8

This question is about the use of colors in professional printing.

I made the following table:

\documentclass{article}
\usepackage{xcolor}
\usepackage{colortbl}
\definecolor{rga}{HTML}{00E516}   % red-green gradient
\definecolor{rgx}{HTML}{19E700}
\definecolor{rgc}{HTML}{4AEA00}
\definecolor{rgd}{HTML}{7DEC00}
\definecolor{rge}{HTML}{B1EF00}
\definecolor{rgf}{HTML}{E5F200}
\definecolor{rgg}{HTML}{F4CD00}
\definecolor{rgh}{HTML}{F79B00}
\definecolor{rgi}{HTML}{F96800}
\definecolor{rgj}{HTML}{FC3500}
\definecolor{rgk}{HTML}{FF0000}

\begin{document}
\begin{tabular}{|cccccccc|}
\hline
$\Delta$ & $E_2$ & $P_1$ & $P_2$ & $P_3$ & $P_4$ & $P_5$ & $P_6$\\
$E_1$ & \cellcolor{rgj}11.18 & \cellcolor{rgi}10.66 & \cellcolor{rgj}11.23 & \cellcolor{rgh}9.90 & \cellcolor{rgj}11.39 & \cellcolor{rgi}10.72 & \cellcolor{rgh}10.26\\
$E_2$ & & \cellcolor{rgi}10.72 & \cellcolor{rgj}11.15 & \cellcolor{rgi}10.49 & \cellcolor{rgk}12.29 & \cellcolor{rgk}12.12 & \cellcolor{rgk}11.98\\
$P_1$ & & & \cellcolor{rgh}10.19 & \cellcolor{rgf}8.71 & \cellcolor{rgi}10.61 & \cellcolor{rgf}8.97 & \cellcolor{rge}8.47\\
$P_2$ & & & & \cellcolor{rgf}9.08 & \cellcolor{rgi}10.41 & \cellcolor{rgg}9.70 & \cellcolor{rgi}10.63\\
$P_3$ & & & & & \cellcolor{rge}8.22 & \cellcolor{rgd}7.70 & \cellcolor{rge}8.23\\
$P_4$ & & & & & & \cellcolor{rga}6.00 & \cellcolor{rgf}8.60\\
$P_5$ & & & & & & & \cellcolor{rgx}6.55\\
\hline
\end{tabular}
\end{document}

The pdf looks like this:

enter image description here

I could have probably automated the cell coloring, but this question is not about that.

It was printed on a conference poster, as follows:

enter image description here

I realize that using RGB colors was a bad idea, and that I should have used CMYK. However, I would expect some minor shifts (as in, e.g., Option cmyk for xcolor package does not produce a CMYK PDF), not that green would turn into blue.

The question is: is this amount of color difference common, or is this the result of some strange conversion by the print shop? Other colors on the poster (font colors, images) looked ok. Note that I can't ask them myself, because the conference offered free printing and I collected the poster at the conference registration desk. However, I would like to know if I can expect this again, and if yes, how to avoid it.

  • I wouldn't blame the RGB colors, the sRGB colorspace is standard and can be handled by every professional printer. The colors in your picture are reeeally far off and I'd blame the printing of the conference. To be sure you need the color profile of the printer to make a softproof. For normal paper I feel its not really necessary (when professional printers are used), but for other materials like canvas or metal (printing of photos for galleries), there are huge differences depending on the material. – thewaywewalk Aug 19 '16 at 8:56
  • 2
    This seems have nothing to do with LaTeX, but rather with low level of yellow ink in the printer. For exemple, the brillant red cell (11.18) is normally printed with CMYK printers with 100% magenta + 100% yellow. Here, in the photo, it is rather only magenta in the printed paper. Same for green: it's printed with cyan+yellow. If the level of yellow ink is low in the printer, you obtain your pretty cyan (6.55) cell. Here is a simulation with a image editing software in French interface (more cyan, less yellow): imgur.com/a/hDJQYMW – quark67 Nov 17 '19 at 4:57
  • @quark67 thanks for your comment, I think it answers my question. If you post it as an answer with the image you linked then I can accept it. – Marijn Nov 17 '19 at 11:11
  • There's lots of miss-information in the comments and answers to this question. It's not really a LaTeX question, but a general colour and printing question. The core problem is that the gamut (colour range) of RGB is much larger than CMYK. The RGB colours your have chosen cannot be printed in CMYK no matter what. They are too saturated. You need to do some reading on colour spaces and colour profiles and printing. LaTeX has no way of using colour profiles for converting RGB to CMYK. – David Purton Nov 18 '19 at 2:59
  • If you are printing professionally and care about colour, then the only real option for LaTeX is to work directly in CMYK. You can ask your printer for a destination colour profile and use a colour management aware application for your conversions from RGB to CMYK (e.g., Scribus or something from Adobe Creative Suite). – David Purton Nov 18 '19 at 3:08
4

