# RGB to CMYK, then back to RGB... For the web.



## Seijun (Apr 28, 2009)

Hi all, 
My job where I work is to edit our company's product photos for the web (ebay). We make figurines, and the color is very important. I am not an expert at photo correction by any means. I get a lot of instruction from my boss, but am wary of his knowledge considering he still worries about whether or not the photos are "resized to 72 dpi". 
When I receive a photo it is in RAW, RGB format. My boss wants me to change it to CMYK before I do any color correction, then change it back to RGB when I am all done. He says CMYK has a great color gamut than RGB, gives me more control over what I am doing, is more accurate, etc, etc. I was under the impression though that CMYK is just for printing use..? Remember, these photos are purely for use on the web. Is it really best to switch the photos to CMYK before editing them?


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## Big Mike (Apr 28, 2009)

RAW files do not have a color space attached to them.  If you use Photoshop to open & convert the RAW image, you will then assign it a color space.  I don't know much about CMYK, but if you (he) is concerned about the gamut of the color space, I believe that Adobe RGB or Prophoto RGB are the ways to go.
Just make sure that you *convert* back to RGB.

Personally, since the final output is for the web, I'd just keep everything in RGB...KISS (keep it simple, stupid).

Understanding ProPhoto RGB


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## Seijun (Apr 28, 2009)

The RAW files are opened in Photoshop, yes. When I look at their "mode" in PS they are always assigned to RGB.


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## Big Mike (Apr 28, 2009)

> The RAW files are opened in Photoshop, yes. When I look at their "mode" in PS they are always assigned to RGB.


That's because they are assigned that during the conversion or that is just the default setting.  A RAW file on it's own, does not have it's own color space.  That how I understand it anyway.


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## Digital Matt (Apr 28, 2009)

Seijun said:


> He says CMYK has a great color gamut than RGB, gives me more control over what I am doing, is more accurate, etc, etc.



Sorry, but he couldn't be more wrong.  RGB is much wider than CMYK.  You should do all editing in RGB, especially since your final output is RGB.  People sometimes refer to CMYK numbers when color correcting, especially if the intended output is to print, but that can be done to an RGB file.  You can view the CMYK numbers in photoshop even in an RGB file.


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## Seijun (Apr 28, 2009)

I was kinda thinking that.. It seemed that when I converted to CMYK, edited, then changed back to RGB, the picture looked slightly worse overall, not better, than if I had just edited in RGB.. 

Along similar lines though.. I have been having a serious problem with the pictures in photoshop not transferring to the web accurately. A TON of color information disappears. To get the picture to display correctly online, I have to bump the saturation up by 20. In photoshop the picture will then look horribly oversaturated, but on an internet browser it will look fine (JPEG format). If, however, I change the pic to CMYK, then back to RGB, THEN color correct, then save as JPEG, the picture will look the same in photoshop and in the browser. Can anyone explain what is happening there?


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## Big Mike (Apr 28, 2009)

It sounds like you were missing the 'conversion' step somewhere.

When you take and image that is in a color space other than sRGB and display it on the web etc...the software just takes the numerical color values and displays them.  But because the numerical values are different for different color spaces...some of the colors can get messed up.

When you are in Photoshop and you convert from one color space to another, it reassigns those numerical color values to the closest color match...so you might loose some color info when going to a smaller gamut...but it's likely that you won't be able to tell a difference just by looking at it.  So if you convert to sRGB before you upload, the image should look exactly the same on your monitor.  (I'm not 100% on this but that's how I see it)

Again, I suggest keeping everything is sRGB to avoid they problems.


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## Seijun (Apr 28, 2009)

@ Mike: Thanks for the tip, I will open in sRGB and see what happens. They were being opened in "adobe RGB". I know next to nothing about color spaces, so never even paid attention to that option when opening the RAW files.
EDIT: Yes! switching to sRGB worked! Thank you!



Regarding CMYK vs RGB....

Editing an RGB photo, saving, and comparing that to the same photo that was switched to CMYK, then back to RGB, then edited and saved, I see almost no difference (but if I compare a photo edited in RGB to that same photo edited while in CMYK, I do see a noticeable difference, and I dont like it--picture seems to flatten out overall when edited in CMYK).

