How does colorised texture work?

Hi,

I want to know how colorised texture works exactly.
I read that the texture is first converted to gray scale and then the color is applied on top of it.
I tried doing that, multiplying color value with gray scale texture color values. This doesn’t work.

I also read that same hue from color is applied to the gray scale texture. Can anyone explain this?
Do we need to add colors in HSL space?

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A search of the developer categories on this subject:

The answer I like best comes from Andreas:

Hi Dan,
I went through the above link.

But, still it is not clear to me.

This is my understanding:
In case of Colorized Texture, the texture is first converted to gray scale and then the color value is multiplied with the gray scale values.

Is this correct?

I don’t think it’s a tinted grayscale image. It looks bore like saturation and lightness are kept while the hue for each pixel is changed.

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We should probably document this in a page in the documentation. Let start here in making the first attempt - let me know if you need more details.

(EDIT: We now have documented it: https://github.com/SketchUp/sketchup-colorize-algorithm)

SketchUp perform two types of color adjustments:

If you set a material color for a textured material via the Ruby API’s Sketchup::Material.color= it sets the type to Sketchup::Material::COLORIZE_TINT.

You can toggle the type using Sketchup::Material.colorize_type=

The UI have a checkbox:

image

For what is happening on our end:

  • Each pixel is processed one by one.
  • RGB value is converted to HLS.

Sketchup::Material::COLORIZE_SHIFT

  • Adjustment Hue is added to Pixel Hue
  • Hue ensured to be within 0-360 range by rolling around.
  • Adjustment Saturation is added to Pixel Saturation (clamped to 0.0-1.0).
  • Adjustment Lumination is added to Pixel Lumination (clamped to 0.01-1.0).

Sketchup::Material::COLORIZE_TINT

  • Pixel Hue is set to Adjustment Hue
  • Hue ensured to be within 0-360 range by rolling around.
  • Adjustment Saturation is added to Pixel Saturation (clamped to 0.0-1.0).
  • Adjustment Lumination is added to Pixel Lumination (clamped to 0.01-1.0).

Converting back to RGB
If the resulting Pixel Saturation is 0.0 the RGB is set to the Pixel Lumination
If not, regular HLS to RGB conversion

Maybe I should write this out into pseudo code or Ruby code…

Btw, I just noticed that the C API is lacking the properties to determine the deltas and colorization types. That will need to be added.

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And I assume the adjustment hue is the difference between the avarage hue of the original image and the hue of the color the user defined?

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Yes - good catch. The color delta is used to adjust. It’s computed from the texture’s average color and the adjustment color.

Describing how the delta is derived is much easier if I just write it in pseudo-code. (I’ll have to get back on this - maybe tomorrow.) The Ruby API have a method for this already: Sketchup::Material.colorize_deltas http://ruby.sketchup.com/Sketchup/Material.html#colorize_deltas-instance_method

Again the C API is lacking that property.

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Note that using the Ruby API you can export colorized textures since SU2016: Sketchup::Texture#write

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Thank You Thomas.

This is very helpful.

Is there any other way we can know the colorized type (tint or shift) from C API ?

Afraid not - this was a long standing issue with the Ruby API - not being able to know the exact state of the material.
We’re constantly working on fleshing out the C API though - so it will come.

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Hi Thomas,

As you were saying, can you explain the color delta calculation using pseudo code?

Thank You

Sorry - things got really busy. Here’s a quick draft:

def get_deltas(shift = true)
  from = texture.average_color
  to = material.color
  
  # Get HLS of base color.
  base_h, base_s, base_l = from.get_hsl

  # Get HLS of new color.
  h, s, l = to.get_hsl
  
  if to.is_monochrome? && from.is_monochrome?
    h = 0
    s = 0
    l = l - base_l
  else if to.is_monochrome?
    h = 0
    s = -1
    l = l - base_l
  else if from.is_monochrome?
    l = l - base_l
  else
    l = l - base_l
    s = s - base_s
    if shift
      h = h - base_h
    end
  end
    
  return [h, s, l]
end
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Thank you Thomas, this helped a lot.

the pseudo code for calculating deltas and the actual logic of COLORIZE_SHIFT and COLORIZE_TINT you provided gives the full picture of colorized_texture.

Only problem is, Since I am using C SDK, I can’t differentiate between COLORIZE_SHIFT and COLORIZE_TINT.
For now, I assumed it is COLORIZE_TINT by default.

In the GUI shift is the default and you have to actively tick a checkbox to get tint. I can’t say what is the most common though.

This topic was automatically closed 91 days after the last reply. New replies are no longer allowed.

For the record, we have documented the logic in a GitHub repository: https://github.com/SketchUp/sketchup-colorize-algorithm

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