This seems have nothing to do with LaTeX, but rather with low level of yellow ink in the printer. For example, the brillant red cell (with value of 11.18) is normally printed with CMYK printers with 100% magenta magenta + 100% yellow yellow.

Here, in the photo, it is rather only magenta in the printed paper. Same for green: it's printed with cyan cyan + yellow yellow. If the level of yellow ink is low in the printer, you obtain your pretty cyan (cell with value of 6.55) cell.

Here is a simulation with a image editing software, in French interface (more cyan, less yellow):

  • This has nothing to do with low level of yellow in the printer. Not all RGB colours can even be printed with a CMYK process. And conversion between the two colour spaces is exceedingly complex and depends on everything from type of paper, type of ink, printer characteristics, etc. If you have accurate profiles for you monitor and destination printer, you can get a reasonable approximation, but often you can not even rely on getting the same output from one print run to the next. – David Purton Nov 18 '19 at 3:04
  • @DavidPurton So, why does red and green in column P_6 became clearly magenta and cyan? I know that not all rgb colors can accurately being converted into cmyk color space, but this huge difference between pdf and printed colors is probably better explained by a low level of yellow color in the printer. Why is the cell (E1,P6) printed in light magenta rather in orange? Remainder: orange is light magenta + yellow in CMYK space. (By the way, English is not my mother language, so sorry if I made misconceptions). – quark67 Nov 18 '19 at 4:00
  • You can't trust what you are seeing. Already you have no idea what the printer has done when converting the RGB green/red to CMYK, then you have a scan or photo which has converted things back to RGB. The OP is printing professionally, not on a desktop inkjet printer. They aren't going to run out of ink. The only thing you can be sure of is that almost certainly any colour you see in your screen (which is always RGB) will look different when printed. – David Purton Nov 18 '19 at 4:10
  • My own tactic for choosing CMYK colours is to use a PANTONE CMYK guide and pick colours from that, then just ignore what they look like on screen since calibrating my screen is too hard. Even this isn't perfect, since different presses produce different output for the same CMYK colour. – David Purton Nov 18 '19 at 4:18
  • @DavidPurton your comment that "the RGB colours your have chosen cannot be printed in CMYK no matter what" is technically correct but seems a bit strong. I printed the table on my office copier (Xerox WorkCentre 7855) and the result is much better than the professionally printed poster. Red and orange are fine, yellow is a bit too dark, green is much too dark, but it is still green and not blue as on the poster. I don't know which conversion tricks or extra printing colors the copier uses to get this result, but clearly it can be done on an RGB PDF without extra manual color profile settings. – Marijn Nov 18 '19 at 8:55
7

As far as I know, the only reliable way to obtain exactly what you want on printing is to use the PANTONE colorspace, to which you have access through the spotcolor package under pdflatex, or xespotcolor under xelatex.

Here is a link to a Pantone colours palette.

  • Yes, but see my comment in the question: if yellow ink level in the printer is low, you cannot have a reliable reproduction of the colors of the PDF. – quark67 Nov 17 '19 at 5:06
  • And even then, the spot colour representation you see on your screen is merely an approximation to what you'll get at the printer. – David Purton Nov 18 '19 at 3:05
5

If you stick to pdftex or luatex (ie, not xetex), an alternative package is colorspace, which is simpler and more complete than spotcolor (caveat: I'm its author). It supports shades (ie, spot + black) and mixed spot colors, as well as ICC profiles for the default CMYK, RGB and Grey spaces (which is what I think you are looking for). It also supports the ! notation.

For example, for a spot color after loading the package just say something like:

\definespotcolor{mygreen}{PANTONE 7716 C}{.83, 0, .40, .11}

Then you can say \color{mygreen!60}. It also handles the internal PDF color spaces better than spotcolor.

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