RGB>edit>save
vs
RGB>CMYK>RGB>edit>save
= almost no dif

RGB>edit>save
vs
RGB>CMYK>edit>RGB>save
= noticeable dif

Does that make sense?


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## Big Mike (Apr 28, 2009)

That does make sense to me.  When you convert to a color space with a smaller gamut (like CMYK), you are probably throwing out some of the color information.  Then when you convert back to a larger color space, that information has to be made up...which is never as good as having it in the first place.  

So it would seem to me, that you should avoid converting down (RGB>CMYK) unless it's your last step and you are sending it to a CMYK printer.  Because if you do, you may have to convert it back up (CMYK>RGB) which is where you will have problems.

Are you starting to see the benefits of keeping it in sRGB right from the start?

If you really want to use the best possible workflow...then you would want to start with the widest color gamut (probably Prophoto) and keep it there until you are done editing and ready to output the files...then convert it to your desired color space, in this case sRGB.  
The differences might be very slight, if they are even noticeable...so that's why I often suggest keeping it simple with sRGB all the way though.  But it's up to you to decide your workflow.


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## bhop (Apr 28, 2009)

There are zero reasons to convert to CMYK for web only.  CMYK is for print.  As you're finding out the hard way, it only creates color problems when you convert it back to RGB.  As Big Mike said, start in sRGB and keep it that way throughout.

also.. as far as resizing to 72dpi.. It doesn't matter as long as your pixels are the size you want.  That's something from the old days of web design, not relevant anymore.


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## Pat6100 (Jun 22, 2011)

New to site...tagging along on the subject's periphery: I suspect a retoucher we hired may have saved down our 16-Bit RGB Masters to 8-Bit CMYK. How can I detect if he changed them back to 16/RGB? Using CS4 and Bridge...didn't know if there might be any telltale clues in the Metadata or other panels, or anything that would show the lesser amount of info floating around in a 16-Bit bucket. Any help is appreciated!


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## jritz (Jun 22, 2011)

bhop said:


> There are zero reasons to convert to CMYK for web only.  CMYK is for print.  As you're finding out the hard way, it only creates color problems when you convert it back to RGB.  As Big Mike said, start in sRGB and keep it that way throughout.
> 
> also.. as far as resizing to 72dpi.. It doesn't matter as long as your pixels are the size you want.  That's something from the old days of web design, not relevant anymore.



Finally a sensible answer about why you would use CMYK!  Most photographers only use RGB because of fact that most photo printers (Epson, HP, Canon) take RGB input and convert to CMYK.  That is unless you are doing commercial work, then the process changes.


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## Bynx (Jun 23, 2011)

Being a graphic artist in the printing business Ive always used CMYK. I think its much better for color corrections since you are dealing in the 3 primary colors and Black. In RGB to alter the yellow you also alter the blue since you are changing the Green. In CMYK you want to alter the yellow then alter it. Blue, just alter it. All done separately. Now if there are any changes after converting back to RGB for web use might be a problem as noted by Seijun. Maybe the difference is whether you save it with sRGB or Adobe RGB. One is for web and the other is for printing.


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## Helen B (Jun 23, 2011)

Seijun said:


> ...He says CMYK has a great color gamut than RGB, gives me more control over what I am doing, is more accurate, etc, etc.



Take a look at this:







It shows the relative gamuts of sRGB and one of the most common CMYK spaces. sRGB is much bigger, with three times the gamut volume of the CMYK space. (There are, of course, other CMYK spaces. Many inkjet printers have a larger colour space than web offset.)

Editing in RGB isn't any harder than editing in CMYK once you know the colour wheel (Yellow is minus blue, cyan is minus red, magenta is minus green etc.). For cameras and monitors the relevant primaries are red green and blue (the additive primaries), not cyan, magenta and yellow (the subtractive primaries).

If you want colour accuracy, consider profiling the camera with the light source you use then don't mess with it after applying the profile (apart from converting to sRGB, which may mess with the colour, but that's another issue). Which Raw converter do you use? Which monitor profiling system do you use?

