VIDEO: How RGB Color is Converted to CMYK in Photoshop

VIDEO: How RGB Color is Converted to CMYK in Photoshop

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VIDEO: How RGB Color is Converted to CMYK in Photoshop
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I have been asked the question many times before: why does my photography/image look so flat when i convert RGB to CMYK color?

Well, the answer is science.

RGB is additive color theory. Red, green and blue light when combined produce white light. When red, green and blue light are turned off, there is no color therefore resulting in black. This is how your monitor and television function.

CMYK is subtractive color theory. Cyan, magenta and yellow ink act as filters to absorb and reflect light that is reflected off paper. When light reflects off paper where no ink is applied, this is white. When light reflects where all three colors are present, no light reflects back resulting in black. Cyan ink absorbs red light; magenta absorbs green light; and yellow absorbs blue light. This is the basic theory of subtractive color.

It’s important to note that a fourth ink (black) is used to create more contrast and deeper blacks/shadows in images. The amount of black ink is dependent on the conversion process that is used, for example medium GCR (Gray Component Replacement).

RGB color uses projected light which is much more brighter than light reflecting off a substrate with CMYK color. The additive light (RGB) creates a color gamut that is much larger than subtractive (CMYK) color gamut.

Does this explain RGB to CMYK conversion for you? Please place your comments below…

Transcript of Video

Hi. This is Rick Rys from HiDefColor.com. Today we are going to discuss the conversion from the RGB color space into the CMYK color space.

[0:14] RGB is an additive color space meaning that red, green, and blue light together will create white. When red, green, and blue light are off, they will be black when it is projected onto screen, or onto a monitor.

[0:31] CMYK is the subtractive color theory meaning that the cyan, magenta, and yellow inks act as filters. As light bounces off of the paper, it reflects up through the cyan, magenta, and yellow inks, which in turn will either absorb or reflect different color wavelengths.

[0:52] The opposite of red is cyan, the opposite of green is magenta, and the opposite of blue is yellow. The subtractive colors are the gray components of the additive colors meaning that when they’re put together, they create gray, or black, or white.

[1:07] The LAB color model–let me turn this off here–is a 3-axis color system, and the LAB colors are absolute meaning that the color is identical. It’s across what’s called a device-independent, meaning that the LAB color space is the only way for you to communicate different colors across different devices.

[1:35] Now, it is a 3-axis system. The first axis, the L-channel, or lightness goes up and down the 3-D color model, and it consists of white to black, and all of your gray colors will be exactly right down the center.

[1:49] All your neutral colors will be relatively in the center of this axis. The A-axis goes from a cyan/blue color across to a magenta/red color, and the B-axis goes from blue to yellow.

[2:07] Within this area, we’re going to plot our visual or reproducible colors based on the gamut or the profile of the device we have. I’m going to turn on the sRGB color profile. Most monitors display in sRGB; sRGB is preferred for any type of Internet or Web application.

[2:27] And look at this thing spinning here. And you can see the volume of the colors that you can reproduce from this additive color model. Obviously, since it’s dealing with projecting light, they’re very bright colors and they’re very saturated.

[2:44] Now when we bring in and display the CMYK GRACoL color profile, you’ll notice when I turn it on the sRGB encompasses the whole CMYK color gamut beside this area of cyan and greens through here.

[3:03] If you look down on the color model, you’ll notice that the circumference of the model is projected along the bottom here. You can see the outside perimeter of the sRGB color profile.

[3:17] The brighter colors are just not capable of being reproduced with the CMYK color gamut. You can see what happens when you get these real dark blues. There’s no blue for you to hit in a CMYK color model.

[3:30] What I’m going to do is I’m going to take our sRGB color profile, and I changed the opacity, so you can see the difference that we’re dealing with here. As you can see the volume of color on the RGB color profile is nowhere near what can be reproduced in a CMYK color profile.

[3:53] So what we have to do is we have to do our best job of remapping these colors, or what is known as tonal compression, to bring this sRGB color model into the CMYK color space.

[4:06] This is why–I’ll stop right here–when you look at a blue sky, you may always be disappointed with the results you get because when the photograph is in RGB, you’ve got all these deep bright blues and more of the colors you see in the horizon.

[4:30] When they’re converted to CMYK – you’ll notice when I change opacity, all those bright blues have to be condensed into this little area here of the blue hue that’s reproducible in CMYK.

[4:42] There’s a sacrifice there, and that’s where you get into using either relative rendering intent, or the perceptual color intent. That will help you resolve some of issues you have with converting your dark blues into the CMYK color space.

[4:58] Let’s turn this opacity back up, and you’ll get an idea, again, of what we’re dealing with here. We need to take all of this color and condense it into this little area right here.

[5:12] And this is the GRACoL color profile. The GRACoL color profile has more colors than the SWOP profile, so we’re going to get a better representation of some of those more juicier RGB colors when they’re converted to CMYK.

[5:27] So let’s bring this up again and show you the difference of converting all of this into this little area here. This is why color management is so important and knowing what profiles you’re dealing with.

[5:41] Your safest bet is using the sRGB color space and converting into the coded GRACoL profile. Keep in mind that dealing with your print provider, they will produce, or they will provide the correct color profile based on their printing condition.

[5:58] A profile is a recipe, or the characteristics of a particular printing condition. Based on the press, the inks, and the paper that they use that will produce a profile.

[6:10] Well thanks again for tuning in. I hope this clears some things up. If you have any questions, please feel free to leave a comment on the blog. And we will see you next time.

[6:21] Have a great day.

 
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    23 Comments

  1. Hey there! Do you use Twitter? I’d like to follow
    you if that would be okay. I’m definitely enjoying your blog and look forward to new updates.

