Accuracy of color negative process

How accurate is color negative process?

There are too many factors involved in defining accuracy so let's narrow it down.

Suppose we want to reproduce a ColorChecker card photographically by illuminating it with a known light source, carefully exposing a color negative film, developing it in full compliance with C-41 process and printing the negative using RA-4 process (fine-tuning it until we get the best results). The accuracy is expressed as CIE color difference between the actual ColorChecher card and the print. The color difference metric is not critical but let's assume it is CIEDE2000. The ColorChecker card and the print are measured by the same calibrated spectrophotometer to reduce measurement uncertainty. What color difference values can we expect?

Disclaimer. This is a theoretical question with little or no practical significance (see Spherical Cow in Vacuum).

Reasonably accurate, but not quite exact. The differences between the reference and the final print will be obvious to the naked eye when compared side by side.
It is possible to get a little closer by applying some trickery to the printing step; notably masking and/or flashing.

Romanko said:

This is a theoretical question

Click to expand...

Which is the main reason I stopped worrying about it at some point.

koraks said:

The differences between the reference and the final print will be obvious to the naked eye when compared side by side.

Click to expand...

This is a good starting point. Can we define obvious as 2 or 3 times greater than Just Noticeable Difference (whatever it is in CIEDE2000)?

At the very least for some patches, while other patches will be very close or even appear identical.

koraks said:

Which is the main reason I stopped worrying about it at some point.

Click to expand...

I am afraid I haven't reached this point yet in my photographic journey.

At some point you'll meet your Yoda.

You can make it as precise as you wish or need. Not all RA4 papers are created equal, nor are all color neg films by any means the same. But under OPTIMIZED conditions (which can require a lot of experience to achieve), I'd put my money on the RA4 horse any day of the week over any current inkjet gamut.

The highest color fidelity I've ever achieved came from Portra 160 internegs generated from chrome sheet film originals, including appropriate supplementary contrast masking, and then printed onto Fujiflex RA4 media. Results were so good that I gave up my dye transfer printing experiments - the color quality standard of the past 70 years. But so much work and expense is involved either way that I far more often print Ektar CN film directly onto RA4 paper. The color quality seems to be light years ahead of what was stereotypical of chromogenic prints a few decades ago.

I taught color matching pros and had access to all kinds of fancy color spectrophotometers. But at the end of the day, there is simply no substitute for a trained color eye. I say "trained" because it takes a surprising amount of experience and understanding of color theory to rightly understand the interaction between physiological and psychological color vision. And then you still have to learn how specific films and papers potentially see hues different than we do.

But you're off to a right start with a MacBeth color checker chart under completely standardized conditions. Pay particular attention to whether the neutral gray scale really reproduces neutral, without any visible hue bias.

Next note the primaries (R,G,B) and secondaries (C,M,Y). When you achieved exact color balance, every one of those six patches should "sing" with the same intensity. None should dominate the others. They should have a mutual equilibrium. After that you can look at the tertiary color patches.

The MacBeth color chart is amazing well designed and manufactured. Their own illumination standard is 5000K, and their own light tubes match that. If you can't afford a serious light booth with high-quality bulbs, use diffuse sunlight. Beware of marketing BS claiming a high CRI from ordinary store bulbs. A serious color temp meter is a good investment for making standardized test negatives.

Just keep in mind that no color film or paper has ever been perfect; and none ever will be. You still need to learn the idiosyncrasies of each option and how to make the most of its own personality.

DREW WILEY said:

But so much work and expense is involved either way that I far more often print Ektar CN film directly onto RA4 paper.

Click to expand...

Yes, I meant direct print from the negative onto RA4 paper without masking or any other specialized printing techniques.

DREW WILEY said:

Pay particular attention to whether the neutral gray scale really reproduces neutral, without any visible hue bias.

Next note the primaries (R,G,B) and secondaries (C,M,Y). When you achieved exact color balance, every one of those six patches should "sing" with the same intensity. None should dominate the others. They should have a mutual equilibrium. After that you can look at the tertiary color patches.

Click to expand...

