Patrick Taylor

Digital colours (colors) etc.

Now that I have an A2 inkjet colour printer maybe I should understand more about colour management.

Color (colour) space

A color space (colour space) is an explicitly defined range of colours and luminances. In 1931 the International Commission on Illumination, or the CIE (from the French 'Commission internationale de l'éclairage') defined an all-encompassing color space based on human perception using averaged data from experiments conducted with a small set of test subjects. Even today this space – CIE 1931 – remains the standard reference used to describe all other colour spaces.

The CIE 1931 xy color space diagram has all the colours the human eye can see.

A screen or print displays less colours. How much less depends on the colour space used in its creation and it may have been passed through more than one.

From Wikipedia: The outer curved boundary is the spectral (or monochromatic) locus, with wavelengths shown in nanometers. Note that the colours your screen displays in this image are specified using sRGB, so the colours outside the sRGB gamut are not displayed properly. Depending on the colour space and calibration of your display device, the sRGB colours may not be displayed properly either. This diagram displays (or would display, depending on the device you are using now) the maximally saturated bright colours that can be produced by a computer monitor or television set.

Examples of colour spaces include sRGB (standard red green blue used for the creation of images for the web) and Adobe RGB (encompassing most of the colours achievable on CMYK colour printers but using RGB primary chromaticities on computer displays). RGB and CMYK (cyan, magenta, yellow and 'key' for black) are actually colour models.

Any .svg file is sRGB and contains less colours than the eye can see. Adobe RGB contains more (for example a .tiff file set to Adobe RGB) but still less than the human-visible CIE 1931 xy color space. Is it worth converting an .svg file created in Inkscape to Adobe RGB .tiff for printing? I don't know.

RGB is used on all modern screens. It is an additive colour model where white is the combination of all primary coloured lights, and black is the absence of light. CMYK is the opposite: white is the natural colour of the paper and black results from a full combination of coloured inks. The ink 'subtracts' from pure white. To save ink and to produce deeper blacks, dark colours are produced by adding black rather than using a pure combination of cyan, magenta and yellow.

It is important, however, to distinguish between commercial printing (where colour separation is used to make separate plates for cyan, magenta, yellow and black inks) and desktop printing on an inkjet printer with a different range of ink colours. Adobe recommends not converting RGB mode to CMYK mode for inkjet (desktop) printing:

From Adobe: Work entirely in RGB mode. As a rule, desktop printers are configured to accept RGB data and use internal software to convert to CMYK. If you send CMYK to a desktop printer it will apply a conversion anyway, with unpredictable results.

ICC colour profiles

ICC colour profiles are explained in detail here but unless you are a professional, it may be hard to understand (I am not a professional).

In simple terms, an ICC profile is a file that describes how a particular device reproduces colour. It describes the device's colour space. ICC profiles can be created for three types of device: a display device (monitor), an input device (a scanner or digital camera), or an output device (a printer). Generic profiles are created by device manufacturers – for a particular print paper for example. The profile is used by the printer but is specific to the paper, not the actual printer. You can also create a custom profile with a colour measuring instrument but in practice you would use one that already exists.

My PC Control Panel colour management setting identifies the device as Dell U2212HM (Analog) - Intel(R) HD Graphics 630 and shows the ICC profile with a DELL filename U2212HM.icm but also offers me those installed with my printers, or, amongst others, sRGB IEC61966-2.1, but I have decided not to mess with it. Perhaps I should, because image file colours on the monitor screen do not look exactly the same as they do when printed. At the very least, on the 'Advanced' tab I could calibrate the display.

ICM is an acronym for Image Color Matching. Files that contain the .icm file extension usually hold the color settings for a specific software application or computer device.

From Printers, monitors and scanners are devices that often use files with the .icm file extension. These ICM files allow multiple software applications, computer devices and even different computers to use exactly the same color settings so there is continuity between the way the colors are displayed when the file is opened and printed.

Page last modified: 11 June, 2021


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