    • Yes.

      The Twitter handle is @hidefcolor

      Thanks for the comment. That tells me I need to promote social channels more…

  2. Thanks!

  3. Thanks for the comments! As far as where house paints fall into these gamuts, look at the video ‘What is LAB Color’ on my channel. I don’t have specific paint colors plotted, but I do have a few Pantone colors plotted in the LAB color space. This is about as close as you will see how colors are plotted in the LAB color space…

  4. Wow, I always felt there was something “purple and green” about digital media, seeing the extended areas in the model it looks like those are the strong points. Also amazing as mentioned above – the small blue area that CMYK does better! I would love to see other models in comparison with these – like commercial house paint (bengamin moore lets say) and very fine art paint (holbein?) and what dimension fluorescents add. Thanks for the video.

  5. Wow, I always felt there was something “purple and green” about digital media, seeing the extended areas in the model it looks like those are the strong points. Also amazing as mentioned above – the small blue area that CMYK does better! I would love to see other models in comparison with these – like commercial house paint (bengamin moore lets say) and very fine art paint (holbein?) and what dimension fluorescents add. Thanks for the video.

  6. Hi, can I add photos to articles in indesign and then export the file as PDF for print without changing the mode? Thank you

    • Good question. Yes, I actually created a VIDEO on how to automatically convert all your RGB images to CMYK. Visit this link here and watch the VIDEO.

      This is one of my favorite shortcuts and saves sooo much time.

      Let me know if you have any questions…

      r

  7. hi, i know you will not be able to ansure that question,but what technically bothers me is,if rgb combined together creates white,then why does composite video and s-video also contains a luminance/white signal?,also b&w televisions only had 1 white bulb inside for white light,but color tv,s just can generate white light with r,g,b bulbs,pretty strange.
    anyway it blows my mind.

  8. Thank you! I wanted to present the gamuts as a ‘model’ that can visually demonstrate the differences in what colors are possible for each gamut; RGB or CMYK

  9. This is such a great resource. It makes so much sense to present the gamuts this way. Designers and artists are all visual learners and you’ve really broken it down for us!

  10. Thanks for the note. It was fun to make the video of RGB to CMYK.
    Do you have any other videos that you would like to see or explained?

  11. I was looking for a movie like that. It explains a lot, thanks

  12. Great job Rick! I teach color theory to art students. This video would be very helpful in explaining RGB/CMYK conversion to them. Is there a way I can get a copy to use in my classes? Source credit will be given, of course.
    thanks for posting this.

    • Thanks Jeffrey! The additive to subtractive conversion is really unique and now you can quantify the missing hues…I’m definitely open to sharing my resources with your students and bringing attention to the science of color.
      Rick

  13. isn’t it interesting that you have a CMYK color that doesn’t fit RGB!? i’m glad i was of assistance. good luck!

  14. Well, it seems we are on the same page here, so thanks for your assistance.
    I’m all calibrated (monitor and adobe suite), so that’s good.
    The issue is just plain coming down to the blue in the physical, printed samples I have matches the CMYK on my monitor, but there just isn’t a web-safe RGB that hits it right. I’ve trial and errored to a web-safe color that is probably close enough that noone will notice. If you look at 3:03 on your vid, that little tip of green-blue on top is about right.

  15. once you’ve previewed your color, you can now convert your image to sRGB through the ‘convert to profile’ option under edit menu. when you convert to sRGB, you want to select sRGB in the ‘destination’ drop-down menu and make sure you’re using the Adobe color engine and ‘black point compensation’ button is checked. you can adjust ‘rendering intent’ to see which one works best for re-mapping your out-of-gamut colors; relative works well. your monitor must be calibrated..

  16. i created your cmyk values in photoshop and assigned the US Web Coated (SWOP) profile. i was able to get a match with the sRGB color profile. if you’re making images for the web, this is the RGB color profile you should be working in. you can use Photoshop’s ‘proof setup’ option under the ‘view’ menu. select ‘sRGB’ under device to simulate drop-down menu and make sure ‘preview’ button and ‘black point compensation’ is checked. this will give you a preview of color.

  17. Never enough room in the comments for a real discussion, so I’m adding this: Would it play out to just work in the original CMYK profile, save the logos and icons as a JPG or PNG and just use them. On my screen, they look just right when I do that… but I don’t want to assume that they’ll look fine to everyone else.

    Again, THANK YOU! You’re the only person who’s responded to this question at all in the multiple places I’ve asked.

  18. I actually haven’t converted from anything. I just have a companies official color that is C-100, M-64, Y-0, B-23. I am trying to develop some web graphics, icons and logos to match and I just cannot get anything to match it. I have the CS4 Master Suite to work with. The original logo is U.S. Web Coated (SWOP) v2. So, is there an RGB color profile that I can use that will display that narrow band of the CMYK spectrum where the aforementioned color lives.

  19. what RGB profile did you convert to from CMYK? what CMYK profile are you working in? the profiles are extremely important to manage the color transformation. this will get you the best match. keep in mind that when you are converting color that are out of gamut, the rendering intent is critical to get the color back into the destination gamut. you will want to use either ‘perceptual’ or ‘relative colormetric’ to get accurate color.

  20. Thanks for the nice video, but I have a company logo that was designed to fall into that blue space where CMYK expands beyond RGB capabilities. It seems that no matter how hard I try to get a good color for the web (to match the blue I need), it is slightly too grey and flat. Any adjustments to try to increase the vividness of the color instantly causes it to go too purple or too green. The CMYK is 100,64,0,23. Any pointers on an RGB setting that will look right?

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