How does the colour printing process work with respect to the mask mathematically? (C41/RA4)

[Carriage]

I was wondering if someone could point me to a good resource or explain how the colour printing process works with the orange mask. As in, if you were to describe things mathematically, what does the filter pack do and does the paper compensate for the mask at all or does it invert "normally"? I've read that the mask is there due to imperfections in the part of the spectrum the dyes are sensitive to but the printing process doesn't allow for affecting areas separately as all changes are global.

 

[Photo Engineer]

The book Evans, Hanson and Brewer called "Color" IIRC, is an excellent description. Mees and Mees and James also contain descriptions.

Think of the mask as a positive image in color of the errors in the dye layer that contains that mask. Thus, the magenta layer contains a positive image of the yellow imperfections lying over the negative magenta image.

PE

 

[Carriage]

Thanks. Are these the books you mean?
http://search.slv.vic.gov.au/primo-...h_scope=Everything&tab=default_tab&lang=en_US
http://search.slv.vic.gov.au/primo-...h_scope=Everything&tab=default_tab&lang=en_US

Do the filters in the enlarger result in the image projected having no colour cast and the paper inverts it or does the paper contribute to undoing the mask? I suppose there's potentially a difference between what ideally happens and what does practically.

 

[Mick Fagan]

I have, "Principles Of Color Photography" by Ralph Evans, W. T. Hanson, Jr. and W. Lyle Brewer Copyright 1953. I haven't gotten round to reading it yet, picked it up at the Box Hill Photographic Flea Market, would you believe.

I also have, "Principles of Color Reproduction" by J. A. C. Yule copyright 1967. He or she was, according to the book, at Kodak Research Laboratories Rochester New York. Picked this one up, as above.

I picked up some others at the same time, among them was this, "The Theory of the Photographic Process" This is an interesting book, on the spine the attribution is to Mees, but once you are inside there are a plethora of names for the various subjects. I don't have the year of this book as that page is missing, but the stamp inside says Mee (2ed), while another stamp gives a stocktake date of 5 Dec 1960.

I'm in Melbourne........

Mick.

 

[MattKing]

The components in the paper have a non-linear and inverted response to light colours, with the non-linearity related to the errors inherent in the paper.
The components in the film have a non-linear and inverted response to light colours, with the non-linearity related to the errors inherent in the film.
The mask compensates for both sets of non-linear responses.

 

[RPC]

Could you explain more precisely what you mean by non-linear.

If by non-linear you are referring to the dye impurities, the mask in the film does not correct for dye impurities in the paper, only the negative. The paper dye impurities remain uncorrected in a print as they do in a slide.

OP, there are necessary speed differences in the paper between the blue, green and red sensitive layers (related mostly to the nature of silver halide materials). The color components of the orange color of the negative, enlarger lamp, and enlarger filtration all add together to exactly offset the speed differences in the paper in a correctly balanced print.

 

[MattKing]

If by non-linear you are referring to the dye impurities, the mask in the film does not correct for dye impurities in the paper, only the negative. The paper dye impurities remain uncorrected in a print as they do in a slide

I think we may be differing on semantics.
The paper responds the way it does, and the mask is designed with that response in mind.

 

[Carriage]

OP, there are necessary speed differences in the paper between the blue, green and red sensitive layers (related mostly to the nature of silver halide materials). The color components of the orange color of the negative, enlarger lamp, and enlarger filtration all add together to exactly offset the speed differences in the paper in a correctly balanced print.

So, even though the compensation made in the paper is different between brands, they still compensate as it is at least closer and then you can fine tune with the filter pack?

 

[Sirius Glass]

Basically the negative does not have enough of the base color, therefore more is added than is needed. Then only the surplus is removed. So mathematically it would be similar to adding +10i [j for Electrical Engineers] and then -7i is removed.

 

[RPC]

Right. The orange color of the negative and the lamp color offsets some of the paper response, with the filtration picking up the rest. By trial and error, you determine how much needed.

There are other factors beside the brand that determine the exact filtration needed.

 

[Photo Engineer]

Thanks. Are these the books you mean?
http://search.slv.vic.gov.au/primo-...h_scope=Everything&tab=default_tab&lang=en_US
http://search.slv.vic.gov.au/primo-...h_scope=Everything&tab=default_tab&lang=en_US

Do the filters in the enlarger result in the image projected having no colour cast and the paper inverts it or does the paper contribute to undoing the mask? I suppose there's potentially a difference between what ideally happens and what does practically.

Yes, these are books you would want to read.

As for the mask and the paper, the paper is designed with a tungsten color balance + 50R + approximately the mask density . In practical terms, the red speed (cyan layer) is considered to be the base speed or "zero". The magenta is about .5 M and the mask density in green faster, and the blue is .5M and the mask density in blue faster. Thus, when you print with an average tungsten enlarger, a 50 R and a negative, the image is just about balanced. Tweaking is really what you do.

Since all films are balanced to their respective light conditions, (daylight or tungsten) they should all print using the same pack of filters, and I have done so using film up to more than 60 years old as well as modern films and they look fine with just a tiny tweak to bring them in.

PE

 

[falotico]

For a book that is available online you might look at J.S. Freidman's "History of Color Photography". Chapter 19 deals with masking.
Here is the link:

https://archive.org/details/historyofcolorph00frierich/page/273

 

[Rudeofus]

Since typing formulas is a pain in anything but LaTeX, I decided to write my view of this into a PDF. This is how I would mathematically describe an orange masked color negative.