Colour Management - How It Works

What are Rendering Intents?

When using ICC Colour Management aware image editing, processing and printing applications, such as Photoshop, Lightroom or Capture One, you will come across the term Rendering Intent. But what does it mean?  This article will hopefully give you a better understanding of what Rendering Intents are, and importantly, which one to use.

ICC profiles support four Rendering Intents. These define how the colour reproduction process should reproduce an image when using an ICC Profile, and importantly, cope with colours and tones which are outside of, or near the edge of the device's colour gamut, in order to achieve the desired colour 'rendering'.

When reproducing colour using a medium (paper and ink) with a smaller or different shaped colour gamut than the original photograph or scene, it is inevitable that some colours or tones may not reproduce accurately, appearing to be lost or degraded. These are said to be 'out-of-gamut'. Some subtle tones, particularly saturated colours and dark shadows, may be squashed, flattened together or 'clipped'. This applies to the tonal range, or density, as well as to colour hue and saturation. An extreme case would be an image of colourful flowers, etc. being reproduced in a newspaper with it's dull 'grey' paper, where the actual "density range' will be very low (lower than D1.2).

Even the best of today's inkjet printers and papers won't be able to reproduce all of the colour gamut that digital cameras can capture.

Clearly, compromises have to be made. The Rendering Intents do this, but in subtly different ways.
The four ICC Rendering Intents are: 

Colorimetric:

There are two of these: Absolute and Relative. To reproduce an image colorimetrically means having colours 'mapped' as accurately as possible. The downside is that distinct colours which are out of gamut may be 'mapped' to be the same, thereby losing detail by being 'clipped'. Dark shadow detail may well 'fill in', i.e. be lost. These colorimetric Intents are designed for use when the device (with suitable paper) used for reproduction has a large colour gamut, such as an inkjet printer.

This will map the white point of the image 'relative' to that of the original. The white point of the original colour space (often the Photoshop 'Working Space') will be matched to that of the output (typically a printer profile) and other colours scaled in relation. It can be used in proofing situations where accurate reproduction of the printing press 'paper white' isn't required. It is often used when printing digital camera images on suitable ('glossy') paper. In which case always use Black Point Compensation ('BPC'), in Photoshop, etc.
Although it is not as accurate as 'Absolute', Relative Rendering (but not with 'BPC') can be used in 'hard proofing' workflows.

Black Point Compensation:

In Photoshop this is found under Color Settings (where you should set your defaults) or under Edit / Convert to Profile (where you can select it when converting individual Images from RGB to CMYK for example), and under Print. It is used to automatically map the black point of an input (camera or 'Working Space' etc.) profile to that of an output (printer) profile. Typically the input colour space will have a darker black point than that of the output print. If Black Point Compensation is not used, the shadow areas could be filled-in, losing detail, in the reproduction. This feature is especially useful when using the Relative Intent. It should normally be left ON. Not available in Elements, Illustrator, etc., but is always 'on' in the latest versions (at least) of Lightroom.

Relative Colorimetric:

   Relative Rendering with 'BPC' /                           Relative Rendering without 'BPC'.

These two versions of the same shot show the effect of using Black Point Compensation (BPC). Your viewing of the differences will depend on your monitor and browser however! In the left image the effect of BPC can be seen in the tyre, particularly at the top left, which is no longer 'filled-in'. The saturated reds are also very subtly different.

Absolute Colorimetric:

This Intent should not be used be used in normal photographic reproduction, as it is intended for use in 'hard proofing' situations only, such as when making a proof to simulate a commercial printing press, such as an 'Offset' printing press. When proofing we typically have a larger colour gamut in the (typically) inkjet proofer than in the (usually offset litho) printing press we are simulating. So out of gamut colours are seldom a problem.
This will simulate the 'lightness' and colour of the paper 'white', by printing a 'tint' of that colour, if necessary. If the printed paper you are trying to simulate is a 'dull yellow' and the proofing stock is a 'very bright blueish white', it will print a very light tint of yellow (and probably magenta) in the 'white paper' background, and also throughout the image's tonal-range. Although being very accurate 'colorimetrically', some customers may question the appearance of the 'paper tint'. It will also do absolutely no compression in the dark tones/colours. We would not advise using this Intent for reproducing digital camera or scanned images as they will probably reproduce too 'flat' with very dark and often 'yellow' highlights. So for hard proofing only.

Perceptual:

This will attempt to render colours in a way which is natural to the human vision. The gamut of the source image colour space (typically a 'Working Space' or camera profile) is scaled to the output colour space (usually a printer profile). This will pull out of gamut colours into gamut. Colours at or near the edge of the gamut will also be pulled in to give a distinction between them. This will generally give a pleasing result. Different ICC-profiling software vendors achieve different results with the Perceptual intent. In particular, profiles generated with older software versions may exhibit a lack of saturation. For digital camera images you should try both Perceptual and Relative (WITH 'BPC'). Perceptual should usually be used for scans of colour transparencies, and often also gives the best results for scans from reflection colour prints. Not recommended for use in 'hard' proofing.

Please note that many of the characteristics of the Perceptual Intent (and also the Saturation Intent) are under the control of the Profiling software developer (such as X-Rite), rather than the ICC.

Saturation:

This will pull saturated colours out to the edge of the gamut, thereby increasing saturation, or colour 'strength'. It is intended to be used for vector graphics; i.e. logos, line-art, etc. Don't use it for photographs (except special effects) or for hard proofing!

Summary:

It's very easy to make a 'Rule' to use a particular Rendering Intent for all images, but it's probably much better to select the Rendering Intent on an image-by-image basis. Use the most suitable Rendering Intent to get the effect you want, ideally, while 'Soft Proofing' in Photoshop, etc.

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This page updated January 12, 2021