I display inverted color images on my screen and re-photograph them with a carefully aligned camera on C-41 negative film
Let's assume for a second, you can expose a strip of C-41 color negative film with an arbitrary light source. The minimum density you can achieve is, if you look at the characteristic curve in Portra 400 data sheet, somewhere around (Dred = 0.2, Dgreen = 0.7, Dblue = 0.9). This is exactly the orange mask you see in unexposed and correctly developed Portra 400, and it's the absolutely brightest you can get. If you want this brightest color to have a neutral hue, you need to expose, such that Dred = Dgreen = Dblue = 0.9, i.e. a uniform gray strip with D = 0.9 will be the brightest neutral color you can create. With extra exposure you can then reach all colors in the range (Dred = 0.9, Dgreen = 0.9, Dblue = 0.9) + (ΔDred, ΔDgreen, ΔDblue) with ΔDred ≥ 0, ΔDgreen ≥ 0, ΔDblue ≥ 0.Hmm ok, so what you are saying is that I could get rid of the orange tint in my proposed way, but would end up with a kind of grayish overlay on top of my colors? And over exposing alot or other extreme measures will not change that ever?
Thank you very much, now this is an answer that was very useful and interesting!!Enough math babble: the best you can get is something which looks like a color correct image on top of an ND 0.9 filter. This might be interesting from a theoretical standpoint, but not really useful for projection. The mightly 1000W lamp of my Goetschmann projector would be reduced to a measly 100W light bulb with such a slide.
That's sort of the reason for the orange color in the first place - it's there to correct for unwanted adsorption of the cyan and magenta image dyes. http://www.brianpritchard.com/why_colour_negative_is_orange.htm does a nice job of explaining this.wanting to know if I could cancel out the mask the same way one can cancel out noise with headphones that apply 180° inverted sound waves.
You won't get a correct colour positive using orange mask C41 film
True, and you can actually still find that on Ebay.You would if you used Vericolor Slide Film SO-279! That's what it was designed for, and has a built in blue mask to complement the orange. Of course, it's long discontinued.
You would if you used Vericolor Slide Film SO-279! That's what it was designed for, and has a built in blue mask to complement the orange.
Hehe, nope, I still have >10 of the 135 size CN200. They are incredible hard to find but I managed to get the very last ones a shop had after searching forever.There is also Rollei CN 200, it is an unmasked color negative film. Available in maco but only in 120 format.
This is not an accident, but the main reason for using an orange mask: to create three independent characteristic curves in lock step with a constant offset. With all the other requirements imposed on film dyes (archival stability, high color saturation, ...) orange masked film seems to be the only technically feasible way to go.I have been thinking about the orange mask lately, and I noticed something in the characteristic curves for C-41 negatives. It looks like the three curves are offset from each other in a vertical direction, and it also looks like the offsets are simple vertical offsets.
If so then it should be possible to compensate for the orange mask by simply illuminating the negative with a compensating filter, i.e. a light source whose spectrum compensates for the orange mask.
I have been thinking about the orange mask lately, and I noticed something in the characteristic curves for C-41 negatives. It looks like the three curves are offset from each other in a vertical direction, and it also looks like the offsets are simple vertical offsets. Given that density is a logarithmic function, then if it is true that the characteristic curves are simply offset from each other in the vertical direction, then on the transmission scale it means that they are related to each other by a simple multiplicative factor. If so then it should be possible to compensate for the orange mask by simply illuminating the negative with a compensating filter, i.e. a light source whose spectrum compensates for the orange mask.
A corollary to this is that if one simply multiplies each of the color channels in a scanned image by channel-dependent constants that should also simulate the effect of using a filtered illumination of the negative.
On the other hand, if the vertical curves are not simply offset from each other by constant amounts then this scheme won't work.
but do not think that you will ever be smarter than the photo engineers at Kodak, Fuji, Ansco, Agfa, ... et al and all the scientific research that they conducted.
If color negative film could have been corrected without the orange mask, then the film would have been made without the orange mask. Kodak and the other companies did not add the orange mask based on the face that appeared on their morning toast, the orange mask is there because it is needed. If one wants to experiment removing it and printing as a learning experience that is all well and good, but do not think that you will ever be smarter than the photo engineers at Kodak, Fuji, Ansco, Agfa, ... et al and all the scientific research that they conducted.
Those people were amazing. I couldn't believe the complexity of the orange mask issues when I first read about it. The unwanted dye errors, the masking couplers, the resultant orange cast. It's sad that this technology has fallen away.
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