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My question is almost too unsophisticated for this site, but I need only a simple answer, not a perfect one.

I know if I create something that's blue, it might look darker (purple?) when it's printed.

I am looking for a very simple web-based tool (i.e., a URL), where I just type in an RGB, and it will display ON THE SCREEN a close approximation of what the color will look like when it is printed.

I don't care about lighting or surfaces or materials. I just want a crude, "What will this look like if I print it?" tool.

Even better would be if you could enter the RGB, and it came back with three columns:

  1. Here is the RGB you entered.
  2. Here is what that looks like on a screen.
  3. Here is approximately what it would like when printed.

I would expect a tool like this to show red kinda similarly in both representations, but some blues would look blue in #2 but purple in #3.

I think you get the idea. There are a million sites that can do 1 and 2 in two seconds. It's the "what would it look like when printed" part that I cannot seem to find.

Thank you!!

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    The problem is your screen isn't defined. So your screen has no profile therefore no simulation is possible.
    – joojaa
    Mar 3 at 15:50
  • Your best bet is probably to get Krita, convert an image to CMYK using an ICC printer profile (all available for free), or ask your printer for their printer profile. This at least will give you an approximate result, with emphasis on "approximate". For anything more accurate you'd need a hardware callibration device to profile your monitor and printer.
    – Billy Kerr
    Mar 4 at 10:46
  • Thank you all. I realize now that my question was naive, and more importantly, I have a bit of an idea now WHY it was naive. The person who demonstrated how one RGB color could result in multiple, very different looking colors when printed, was eye-opening. I did a quick test with Photopea, which someone suggested. For my purposes, it is sufficient.
    – David H.
    Mar 4 at 13:23

3 Answers 3

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You wish to get a "simple answer", but I'm afraid it doesn't exist. I can't rule out that such a web tool exists, but I haven't seen one.

One of the main reasons people in the print industry use Adobe software is because of its CMS (Color Management System) which is accurate and consistent. The only way Adobe can convert RGB colors to CMYK and preview how they would look printed according to a given standard is because of color profiles.

Color profiles are made based on physical tests. It's not just a mathematical formula. So to preview some RGB color "without any use of a color profile" doesn't really make sense. There has to made a connection between the physical reality of the light from the screen and the physical reality of the ink on paper.

I understand you don't want to go deep into stuff like calibrating your monitor, lighting, paper types etc. so I won't go into technical details, but just have a look at this quick example I made:

Here I'm showing RGB blue in the upper left corner and how that color would look printed according to 5 different color profiles (different regions and paper types). The resulting colors look vastly different.

Which one should such an approximating tool show? An average of sorts? Then someone would have to make a lot of decisions for each and every color about which profiles to include, how they should be weighted, which conversion method to use and so on. Effectively they should make some kind of averaged color profile. Additional inaccuracy would come from neither being able to trust the calibration of the user's monitor or the browser's way of handling colors.

It's possible to make an approximating tool like that I guess, but it would be a lot of work just to end up with something that's unusable for designers anyway. I can't personally live with not knowing which of these two colors my RGB blue would be converted to:

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There are two options.

  • The "pro one", getting a physical calibrator (hardware), a "pro" monitor, a calibrated environment (yes, the environment also should be "calibrated"), calibrated prints, pro software that simulates the result... Yes, it is difficult even for designers that work on this every day.

  • The normal real-life solution: Print a test chart like this:

https://otake.com.mx/Color/RGB-01-Letter-LowRes.png

On the specific print shop you are currently working, or in your office or home, and then, use it as reference.

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A free online option exists. It's Photopea. It knows one CMYK print process color profile and can show a prediction what it would output.

Start a new image. Let it be in CMYK color mode. You can make with the color selector a RGB color and paint something with it. You can for example select the brightest and strongest RGB blue (r=0, g=0, b=255) and paint with it.

The result on the screen is a dark low saturation blue - more like dirt when compared to the selected bright RGB blue.

When you select the RGB color you see what your computer happens to bother to show to you. The numbers r=0, g=0, b=255 surely get inputted right, but you see in the color selector what your operating system and your monitor bother to show to you. You'll see the right sRGB color space blue only if your monitor or display controller is color calibrated (the controller can be programmed to compensate color distortions in the monitor) and your operating system is NOT programmed to generate varied colors. Its quite easy to make some random color adjustments to the operating system for example to get brighter colors for one's favourite games.

Photopea knows only one color profile for CMYK printing. The documentation says it's SWOP.v2, but that's a vague definition because organization SWOP has published several profiles, each for different printing process. Maybe there's some patent or trademark problems. Or the implementation is not certified. I guess it's close to Webcoated SWOP 2006, but that's my guess based on comparisons of onscreen results. Let's call it SWOP.v2.

Organization SWOP was founded about 50 years ago to create printing standards for predictable printing results. See this https://en.wikipedia.org/wiki/Specifications_for_Web_Offset_Publications.

When you draw to a CMYK mode image Photopea finds which of the SWOP.v2 printable colors is closest to your selected RGB color. Then Photopea calculates which is the same in sRGB and shows it. The result is an useful prediction if

  • your system does show sRGB colors as the definition of the sRGB concept says and
  • you really are going to use a print shop or printer which obeys just SWOP.v2 color profile and
  • the final conversion to CMYK is made so that the out of gamut RGB colors are converted to printable CMYK colors in the same way as Photopea does it. Color profile SWOP.v2 doesn't tell how out of gamut colors are handled because it happens in your program, not in printing. Photopea at least doesn't turn the brightest RGB blue to purple. That's fine, but its proves that Photopea knows nothing of the computing+printing processes which output purple on the paper, when the intial RGB input was r=0, g=0, b=255.

To help staying in printable colors you can check option CMYK gamut in the color selector. It shows selectable, but unprintable colors as grey:

enter image description here

There's also a few random brush strokes made to a CMYK image with the brightest RGB blue.

If you use only in-gamut colors you do not have the problem "what happens to my bright RGB colors". Many of us make the paid design work in that way.

Summary: Hopefully you now see that you didn't ask anything simple. The exact asked system "input RGB, output on the screen what CMYK printing would produce" cannot exist! There are too many variables

  • in different CMYK printing processes and
  • in graphic programs which convert RGB colors to CMYK.

Adobe has been able to collect millions after millions year after year with programs which know and take into the account a reasonable number of those variables - assuming the user also knows what he does.

About the advertisements in Photopea:

Photopea tries to earn money by advertising. 1/3 of the screen is filled with varying ads. One can start to pay rent to get the ads turned off.

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  • Thanks for this answer. I have learned, through everyone's answers and comments, that my question really has no appropriate answer, and why. Nevertheless, this suggestion was a good one, and in addition, came the closest to answering my question in the way that I asked it.
    – David H.
    Mar 5 at 6:53

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