Why There Are Color Differences in Printing from your PC

By: Paul Curran

Properties

Most of you will have come across these three; Hue, Saturation and Brightness; if you have ever messed around with color settings of your images.

Hue: For example; blue, green and violet are all hues. They are colors. The dictionary definition of 'Hue' is; "the attributes of colors that permits them to be classed as red, yellow, green, blue or an intermediate between any adjacent pair of these colors."

Saturation: This refers to how vivid the color is. The higher the amount of gray relative to the amount of hue, the less vivid it will be.

Brightness: Relates to the relative darkness or lightness of the color.

In 1905 American artist A. Munsell published a color measurement system, naming the three parameters, Hue, Value and Chroma (Hue, Saturation and Brightness as above). This three dimensional relationship resulted in color identification in this format, for example; 7.5YR 7/12. Here we have a yellow-red hue tending with a value of 7 and a chroma of 12. There are 40 pages in the book covering all colors in the complete Munsell system.

Monitor and printer color production

Printer:
Printer colors are produced from inkjet cartridges emitting minute patterns of ink dots placed on paper.

All colors that you see come from just four colors; cyan (C), magenta (M), yellow (Y) and black (K).

As an aside, a mixture of cyan, magenta and yellow should produce black, but in reality a touch of black is needed to get it.

Monitor
A phosphor is a substance that emits light when subjected to radiation. Color phosphors are illuminated with electrons in your monitor and hence images are produced. There are three colored phosphors in each pixel on the screen; red (R), green (G) and blue (B).

Monitor and printer color differences

As will be aware, the printed output you receive hardly ever matches exactly that seen on your monitor 100% of the time. This is because the way that color is produced is different and the range of colors that are produced is different between the monitor and printer, as described above.

There are ways to get a closer match. You can experiment with printer driver settings or use image editing/color management software to help match up the two.

Printing Process

Most inkjet printers can't produce variations of the three primary colors so they employ a process called 'halftoning' to represent the thousands of colors needed. The two methods used for this are 'Dithering' and 'Error Diffusion'.

With 'dithering', different colored ink dots are aligned to give the appearance of neutral colors...suitable for large areas of color such as in graphs and bar charts. There are often additional settings such as 'Coarse Dithering'...for images with limited detail and shading, and 'Fine Dithering' for images with significant amount of detail.

If there is only text to print then 'No Halftoning' should be selected.

With 'error diffusion' inkjet cartridge dots are merged with surrounding color dots to produce natural colors with the possibility of subtle color gradation. Ideal for detailed images or photos.

When scanning, be aware that it will be more difficult to get a good match because the scanner will make the image using the CMYK data format, then RGB on the monitor and finally changed again to the CMYK data format via the printer.

Printers
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