Color problem with homeade print

First question: What type of printer did you try to print on?

Second question: Did you create the image using CMYK color space? If the images are being saved into RGB colorspace you might not get a *good* color matching when you print out the image. But again this depends on the printer being used.

Third question: When you bring the image into a photo editing program, did you look to see what the value of the two blues when looking at the RGB or CMYK color values? They might just be way to close in color, and as a result dont print very well on that printer.

The blue on the side of the tokens is set to R:0 G:204 B:255, which is an unprintable color in CMYK color space (which, roughly, is what most color inkjet printers can print). So when you try to print it the printer driver converts that color to whatever it thinks is the best available approximation.

The dark blue on the drawings is R:0 G:158 B:234, which is CMYK printable (at least for some definitions of the RGB and CMYK spaces, which change from one device to another).

Now the main problem is that there's no sigle equivalency from RGB to CMYK, due to the fact that CMYK implies the use of inks wich are not the exact match of the theoretical CMY colors, and the intoduction of K (black) ink, mostly to compensate for that inaccuracy. And there are many ways to translate part of the RGB color into K, so there are many different equivalencies from RGB to CMYK.

To illustrate more clearly what is going wrong with your attempt to print this particular image, I opened the PDF file in Corel 12 and converted the RGB values into CMYK.:

R0 G204 B255 --> C66 M0 Y6 K0
R0 G158 B234 --> C81 M7 Y1 K0

As you can see, while there's still some difference in the values, it is smaller than in the original RGB values. Add to that the fact that differences among values in both RGB and CMYK color spaces are not always proportional to the perceived difference between colors (for instance, the 5% difference in the yellow values above is barely noticeable, even a 20% yellow on white paper might be hasrd to see).

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Yes, CMYK means Cyan, Magenta, Yellow, Black.

Theoretically, CMY should be the exact opposite of RGB. RGB means adding colored light to darkness, so no light means and full light means white. Different colors are defined by different amounts of each of the three basic additive (light) colors: Red, Green and Blue. Greys are equal amounts of the three lights; the higher the values, the lighter the grey.

RGB digital images are usually composed by three greyscale images, called "channels", one for each basic color (R, G & B). Grey value for each pixel in those images is usually expressed from 0 to 255, as most file formats accept 8 bits (256 values) of information per color channel, per pixel. 256x256x256 means 16,777,216 different combinations, hence the 16 million colors mentioned when talking about 24 bits (8bits x 3 channels) or full color RGB images.

When printing an image on paper, you're doing the exact opposite to adding light to darkness. You start with a hopefully white surface reflecting all of a supposed perfect lighting into your eyes. And the printed image will act as a filter to prevent some of the light to be reflected. Cyan ink will prevent some or all of the Red component in white light to reach your eyes. So if you print with cyan, you see cyan because the red light is absorved by the ink and only the Green and Blue components in white light are reflected. Same for Magenta with Green and Yellow with Blue. So if you print Cyan, Magenta and Yellow one over the other, no light should be reflected, and the printed surface should look black.

But real life isn't as perfect as theory. The cyan pigments do a lousy job as red light filters, thus printed cyan looks less cyan than it should, and C+M+Y, instead of perfect black, looks brwonish, because some of the red light still reflects and reaches your eyes. To compensate for this Black ink is introduced. As the cyan ink weakness affects all conversions from RGB to CMY, several formulas are used to substitute all or part of the CMY ink in the ideal conversion with K. There are different criteria to do this, and this isn't the place to enter into a detailed explanation of UCR and GCR. Suffice to say that one RGB color can be translated into several CMYK combinations, some with more K and less CMY, and others with less K and more CMY.

So, even though a CMYK is a 32 bit file, and a RGB file is a 24 bit file, the color space (the bunch of different colors) defined by CMYK is smaller than the RGB colorspace. There are RGB colors that just won't print in CMYK.

Inkjet printers from different makes use slightly different pigments, some (the "photo" printers) use two shades of cyan and two shades of magenta to compensate the limitations and widen the color range, and none uses the exact same pigments that offset printers use, so not all CMYK printers share the exact same color space. In spite of that, it's still impossible to print all RGB colors, so you'll be safer using CMYK colors when working with print as the final target.

When printing textures, the same applies: if your texture is in RGB, it will get converted to some sort of CMYK when printing, and some colors will suffer more than others. To avoid unpleasant surprises, convert to CMYK before printing. If you have Photoshop, you can use Gammut Warning (unde the View menu) when still in RGB to see what colors fall outside the CMYK color range. Lower the saturation a bit, use Selective color or Replace color under Image, Adjust to handle problematic colors, and once you have adjusted all out of gammut colors in your texture, convert it to CMYK. This gives you more control over how your texture will look when printed, otherwise, you're in the hands of Photoshop, Corel or your printer driver.

But most complex images like textures will convert just fine by lowering a bit the saturation while in RGB. Since Cyan is the more problematic ink, all colors using it are bound to be affected when converting: mostly blues and violets, greens to a lesser extent (this has a lot to do with the non linear way in which our eyes perceive color).

Enough already,

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