What is the actual color space of film in film photography?

Question

I have been thinking about this question for a while now, and I haven't found an answer online.

Modern technology (scanners, screens, digital cameras, printers...) use technical color spaces to determine the colors they support and inform about the colors they don't support. We know that the human eye can differentiate over 10 million colors - so ten times more than this image composed of one million colors.

As an avid photographer of both digital and film photography, I am very curious to know if the "color space" of chemical film has ever been given a name, or if this would be too difficult (because it would be different for each brand of film? Or cannot be calculated very easily because it's dealing with molecules rather than data? Or maybe because color spaces are only for measuring digital data, not real-life chemical components?).

I would really like to know if any attempt at calculating the color range / color space (I might be using the expression "color space" wrongly here) of film has ever been studied and numbered.

Answer 1

I think it was the EktaSpace that was invented to hold all colors of films. Since silver halide color papers are still used as media for printing from digital, there are also color profiles of photographic papers floating around the Internet. See https://www.drycreekphoto.com/icc/ for examples.

These should give you some idea. As you can imagine, portrait film might have different color space than film for landscape photography. Another issue with hybrid analog/digital processing is that the colors of the film are usually tweaked in image editor and obviously, if the operator cranks up saturation here, the final colors will be outside of the film color space.

I think the print paper profiles are more important than film capabilities though.

Answer 2

I foud this graphic on photo.net, in a thread discussing the same topic:

I can't vouch for its veracity, but it looks reasonable. Both of the depicted films are a bit wider than AdobeRGB in the reds, but much shorter in green. But see the discussion on the next page, deeply saturatd greens require high densities and thus dark colours, which this chart doesn't represent well.

Answer 3

Today those of us not in the color reproduction industry as a profession tend to talk and hear a lot more about certain color spaces that a particular imaging device can or cannot support than our counterparts heard before the digital imaging age.

Saying an image device (such as a camera) supports a standardized color space means it is capable of producing all of the values within a particular color space. That's not the same thing as saying an imaging device is limited to only a particular color space. The same is true of photographic film. Often the color space available with typical display mediums (i.e. photo printing papers and the papers and inks for offset lithographic presses) is more restrictive than the color gamut of the film used for the source image.

For example, most DSLRs support both the sRGB and Adobe RGB color spaces. Since the Adobe color space is larger and encompasses more total color values than sRGB, it stands to reason that sensors which support Adobe RGB are capable of producing all of those color values contained within the Adobe RGB standard. When such a camera is set to output into sRGB color space the camera will only use the values within that color space in the images that it outputs. How colors that the camera has recorded that fall outside the gamut of the output color space are depicted within the output color space varies as well (E.g. perceptual vs. colorimetric rendering).

The functionality we refer to using color space designations with digital imaging has been around in similar forms for much longer in the printing/color reproduction/publishing industries. Different printing processes were capable of producing various levels of colors and tonal values. Even with monochrome (B&W) images, how many and how fine the tonal gradations a process can reproduce vary from one printing process to the next.

Just as a digital sensor may be sensitive to more color values than those used in the camera's chosen color space output, photographic film could also be capable of a greater range of color and tonal values than that of the media used to produce prints or other reproductions of the image captured on a film negative or slide.

Every film could have a different color space. Even different batches of the same film could vary slightly due to differences in manufacturing conditions and minute differences in the chemical makeup of the raw materials used to make them. The same is true to a lesser extent with digital sensors. No two sensors have the exact same sensitivity. In fact, each sensel (pixel well) on a sensor has a very minute response variation from the others on that same sensor. The difference is usually even greater from one sensor to the next, and increases again for the "same" sensors produced from different silicon dies. That's why part of the manufacturing process of digital sensors is calibrating each one.

In general terms, what process one used to develop the film could be an indicator of the overall capabilities of a particular film. The E-6 process used for most positive slide films results in a different "color space" than the proprietary K-14 process used to develop Kodachrome. Different processes following fixing and washing B&W film could produce different toning effects such as selenium or sepia. One could even process color negative film using the conventional B&W developer and get a monochrome negative. If, following the fixer, one used a hydrochloric acid and potassium dichromate solution and then exposed the film to white light one could then redevelop using color developer (C-41 or RA-4 process) to wind up with an unusual pastel color effect.

