How to generate RGB by 7 channel coded from CMYK mode

[YubinXie]

There are actually 7 colors that can be generated in CMYK mode, cyan, magenta, yellow, black, red, green, and blue. If I have a 7 channel array (tiff), how can I generated an image with these 7 colors in RGB mode? Many thanks.

[homm]

It's not clear to me, what do you mean and try to achieve.

There are actually 7 colors that can be generated in CMYK mode

Each mode (both CMYK and RGB) can hold millions of colors. CMYK mode consists of four color channels: cyan, magenta, yellow, black. While RGB consists of red, green, and blue.

If I have a 7 channel array (tiff)

Images with all 7 channels don't make sense because information in CMYK channels will contradict with information in RGB channels.

[YubinXie]

Thanks for the reply. I have a 7-channel tiff image and I want to display it with 1 color for each channel (cyan, magenta, yellow, black, red, green, and blue). The final image would be a RGB image.

[homm]

Correct me if I'm wrong, but TIFFs can't hold CMYK and RGB information simultaneously. According to specification, PhotometricInterpretation tag can be only one in the file and there is no value which allows holding both CMYK and RGB in one image.

[homm]

Maybe you can provide a small example?

[YubinXie]

Speaking of format, I believe you are right. I just wonder if there is way to display a 7-slice image in one image with each channel being different color.

[homm]

You can't display a 7-slice image because of color space with 7 channels doesn't exist. Color information in some channels will contradict with information in other channels.

[wiredfool]

You're essentially talking about spot colors at that point. It's done in print, but obviously when rendered on screen it's a 3 channel image.

But it doesn't really matter because there's no support for more than 4 usable channels in pillow.