CMYK or RGB for CM Photo Printers

[hkellogg]

We are a university that deals with print production as well as photography. Students within the photography area utilize outside printing sources such as Walgreens, CVS, and Walmart. As a CM assignment, I would like to have the students profile these photographic output devices. While I know the printers are outside of our control and the results may not be accurate, I would like the students to understand the process.

My question is to the type of image file that would be used for printing on these devices. Do we use an RGB file or a CMYK file. We are using RGB with the photographic workflow. Is it the printer that would define the type of color model.

thanks for your imput.

Hans

 

[gordo]

We are a university that deals with print production as well as photography. Students within the photography area utilize outside printing sources such as Walgreens, CVS, and Walmart. As a CM assignment, I would like to have the students profile these photographic output devices. While I know the printers are outside of our control and the results may not be accurate, I would like the students to understand the process.
My question is to the type of image file that would be used for printing on these devices. Do we use an RGB file or a CMYK file. We are using RGB with the photographic workflow. Is it the printer that would define the type of color model.

Those photo printing facilities typically expect an RGB image with an embedded sRGB profile - pretty much the standard for digital point & shoot cameras that those places deal with. Rather than trying to profile the output, why not have your students test how the different locations deal with the same photo but treated differently. I.e. RGB untagged, tagged sRGB, tagged Adobe 1998, CMYK, greyscale, etc. Then correlate to how those images are displayed on the student's screen.
Also, some photoprint shops let you print your own pics - so how does that compare to the ones that do it for you? Also, some offer a different service for images that "have been manipulated on a color calibrated display" - see if there's a difference.

That IMHO would provide a great deal of discussion about color management issues.

best, gordon p

 

[Luc St-Pierre]

It would be wise to supply these printers with RGB files. The color models of these machines may vary from a CMYK model (C-LightC-M-LightM-Y_K-LightK or even extra green, orange etc.) The conversion will yield a wider gamut if RGB is used. Supplying a CMYK file (already shorter on gamut) is useless since these machine's PCS will then go CMYK to LAB to Private Model.

 

[hkellogg]

Thanks

Thanks

I appreciate the input.

I assumed that RGB would be the best color model but the idea of how each of these systems would handle the same image would prove interesting. Thanks for the idea.

Hans

 

[gordo]

I appreciate the input.
I assumed that RGB would be the best color model but the idea of how each of these systems would handle the same image would prove interesting. Thanks for the idea.
Hans

To be clear, not just RGB but sRGB.
And yes, it would be interesting to see the same photo submitted with a different setup. I.e. RGB untagged, tagged sRGB, tagged Adobe 1998, CMYK, greyscale etc. It would provide for a good discussion, especially if the students were also able to get some info about the workflow/equipment used by each vendor. I'd guess that the photolab workers don't know anything about how their color systems work.

best, gordo

 

[Stephen Marsh]

Rather than trying to profile the output, why not have your students test how the different locations deal with the same photo but treated differently.

An excellent suggestion Gordo!

Dan Margulis did a similar test and printed the results in the latest edition of his book, Professional Photoshop, 5th edition. Pages 306-310, Chapter 13, Figures 13.2, 13.3, 13.4 and 13.5. Both photo processing labs and commercial offset printers were tested.

I would recommend placing a synthetic neutral gray step and gradient wedge in some photos to help see what is happening with critical highlight and shadow tones and gray balance.

Disclosure: I own Dan's books and I am also a moderator on his Applied Color Theory list, however I have no business/financial association with Dan or his business partners.

Regards,

Stephen Marsh