Issue reading colors compared with CAD assistant.

Lorenzo Napl
Thu, 07/13/2023 - 09:54

Forums:

I found some issues when I get colors from a STEP file (I created myself with FreeCad).
The method that I use is searching for all types of colors (gen, curv, surf) and then store them in data like:

Quantity_Color color;
color.SetValues(0.5, 0.5, 0.5, Quantity_TOC_RGB);
XCAFDoc_ColorType colorTypes[] =
{
       XCAFDoc_ColorType::XCAFDoc_ColorGen,
        XCAFDoc_ColorType::XCAFDoc_ColorCurv,
        XCAFDoc_ColorType::XCAFDoc_ColorSurf,
};

for (const XCAFDoc_ColorType& colorType : colorTypes)
{
     if (colorTool->GetColor(label, colorType, color))
    {
       //Save color....

When I compare the results with the ones that I get from saving the same STEP file as OBJ with CAD Asistant:
Colors from custom implementation:

newmtl Material0
     Kd 0.4019778072834015 0 1

newmtl Material1
     Kd 0.06847815960645676 0.06847815960645676 0.16202938556671143

newmtl Material2
     Kd 1 1 0

Colors from CAD Assistant:

newmtl Material_2
     Kd 0.6666667 0 1

newmtl Material_1
     Kd 0.2901961 0.2901961 0.4392157

newmtl Material_3
     Kd 1 1 0

I also attached images for a better comparison.

Best regards, Lorenzo

Attachments:

cadAssistantColors.png

customImplementation.png

Dmitrii Pasukhin
Thu, 07/13/2023 - 11:23

Hello

Problem with color format. The main format for CAD Assistant is sRGB and any colours from step saved as sRGB.

Please take a look into https://dev.opencascade.org/content/occt-3d-viewer-becomes-srgb-aware

Best regards, Dmitrii.

Dmitrii Pasukhin
Thu, 07/13/2023 - 11:26

I find out that XCAF don't care about which format is saved. I think we need to analyse it and improve. Thank you. I will create a issue to keep this idea.

Best regards, Dmitrii.

Lorenzo Napl
Thu, 07/13/2023 - 12:08

Yes seems that changing from Quantity_TOC_RGB to Quantity_TOC_sRGB doesn't fix the issue.
I finally get the good values using Quantity_Color::Convert_LinearRGB_To_sRGB(), so anyone facing a similar issue, this should work.
Thanks again for your work!

Best regards, Lorenzo.

gkv311 n
Thu, 07/13/2023 - 13:39

OBJ relies on a legacy shading model with not well-defined color definition. If you are using some own OBJ writer - make sure to convert color components, as it is done by RWObj_CafWriter:

double anRgb[3] = {};
color.Values(anRgb[0], anRgb[1], anRgb[2], Quantity_TOC_sRGB);

Your code snippets are incomplete, so fill free to share more details if problem is still unclear.

Lorenzo Napl
Thu, 07/13/2023 - 12:11

As stated by Dimitrii, using GetValues with Quantity_TOC_sRGB, return the same values as using it with Quantity_TOC_RGB. The last upper message that I post works as a workaround until they fix it.

Best regards, Lorenzo.

Dmitrii Pasukhin
Thu, 07/13/2023 - 12:21

Quantity_Color::Values(aR,aG,aB, Quantity_TOC_sRGB) calls internally Convert_LinearRGB_To_sRGB. The result should be the same(in latests version of occt)

Best regards, Dmitrii.

Lorenzo Napl
Thu, 07/13/2023 - 13:15

With Quantity_Color::Values(aR,aG,aB, Quantity_TOC_sRGB) seems to work as well.

Thanks!

Best regards, Lorenzo.