When you’ve designed a beautiful artwork and are going to print it out with satisfaction, you may notice that the colors on the print don’t match the vibrant colors you chose on the screen, or don’t match the samples previously provided. What looks great on a computer monitor comes out completely different when converted to a physical print. What happens?
RGB vs CMYK
Printers and monitors output color in different ways.
The colors that we see on monitors, TVs, and digital cameras, we call screen colors, and they are based on the RGB display principle, which is red, green, and blue (RGB). All colors are made by mixing these three colors. RGB colors are additive, meaning they become brighter when you mix or increase their intensity.
The printed colors, we call them off-screen colors, are printed based on the CMYK principle. There are four colors: cyan, magenta, yellow, and key (CMYK), with the “key” actually referring to black, it is called K because it is the primary color used to determine the outcome of the image. These four colors are combined to form most of the colors, which we usually call 4C printing. CMYK is subtractive, which means that when they are mixed together, the colors become darker.
CMYK can only print 80% of the colors in RGB, and while most of today’s color processing software and printers can do the proprietary RGB to CMYK conversion for you, all colors are not 100% accurate.
This is when we introduce spot color. Spot color is a pre-mixed ink that, when printed, adds a separate plate to the printer, which inadvertently increases printing costs and reduces efficiency, made worse by the fact that some artworks have more than two spot colors.
Therefore, if you provide the printer with RGB colors and have strict color matching requirements, the printer can only use spot colors to print, at present, the common practice is a spot color + CMYK, the base color with a spot color, and the rest with CMYK.
Surface treatment
After printing, surface treatments are often required to improve the functional and visual properties of the paper, which results in varying degrees of chromatic change in the print. These changes are either physical (e.g., increased mirror reflection) or chemical (e.g., solvents in the ink react with the color). The most common type of surface treatment is lamination or oil-coating, both of which can be bright and matt. Obviously, when you coat with matt oil, the overall color will look darker.
Paper
Paper also plays a big role in printing. A bright white card will create a more vibrant color compared to kraft paper. Likewise, there will be color differences between different materials, the same artwork will have different effects on PE film and paper. The reason for this is that they absorb ink at different levels.
Moreover, even when printed on the same machine, color differences may exist from batch to batch of the white card, the whiteness, the humidity of the environment, the temperature, and human error in handling are all factors. But this error can be controlled to more than 95% similarity.
Other factors
Digital printing vs rotary printing, when sampling, for convenience, we usually provide clients with digital printing samples and will use this as a confirmation sample to follow up the bulk production, but in fact, they will be about a 10% difference between them. Because the inks used are different and the printing principles are different, the results are also different. Why not use rotary printing to make samples? It requires commissioning, a process that consumes a lot of paper and time, and disrupts production schedules.
Different monitors will also make the colors look different, cause their resolution is different, likewise, the phone and the monitor will look different. Windows and Mac operating system colors also look different since they use different system palettes.
Different software also with different performances. AI and PDF are preferred, but JPG and PNG are not used as a reference for color.
Suggetions
Color is subjective and everyone may have a different feeling. In practice, we can only try to get the colors as close as possible.
Designers should provide color options for on and off screen and provide Pantone color codes for color matching, just looking at the design on screen can be deceptive. As well as try to provide CMYK based artwork and transfer to printer in AI format.
Printing should use various correction tools, such as a colorimeter to determine color deviations, a gloss meter, and whiteness meter to address paper variability.