Best,
Helen


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## Peano (Jun 24, 2011)

Seijun said:


> He says CMYK has a great color gamut than RGB, gives me more control over what I am doing, is more accurate, etc, etc.





Digital Matt said:


> Sorry, but he couldn't be more wrong.  RGB is much wider than CMYK.  You should do all editing in RGB, especially since your final output is RGB.



Exactly. This will give you a visual idea of how much smaller the CMYK space is than the RGB space. When editing color in RGB, you can use sample points and set them to read out CMYK values (for adjusting skin tones, for example). That is sometimes a useful technique. But you should not convert to CMYK unless you are preparing an image for a printing press.


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## Helen B (Jun 24, 2011)

Remember that there is no single 'RGB space' and no single 'CMYK space' - each has to be defined by a particular space, such as sRGB or US Web Coated (SWOP) CMYK. Different RGB spaces and different CMYK spaces have different gamuts. It would be perfectly possible for one particular CMYK space to be larger than one particular RGB space.

It's difficult to represent the extent of a colour space in two dimensions, thus the use of wireframes and gamut volumes etc. If there are any sets of comparisons you would like me to make I can produce the diagrams for you (like the one I produced for my previous post).

Regards,
Helen


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## Peano (Jun 24, 2011)

Helen B said:


> Remember that there is no single 'RGB space' and no single 'CMYK space' ...... It would be perfectly possible for one particular CMYK space to be larger than one particular RGB space.



Don't slice and dice this with more precision than the case warrants. Given what the OP posted, the main point is that he should not ever convert an RGB profile (no matter which profile) to a CMYK profile for editing (regardless of which one), and then convert it back to RGB for web use. I can't think of any circumstances in which that makes sense. Can you?


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## Helen B (Jun 24, 2011)

Peano said:


> Don't slice and dice this with more precision than the case warrants. Given what the OP posted, the main point is that he should not ever convert an RGB profile (no matter which profile) to a CMYK profile for editing (regardless of which one), and then convert it back to RGB for web use. I can't think of any circumstances in which that makes sense. Can you?



I have already given a number of reasons why an RGB space is preferable  to a CMYK space and made the 3-D gamut diagram, so what's your problem?  Why do you feel the need to tell me what I should or shouldn't do? Do you believe that the OP doesn't deserve accurate information?


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## CCericola (Jun 24, 2011)

Helen B could not have explained it better. Just stick with RGB in this case. Now, if you were taking photos and putting them in a brochure to be printed in 4 color process then yes, the photos need to be edited in CMYK. 


This reminds me of an argument I had with an salesman. The client wanted flyers printed on the cheap so we found a 4 color process gang printer that would do them for pennies on the dollar. I get the file from their "designer" and it is in CMYK but I have a jpeg attached in RGB with a note saying "We want this neon green but it gets dull when we made the file cmyk" I said ok fine, it will cost more because that color does not exist in cmyk. The designer argued with me for days before I just took the loss and "fired" the customer. It wasn't worth it.


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## Peano (Jun 24, 2011)

Helen B said:


> Do you believe that the OP doesn't deserve accurate information?


No need to set up straw men and get defensive. I said what I believe:


Peano said:


> Don't slice and dice this with more precision than the case warrants.


That's hardly a call for inaccurate information.


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## mgilvey (Jun 25, 2011)

Bottom line; always start with the largest space you can which would be pro rgb or rgb or adobe rgb. sRGB is a destination color space not one you want your master files in. It is not as large of color space as the forementioned so you lose a little color by converting to it  I convert to sRGB for any type of desktop presentation including web. 

As mentioned cmyk is for print, another destination color space. 

There are also plenty of printers that want sRGB files but again. This is a destination color space not one you want to work your magic in. 

Working only in CMYK makes sense when you need to refine what converting loses and you will know how the colors will print. But never go back to RGB from CMYK--it's almost pointless.

Also realize that even if your monitor is calibrated. Web browsers each have their own way of interpreting color or so I read a few years ago.


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