Thank you for these tips.

DREW WILEY said:

If you can't afford a serious light booth with high-quality bulbs, use diffuse sunlight. Beware of marketing BS claiming a high CRI from ordinary store bulbs. A serious color temp meter is a good investment for making standardized test negatives.

Click to expand...

The only light source I have is the Raleno video light I use for camera scanning. It is a "high CRI" variable-color LED source. It works pretty well in this application but I would not use it for color-accurate work.

I need to look into color analyzers and meters. I have an old X-Rite i1 with SpectraShop software which might suffice for now.

I did not intend to run the actual experiment with exposing the negative and printing it. I hoped that someone more knowledgeable and experienced had done it already but I could not find any published results. I am now wondering if it is worth doing.

Romanko said:

I did not intend to run the actual experiment with exposing the negative and printing it. I hoped that someone more knowledgeable and experienced had done it already

Click to expand...

A pro-printer I know who also teaches students does this exercise sometimes with a student. Put up a tripod somewhere in the work area, shoot a single 4x5" negative, develop it and then make prints of it, adjusting until the print matches closely to the captured reality. You can get close this way, but not without flashing the paper and burning & dodging. You can't get an exact match. I've not tried this myself, but I have a feeling he's probably correct. He's also got 30 years of printing fine art for photographers under his belt, which includes many prints that are held by prominent museums, so I figured I would just take his word for it.

Romanko said:

How accurate is color negative process?

Click to expand...

The question should be pòinted to yourself. Is the color negative process accurate enough for you? Do you like what you are getting? It is all that matters.

Scientific accuracy is good for film and paper manufacturers. Some lab professor told me: "you can't improve what you can't measure". So some qualitative characterisitcs are needed to define color and compare different tones when trying to reproduce a color image. But not really needed for a photographer.

halfaman said:

The question should be pòinted to yourself. Is the color negative process accurate enough for you? Do you like what you are getting? It is all that matters.

Scientific accuracy is good for film and paper manufacturers. Some lab professor told me: "you can't improve what you can't measure". So some qualitative characterisitcs are needed to define color and compare different tones when trying to reproduce a color image. But not really needed for a photographer.

Click to expand...

When I scan chrome film and adjust the colors in Lightroom, I don't verify if the resultant files match the original film. As long as it's pleasant and "right" to my eye, that's good enough. I trust myself enough to create realistic colors as I remember them and figure others will appreciate my final color selection and design even if they don't. After all, the original color palette of the film was designed by some engineer, maybe dead by now, who thought it was the right color palette - for him. Also, different films have different color characteristics deliberately designed into them to meet some preconceived artistic point or to give photographers various choices of palettes to start with.

Of course, negative film is different in that all the colors start out reversed. But the concept is similar. Unless you need results for advertising, and the colors have to match the actual colors of the clothes you're selling so buyers know what they're buying, for example, there's little reason matching for artistic reasons.

halfaman said:

So some qualitative characteristics are needed to define color and compare different tones when trying to reproduce a color image. But not really needed for a photographer.

Click to expand...

Alan Edward Klein said:

Unless you need results for advertising, and the colors have to match the actual colors of the clothes you're selling so buyers know what they're buying, for example, there's little reason matching for artistic reasons.

Click to expand...

I totally agree that absolute color accuracy does not matter in fine art and many other areas of photography except maybe some scientific applications and art reproduction but they gone digital a long time ago.

Learning the limitation of a given media is just as important as learning its possibilities. Shoot, print, shoot, print. Equipment like color analyzers only speeded up the workflow in commercial settings;
but they're no substitute for an experienced eye.

Don't underestimate the need to understand basic color theory. The MacBeth chart was designed with that in mind. Those color patches aren't random; they're quite effective in making discrepancies in a film or lighting setup stand out. But it's way better to expose any test negative of one in daylight than under a discontinuous LED spectrum. If you don't have a color temp meter, aim for "white" daylight diffused by clouds rather than under a deep blue sky or cold overcast.

Actual color printing is much easier and more predictable if you do practice these chords of the piano first. You'll save time and money.