What exactly does img.RGBtoXYZ() do ?

[pwplus7]

If img has pixel data ordered with RGB format i.e. R1,G1,B1, R2,G2,B2, ... ?? Is img.RGBtoXYZ() supposed to change the data ordering to CImg format i.e. R1,R2,R3... G1,G2,G3... B1,B2,B3...

[dtschump]

img.RGBtoXYZ() assumes your instance is an image with 3 channels, each channel representing the R,G,B components of the image. With CImg, the corresponding buffer is stored in non-interleaved format, so : R1 R2 R3... G1 G2 G3... B1 B2 B3.... This method converts each RGB value of such an image into a XYZ representation (see https://en.wikipedia.org/wiki/CIE_1931_color_space).

[pwplus7]

Thank You David.. I was completely off-base, until I received you note, I misunderstood CImg::RGB2XYZ() to be a conversion from inter-leaved RGB to non-interleaved CImg image format; and, thus could not understand why it was wiping out my CImg<T> pixel data.

I love working with CImg and I'm trying to learn as much as possible about it by reading the PDF reference document, which I find very brief in some sections.

Many Thanks for making CImg available to the public, it is truly one of the best C++ packages I've ever encountered.

L Godio, from Atlanta, GA USA

On Tue, Sep 1, 2020 at 4:02 PM David Tschumperlé [email protected] wrote:

img.RGBtoXYZ() assumes your instance is an image with 3 channels, each channel representing the R,G,B components of the image. With CImg, the corresponding buffer is stored in non-interleaved format, so : R1 R2 R3... G1 G2 G3... B1 B2 B3.... This method converts each RGB value of such an image into a XYZ representation (see https://en.wikipedia.org/wiki/CIE_1931_color_space).

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[dtschump]

Thanks for the kind words. If you need a function to deinterlace a color buffer from RGBRGBRGB... to RRRRR...GGGG...BBBB (and vice-versa), then you may have a look to CImg<T>::permute_axes().

[pwplus7]

OK, ? If I want to convert from inter-leaved RGB to non-interleaved CImg image format , what 'axis_order' do I pass to permute_axes ( const char ∗const axes_order ) ?

[dtschump]

Assuming you have, e.g. a unsigned char *buffer encoding a RGB image with size WxH, then

CImg<unsigned char> img = CImg<unsigned char>(buffer,3,W,H).permute_axes("yzcx");

should do the job.