I´m generating a TIFF image for an hexachrome printer. The file has to be readable by Photoshop. I am filling the special/private Photoshop TIFF tag (0x8649) to embed additional information about the channels in a few Image Resource Blocks (IRB).
I would like somebody could confirm a couple of things:
Does Photoshop support Separated (TIFFTAG_PHOTOMETRIC=PHOTOMETRIC_SEPARATED) images with more than 4 planes?
If not, what I have done is creating a TIFF with extra alpha channels. Hence my next question:
In order to open the previous TIFF without losing information, is enough if I include the following IRB´s: 0x03ee, 0x0415, 0x041D, 0x042B, 0x0435?
I can include alpha channels color information in 0x042B, in RGB, HSB, CMYK, LAB,… alternate colorspaces. However, IRB 0x0435 contains information in LAB with DisplayInfo. What is the difference between these tags, and how does current color settings affect the alternate colors, if at all.
I have been working on project where external software embedded vector paths into JPG and Tiff and also embedded additional alpha channel into TIFF… It all worked in Photoshop and opened correctly. But that was year ago and would require me to spend something about an one hour to recall
Jarda:
Thanks for your answer.
My program is currently working, but I am not sure if it is as it is supposed to be. For instance, not sure if the IRB 0x0435 has to be always in LAB colorspace as my tests indicates, nor the relationship between this IRB and 0x042b. I´m always setting opacity to 0.
And the most surprising: Photoshop not being able to handle separated TIFF images with more than 4 channels.
I think with duotone color mode you can only get up to 4 channels.
And then you can have multichannel color mode and I think you can assign color ink to each channel and I think you can have as many as you want to or maybe up to 255.
Maybe you could reverse engineer a bit. Save multichannel PSD and see what is inside PSD binary. Or would it save TIFF too? Photoshop private tag is very very similar to what actually is in PSD file itself.
Jarda
Thanks for your help.
The moment I created a separated TIFF file with six channels, I moved away from it and started generation of CMYK TIFFs with alpha channels. After reading Adobe´s tech documentation I have begun creating 6-color TIFFs in Photoshop and doing reverse engineering, just as you suggested
I´m including the following IRB´s in the Photoshop tag: 0x03ee, 0x0415, 0x041D, 0x042B, 0x0435. There are just a few unanswered questions, though, such as:
1 - I can include alpha channels color information in IRB 0x042B, in RGB, HSB, CMYK, LAB,… alternate colorspaces.
However, IRB 0x0435 contains information in LAB with DisplayInfo. What is the difference between them?, and
2 - How does current color settings affect the alternate colors, if at all?