Using such different processes on the same type of film is somewhat analogous to selecting different color spaces for an image captured with the same sensor.

Answer 4

Before the current color systems there was the Munsell System of color notion developed by Albert H. Munsell. This is a three-dimensional, tree shaped arrangement. He prepared all the colors which can be represented using swatches over coated using pigments. The various hues are placed horizontal around a circle of ten major hues. This was followed by the CIE System developed by the International Commission on Illumination. The CIE Chromaticity Diagram was used by Kodak Engineers to show the limits of the three subtractive dyes (cyan – magenta – yellow) that deemed satisfactory for reproduction, color transparences and color negatives and color prints

Answer 5

CIC Chromaticity Diagram Color Map

Answer 6

It depends. (Don't you hate answers like this?)

For each kind of colour film, the manufacturer is obliged to find a complementary dye "set" to use in combination with each of the three different wavelength light sensitive layers R, G, & B. There is a direct comparison of photo optical process analogous to electromechanical imaging materials and processes too.

The combination of the three dyes is compounded to satisfy different conditions.
• It has to work (produce an acceptable colour image).
• It must be a unique set of dyes to comply with our international legal patent system.
• It must produce clean neutral values without objectionable colour contamination in the highlights, mid-tones, and shadows.

Obtaining the X-Y Chromaticity values for the dye set and graphing them on normal (or fancy colour CIE Chromaticity) graph paper shows the information you wish. The X-Y Chromaticity value is the graphical location of the "colour" of the pigment used in the reproduction process. You can look them up or get them from the manufacturer; some needing more persistence than others.

When you get the values, plot the points on graph paper and connect the dots to see the area enclosed by the lines. This is the gamut of the dye set.

Each different film has a different dye-set, and thus produces slightly different renditions from one another. Ektachrome has a different dye-set from Fujichrome from Anscochrome from Kodachrome from Gaevachrome, etc.

Each Pantone colour, paint, etc. has coordinates too. You can see on paper that some colours cannot be duplicated by some dye sets because they fall outside the limits imposed by the dye-set shape.

Having the coordinates of any ink, dye, or pigment allows direct comparison between/among them. Similarly, the coordinates are known for sRGB, Adobe RGB, The human visual system, and larger which can be used to determine how a process will (or won't) make you happy. Different sensor values are also available and sometimes actual production test specs for your specific piece of equipment.

Those relying on various colour reading equipment, spectrometers, colour management equipment, etc., take little comfort knowing that no two pieces of equipment agree according to extensive testing under controlled conditions by the Graphic Arts Technical Foundation/Printing Industries of America. Link to pia.org

Answer 7

Short answer first.

What is the actual color space of film in film photography?

There is none. The most accurate description of film colour space is that it is roughly tristimulus space. Film is not even reciprocal.

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Now long version.

Colour space is a mathematical abstraction. Colour space defines mapping between device values and percieved values.

It is not entirely correct to say that some camera (sensor) or film has a colour space because almost no camera's or film's behaviour is exclusively described with saying that it has colour space X. Not a single camera complies to Maxwell-Ives criterion (or Luther-Ives condition in other sources. I cannot find any good source to read about it except this one) and thus introduces some error on most of objects.

It is not correct to say that digital camera (sensor) X has gamut Y because the range of colours which camera outputs depends heavily on the processing used and may be of any size from black&white sized to XYZ. Whenever you hear that a camera outputs ProPhoto or say AdobeRGB you should keep in mind that it is said so only because of some processing software which decides it.

There is, indeed, some sense in saying that film X has gamut Y as long as you restrain the workflow to some standard. And even then the gamut will be mostly limited with printing technology, not with film. As soon as you make transition from analog to digital the gamut of film stops existing.

Output devices, on the other side, do have both gamut (the range of technically reproducible colours) and colour space (well-known mapping from input values to output values).

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