tompazourek / colourful Goto Github PK

Hello,
This isn't a question about Colourful; I am trying to understand some code I have inherited that does conversion from CIELab to RGB after decompressing an JPEG 2000 file. I don't know a lot about colour spaces or colour conversions.

If you have a moment, I'm trying to grok the color_cielab_to_rgb method in
this file:

https://github.com/GrokImageCompression/grok/blob/master/src/bin/common/color.cpp

I am trying to understand the code

if(default_type == 0x44454600) { /* DEF : default */
    rl = 100;
    ra = 170;
    rb = 200;
    ol = 0;
    oa = pow(2, prec1 - 1);
    ob = pow(2, prec2 - 2) +  pow(2, prec2 - 3);
} else {
    rl = row[2];
    ra = row[4];
    rb = row[6];
    ol = row[3];
    oa = row[5];
    ob = row[7];
}

Is the code in the else branch a custom CIELab space, and the code above is based on a standard CIELab space ?

If you have time, interested in knowing your take on this.

Thanks,
Aaron

Details: http://en.wikipedia.org/wiki/Colorfulness

CIECAM02 might have some nice features that might be useful for the Colourful library.

Some Java implementation:
https://github.com/igd-geo/pcolor
http://painterly.costar.sfu.ca/

Other links:
http://en.wikipedia.org/wiki/CIECAM02#Chromatic_adaptation
http://www.cis.rit.edu/fairchild/PDFs/AppearanceLec.pdf

Parse according to CSS 3 standard:

http://www.w3.org/TR/css3-color/#colorunits

http://en.wikipedia.org/wiki/LMS_color_space
http://web.stanford.edu/~sujason/ColorBalancing/adaptation.html
http://www.brucelindbloom.com/index.html?Eqn_ChromAdapt.html

Could be done by converter factory maybe.

Maybe I'm doing something wrong, but when I try a basic RGB -> Lab conversion I'm getting a different answer than other converters out there.

var c1 = Color.FromArgb(0, 255, 0);
var c2 = new RGBColor(c1);
var converter = new ColourfulConverter();
var c4 = converter.ToLab(c2);

This gives me Lab [L=87.82, a=-79.29, b=80.99]

But when I try the same conversion on http://colormine.org/convert/rgb-to-lab I get: L = 87.74, a = -86.18, b = 83.18.

Any idea what I'm doing wrong here?

Thanks,
Mike

http://www.venture-ware.com/kevin/coding/lets-learn-math-photoshop-blend-modes/
(archive: http://web.archive.org/web/20131211145340/http://www.venture-ware.com/kevin/coding/lets-learn-math-photoshop-blend-modes/ )

Also interesting seems gamma-adjusted RGB blending.

The color spaces should accept Vector as a constructor, since many blending modes can be universal and applied on color vectors.

See: https://socratic.org/questions/what-is-the-formula-for-the-distance-between-two-polar-coordinates

Implement these factory methods for convenient use:

• FromGrey (1 channel)
• FromRGB8bit

      let rgb = Colourful.RGBColor systemColor 
      let cnvrtr = Colourful.Conversion.ColourfulConverter()
      let lab = cnvrtr.ToLab rgb

same code works fine with v1.2.2

ColorConverter class name directly conflicts with System.Drawing.ColorConverter. It might be better to change its name for easier integration.

Implement ToString()

RGBColor currently enforces values to be 0..1. I would like to work with colors that are outside of the sRGB color gamut but still valid.

Is there a way to do that?

var defaultColor= default(LinearRGBColor);
var converter = new ColourfulConverter();
var actual = converter.Adapt(defaultColor);

Produces an NRE. This also happens with arrays of LinearRGBColor.

• ICC profile parsing
  • https://formats.kaitai.io/icc_4/csharp.html
  • https://www.vintasoft.com/docs/vsimaging-dotnet/Programming-Color_Management.html#IccProfile
  • https://github.com/JBildstein/NCM/tree/master/ColorManager/ICC

Same as RGB, but not using companding on the channels.

Hello,

If you take RGB values (Let's say sRGB) and convert to LAB with D50, do you get exact values like in Photoshop?

Thank You.

I use the latest version 2.0.3 in .NETFramework 4.7.2, when convert XYZColor to RGBColor throw an StackOverflowException exception. The exception message 'System.StackOverflowException was unhandled Message: An unhandled exception of type 'System.StackOverflowException' occurred in Colourful.dll'.

Test code:

                // arange
                var input = new XYZColor(0.96422, 1.00000, 0.82521);
                var converter = new ColourfulConverter { WhitePoint = Illuminants.D50, TargetRGBWorkingSpace = RGBWorkingSpaces.sRGB };

                // act
                var output = converter.ToRGB(input);

Any chance that the code could be down-ported back to .NET 4.6? Unity requires at most .NET 4.6 and this code utilizes .NET 7 functions like "type pattern matching".
The 'in' and 'readonly' keyword can be left out, "get=>" can easily be rewritten and a throw after a double questionmark is easily fixed, but "type pattern matching" needs some rework.

Maybe add unity support in a separate branch? Would you accept a pull request?I could add some extra's to calculate averages from textures etc...

It would be useful to add the Jzazbz color space . Thank you

Replace the dependencies on Math.NET by custom built-in utility classes.

Hello,

I am trying to get the converter working with VB.net but I can't for the life of me figure out what is to go in the new constructor of the ColourfulConverter? Anyone that could help. When I run it like this I get the following error: System.ArgumentOutOfRangeException: 'The maximum value is 1'

Dim input As RGBColor = New RGBColor(Px.R, Px.G, Px.B)
Dim LAB As LabColor
Dim conver = New ColourfulConverter()
LAB = conver.ToLab(input)

Hi there,

Thanks a lot for working on this project. I am trying to process video frames from a Rec2020 ST2084 video file and plot a brightness waveform (Y axis is nits) like I am used to seeing in DaVinci Resolve.

Do you have any end to end example of using your library to access individual frames from a video file?

Thanks!

Nice test data can be obtained from this Java applet:

http://www.brucelindbloom.com/index.html?ColorCheckerCalculator.html

There are values from all supported color spaces, this can properly test the conversion.

For some reason, NuGet contains only DLL and XML docs.

It should contain PDB for better debugging/exception experience.

Maybe we could also consider Source Link?

One of the features that require .NET 4.5 are IReadOnlyList vectors and matrices. These might be substituted with IList or arrays for older .NET versions. Of course, there might also be more problems.

Sorry for this newbie question but;
Is it possible to get the RGB Result in 0-255?
Thanks Lars