What's the Point?

The colour management ideal is to be able to move an image through the complete input/output process maintaining accurate colour without having to edit by hand at all.

The basis of the colour management of input devices is the profile. As with printing, a profile's use is limited to a single set of conditions.

There are questions to be answered as to whether it is necessary or worth following the colour management path with scanners and cameras. Maybe this can be answered if we look at certain aspects of these devices and how many profiles it is necessary to maintain. This document looks at this problem and attempts some sort of conclusion.

Generating a Profile:

Input profiles are often provided by the manufacturer, however this is not universal. If no profile is supplied and one is needed then it can be made. The same overall process is used to profile both scanners and cameras.

To make a profile, an electronic image of a known target image is produced. Software which knows what each part of the target should look like analyses the image and calculates the difference between it and the ideal. The correction factors are then combined into the profile.

Such a profile is normally called 'a custom profile' as it is specific to one device. A device's manufacturer will often provide a profile for use with the device but this will be generic and not take into account the variation which occurs between individual devices of the same type.

The scanner configuration dialogue for an Epson Flatbed scanner showing settings for both scanner input profile and the working colour space.

The RAWShooter Essentials Batch Convert window showing settings for both scanner input profile and the working colour space.

Applying a Profile:

To colour manage an image, it is necessary to 'assign' the device input profile to the unmanaged image then 'convert' the image to the working profile/space. (Note: The terms 'assign' and 'convert' are used here in a precise manner).

This may either be done automatically in the scanning software or done manually in a suitable image editor. For colour management to work properly the scanner should allow the setting of both scanner and working space profiles as in the example to the right.

Nikon film scanners currently perform the same operation automatically but can only use the device profile that Nikon provide themselves. To use a custom profile with any scanner which works this way, it is necessary to perform the profile application process manually in an image editor (if it allows) having turned the colour management in the scanner off first to ensure the scanned image is produced in an unmanaged form.

A RAW image from a digital camera can be treated in the same way except that the profile application takes place in the RAW converter. Adobe Camera Raw, at the time of writing, does not allow the direct application of a custom camera profile to an image. Various other RAW converters do allow this, notably the free version of RAWShooter. If it is important to be able to profile a RAW image then this would be a good method of doing so.

Scanners and Cameras

Flatbed Scanners

If the scanner is capable of producing constant lighting conditions, as a good one should, and the source material is pretty constant then a single profile will be all that is needed and, if the scanner configuration allows the use of an input profile, it is worth using one.

When scanning using a flatbed scanner with a transparency adaptor, it should be treated in the same way as a film scanner.

Film Scanners

The source material is variable - individual profiles are needed for individual film types whether negative or positive, a profile for Ektachrome 400 may not be good with Ektachrome 200 and certainly will not be good with Fuji Provia. Kodachrome can be a nightmare!

Digital Cameras

The variation in lighting will dictate individual profiling on a per-shoot basis. When shooting where accurate colour is critical (eg, photographic copies of art, museum pieces or modelling assignments) individual profiling is sensible. Where lighting and subject are frequently changing or where colour is being determined by the user then profiling is less necessary.

Conclusions

Whether to profile camera output or not...

Theory would dictate that accurate colour is more attainable if one colour manages using profiles. This, however, cannot be achieved without some effort so whether one profiles or not has to be worked out by the circumstances.

If the results are critical then colour managing image input is a good thing to do. On the other hand, if the approach is one of personal interpretation with changes being made to colours and gamma, then profile-based colour correction is likely to be a waste of time.

A profile is a specific piece of code which can be applied correctly in only one set of circumstances. If those circumstances are constantly changing then it becomes increasingly difficult to keep control of the colour management process.

...and the scanner?

If it is easy to set up colour management on a flatbed scanner for reflective scanning, it should be done. For film scanning it is less clear. If all the film scanning is being done on one type of film and lots needs doing then it may reduce the amount of work.

Decide on an individual basis...