But as we already know, that would be true only in a world where a cyan ink reflects absolutely no red from white light (same goes to magenta with respect to green, and yellow with respect to blue). Those unaware of classic printing problems might think that using RGB or CMYK to describe image color is irrelevant, because we can establish certain “symmetries” between color described in each system in fact, applications that handle color in a primitive way use the rule “CMY is one minus RGB”, in the sense that a primary color in one system is opposite to a primary color in the other one. Why is it better to postpone CMYK conversion? This “experiment” shows us how a particular CMYK system bind us to a specific numeric description of color, which in general won’t be valid on another CMYK system. There’s no way (yet) to make sure colors shown in a browser are accurate, even with a calibrated monitor, unless web pages start to make use of color management, not only in images but in solid colors as well (see El color en la Web), although this simulation let you get an idea of the relative differences among systems. Notice: colors shown here are close to printed ones in each system if you have your monitor properly calibrated and it closely matches sRGB standard. Epson 4800 on semi-matee proof paper, according to measurements on a real printer.Tektronic Phaser III print, according to its data sheet.European Standard for coated paper (Euroscale Coated), version 2.SWOP (Specifications for Web Offset Publications), version 2.Each one describes (“means”) a specific color in a certain printing system let’s take a look at what they “mean” in four selected and different printing systems: Top reason: current monitor technologies are quite similar main differences are due to different monitor settings, specially brightness and color temperature).įor instance, two different color patches are shown below. (In fact, RGB is device-dependent color as well, although we can expect more uniformity when seeing the same image in different monitors than looking at prints made in different devices. In color management jargon, a CMYK color system is called device-dependent color, meaning that if we want to talk about a certain color as represented by four percentages of four inks, this description is incomplete unless we specify at least three other things: the printing technology used, the ink type used and the media it will be printed on. Rule 2: If it is not possible to apply Rule 1, then DO NOT convert to CMYK yet.Ī reason to be so drastic? Certain issues with the CMYK system let me be more specific.Once we learn that colors in print will be ultimately described by means of some form of CMYK, we may get tempted to do our own conversions, because a) we know what we’re doing b) it’s not at all complicated as long as the converted image looks just right in my monitor c) I can save time to printer who needs CMYK images in any case.ĭespite of all that, I think it’s necessary to call for reflexion about this kind of processes, so I suggest to follow two simple rules for image RGB to CMYK conversion: In this category, the list tops with the famous (and no less uncomfortable) RGB to CMYK conversions. Nevertheless, some conversions may seem harmless if one judges them just for what we can see on a monitor screen.
Some types of conversion warn us about severe changes in the edited image: for instance, any conversion from color to grayscale. Bearing in mind that every color space has its own properties and limitations, this process should be done on an image very carefully and respectfully. Photoshop let us make “unpunished” conversion of images between color spaces. Next paragraphs are some thoughts about this and some rules that may prove useful. I think it briefly describes the core of the troubles we face when doing the type of conversion mentioned in the title.
#Rgb to cmyk image converter pdf#
I found this quote in an Andrew Rodney’s article in his website The Digital Dog ( Tips > March 2007: CMYK Part 1, look for a PDF just after middle of page).