How to add a spot color channel to a picture？

[826327700]

What are you trying to achieve?

How to add a spot color channel to a picture？like this in photoshop:

[lovell]

Did you see the composite operation? You can use it to layer an image containing a single colour with alpha over or under another image.

[826327700]

Did you see the composite operation? You can use it to layer an image containing a single colour with alpha over or under another image.

I don't think my problem is layer combinations. my quesition is a cmyk color mode picture needs to added a spot color channel when printing. emmmm,I don't know if my description is correct. My English is not very good.

I expect the feature to be like this: https://github.com/libvips/libvips/issues/1760

[826327700]

Did you see the composite operation? You can use it to layer an image containing a single colour with alpha over or under another image.

I don't think my problem is layer combinations. my quesition is a cmyk color mode picture needs to added a spot color channel when printing. emmmm,I don't know if my description is correct. My English is not very good.

I expect the feature to be like this: libvips/libvips#1760

I find a quesition same as me in stackoverflow: https://stackoverflow.com/questions/61608764/how-to-add-an-extra-channel-to-tiff-in-c-sharp-from-another-tiff-image his expected same as me. can sharpjs implement this feature?

[lovell]

Thank you for the extra context, I had misunderstood the original question, apologies.

The ifthenelse operation in libvips is not yet exposed in sharp but would make a good addition and a PR would be most welcome, if you're able.

https://www.libvips.org/API/current/libvips-conversion.html#vips-ifthenelse

The existing recomb operation might provide a suitable exanple as to how to implement this.

[muyichuanqi]

May I ask if it can be achieved now？