    

  • More generally, the color resulting in layering a color RGB(currentR,currentG,currentB) with a color RGBA(aR,aG,aB,alpha) is:

    newR = currentR + (aR - currentR) * alpha
    newG = currentG + (aG - currentG) * alpha
    newB = currentB + (aB - currentB) * alpha
    

  where (aR,aG,aB) = black = (0,0,0) for shading, and (aR,aG,aB) = white = (255,255,255) for tinting

• HSV or HSB:

  • To shade: lower the Value / Brightness or increase the Saturation
  • To tint: lower the Saturation or increase the Value / Brightness
• HSL:
  • To shade: lower the Lightness
  • To tint: increase the Lightness

There exists formulas to convert from one color model to another. As per your initial question, if you are in RGB and want to use the HSV model to shade for example, you can just convert to HSV, do the shading and convert back to RGB. Formula to convert are not trivial but can be found on the internet. Depending on your language, it might also be available as a core function :

• RGB to HSV color in javascript?
• Convert RGB value to HSV

Comparing the models

• RGB has the advantage of being really simple to implement, but:
  • you can only shade or tint your color relatively
  • you have no idea if your color is already tinted or shaded
• HSV or HSB is kind of complex because you need to play with two parameters to get what you want (Saturation & Value / Brightness)
• HSL is the best from my point of view:
  • supported by CSS3 (for webapp)
  • simple and accurate:
    • 50% means an unaltered Hue
    • >50% means the Hue is lighter (tint)
    • <50% means the Hue is darker (shade)
  • given a color you can determine if it is already tinted or shaded
  • you can tint or shade a color relatively or absolutely (by just replacing the Lightness part)

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• If you want to learn more about this subject: Wiki: Colors Model
• For more information on what those models are: Wikipedia: HSL and HSV

I'm currently experimenting with canvas and pixels... I'm finding this logic works out for me better.

1. Use this to calculate the grey-ness ( luma ? )
2. but with both the existing value and the new 'tint' value
3. calculate the difference ( I found I did not need to multiply )

4. add to offset the 'tint' value

   var grey =  (r + g + b) / 3;    
   var grey2 = (new_r + new_g + new_b) / 3;
   
   var dr =  grey - grey2 * 1;    
   var dg =  grey - grey2 * 1    
   var db =  grey - grey2 * 1;  
   
   tint_r = new_r + dr;    
   tint_g = new_g + dg;   
   tint_b = new_b _ db;
   

or something like that...