Getting more accurate colour in your images

A common complaint with digital images is that an image might look contrasty, vibrant and sharp on the computer monitor but then appears flat, colourless and blurred when printed. The reasons for this are varied and not all of them can be resolved but it is possible to resolve some of these issues and anticipate others. Some solutions are cheap or even free others are very expensive. In this post I want to explain some of things that can be done to improve the colour accuracy of your images on screen and print. Colour management is a complex subject and this post is just scratching the surface. There are some links at the bottom wof the post which will give you more information if you want to go further.

Monitors

You should always try to view your display under subdued lighting which does not strike the screen directly. Large, bright coloured objects such as posters in the vicinity of the screen should be removed, blinds should be used in the windows to reduce glare. There are web tools such as this that can help the user to make simple adjustments to the monitor’s Brightness / Contrast settings. For more accurate colour, a hardware calibrator can be used, these can be quite expensive but will ensure your monitor is delivering its best. When used with the accompanying software the device measures the monitors ability to display ‘known’ colours that are displayed. The monitors success or failure to display these colours are recorded in a unique monitor profile. This is then used by the computers operating system to ‘ make sense’ of all colours that are displayed on it.

Monitor calibrator in use

Monitor calibrator in use ©Nigel Goldsmith

Printers

Cameras, scanners and monitors, capture and display colour using the additive Red, Green and Blue (RGB) colour system, while printers use the subtractive Cyan, Magenta, Yellow and Black (CMYK) system. These systems work very differently and not all colours translate between the two colour types.

Printers will deliver different quality prints with different papers and inks. With high quality, gloss paper the ink sits on the surface of the paper as it dries to produce sharp, bright detailed images. Highly absorbent papers such as cheap laser copier paper draw the ink into the paper, the colour and detail all blend together and produce ‘flat colour’ and blurred images. Quality matt or glossy papers when combined with good quality inks can produce high quality archival images. Printers are normally supplied with generic settings for different paper and ink types however, these are very rarely very accurate. Custom profiles can be created by printing out a target of known colours, a special device is then used to measure the colour patches and compare them to the colours that should have been printed. The software then creates a profile for that specific ink and paper combination. A new profile should be made for each type of paper or inks used. There are companies that create the profiles for you. You simply download the target (a digital image file), print it according to their instructions and then stick the printed target in the post, the company then measures it and emails you the profile for the paper ink combination you used.

Target used for calibrating a printer

Target used for calibrating a printer

Scanner / Cameras

Scanners normally operate in their own very controlled environment. The have a lid that excludes external light and use their own on-board, stable light source.  For colour critical work scanners can be calibrated by scanning a highly accurate IT8 target. The results are compared to the colours as they should be and a dedicated profile for the scanner is created.

Unlike scanners, cameras are designed to be used in a huge variety of lighting environments and while it is possible to use a target to get accurate colour for most applications it isn’t practical. An alternative solution often used to get accurate colours from a camera is to shoot a target such as the widely used ColorChecker below and then use an application such as Photoshop, Gimp or Elements to identify colour inaccuracy in the grey square. The software will then fix the colour cast and the correction can then be saved to be applied to other shots taken under the same lighting conditions.

ColourChecker used to check for colour cast at the start of a shoot

ColourChecker used to check for colour cast at the start of a shoot

Other issues

Most digital cameras offer the users two types of colour space, sRGB and Adobe RGB. The sRGB space was developed as a ‘lowest common denominator’ space, the group of interested parties that worked on it recognised that most users mainly view their images on screen and did not work with colour managed systems. It therefore makes all images look nice and bright (not necessarily accurate) on most types of viewing device. Currently sRGB is the standard colour space for images used online.

The other colour space is Adobe RGB, this contains more colours than sRGB and is a closer fit to the CMYK colour space used to print. On a colour managed system the Adobe RGB image will be richer and more accurate, it is not suited to screen use as most users will be viewing the images on un calibrated monitors.

If you are going to print your images you might consider Adobe RGB, colour can always be removed to create web friendly sRGB images. An sRGB image converted to Adobe RGB will not be as ‘full’ as an Adobe RGB image captured natively.

Monitors, cameras and scanners all work with RGB, printers use CMYK, each colour system has its own strengths and weaknesses however their are many colours that can only be displayed or printed in only one space so disappointment will always be hard to avoid.

Colour management in practice by JISC Digital Media

Colour Confidence suppliers of colour management solutions

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~ by Nigel on February 28, 2013.

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