Announcement

Collapse
No announcement yet.

RGB to CMYK problem

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • RGB to CMYK problem

    Hi All again,

    I saw a thread in a few days, about photo like this picture but I can't find it. When I changed this picture to cmyk (profil EuscaleCoated v2.). I've lost the detail of light at the upper right, as U see. I tried some other profile but it was the same. Can someone help to find the thread or to correct this problem, please?

  • #2
    Re: RGB to CMYK problem

    Hi Saby.

    I am not quite sure what you are asking for Saby.

    Are you converting to CMYK for a reason or do you just want to repair the blue cast?

    The red channel is damaged and that will make a damaged CMYK.

    It would be better to repair the damage before the conversion.
    I replaced the red channel with the green channel to repair the damage. This will then convert to CMYK without any noticeable loss.

    There are several methods to repair this (Search for ‘Scuba Diving’)

    Hope this helps.

    Ken.
    Attached Files

    Comment


    • #3
      Re: RGB to CMYK problem

      you can't just blindly convert to cmyk, you need to show the gamma warning first adjust accordling to remove the out of gamma portions of the image (hue saturation works.....) convert, and then adjust again in levels to get as close as possible to the rgb image.

      Because the color ranges are so different between the two, and rgb is basically what your monitor is, and cmyk would be the print version of the image, you will never be able to fully simulate cmyk onscreen.

      so, as stated above unless you are printing this image at an offset printing facility, or its required to be cmky for a client, leave it in rgb.

      Comment


      • #4
        Re: RGB to CMYK problem

        you can work on RGB mode but always put the preview in "WORKING CMYK" so if you will convert it to CMYK mode no data would be loss.. and by the way working in RGB is only good for video and web.. but for printing always use CMYK mode .. CMYK is easier to adjust because it has four channels

        Comment


        • #5
          Re: RGB to CMYK problem

          Originally posted by paroroonman
          but for printing always use CMYK mode .
          for offset printing, yes....but for desktop printers no...because your printer driver is set to convert from rgb to cmyk...if you send it as cmyk the will convert from cmyk to rgb back to cmyk and you can get some pretty muddy prints.

          Comment


          • #6
            Re: RGB to CMYK problem

            Originally posted by Cameraken
            Hi Saby.

            I am not quite sure what you are asking for Saby.

            Are you converting to CMYK for a reason or do you just want to repair the blue cast?

            The red channel is damaged and that will make a damaged CMYK.

            It would be better to repair the damage before the conversion.
            I replaced the red channel with the green channel to repair the damage. This will then convert to CMYK without any noticeable loss.

            There are several methods to repair this (Search for ‘Scuba Diving’)

            Hope this helps.

            Ken.
            It's not really accurate to say the red channel is damaged. The image is essentially blues and greens. By definition, there will be no red information. It is the lack of red that causes the heavy cyan cast, but if that is the desired color, forcing a duplication of green/magenta information in the red/cyan channel keeps detail, but the color shift creates an entirely new image. If the intent is to keep the colors, it's no solution.

            The real problem is that blues and greens take a heavy hit when moving from RGB to CMYK. Cyan is a weak ink, which is why you need 10% more of it to balance with Magenta and Yellow to create neutral. The tonal range simply isn't there. Any image that relies on varieties of blues and greens for detail will necessarily suffer in the conversion.

            The default conversion intent is Relative Colormetric. This will attempt to create CMYK duplicates of the original RGB colors, where possible, and where there are out of gamut colors, they just get crushed at the edges. Using Perceptual as the conversion intent will provide a precise replication of the relationships between each tone, though pulling the out of gamut tones into CMYK range will result in the entire image shifting color. Sometimes a channel from the RGB file (or perhaps even a greyscale conversion) can be copied into a layer atop the CMYK version, in luminosity mode, to help bring back some detail, but usually it's a toss-up between color and detail, and no solution will be totally satisfying.

            This is where the blue detail went: On the left, the blues and greens in a generic RGB profile. On the right, the withered remnants in CMYK.
            Attached Files

            Comment


            • #7
              Re: RGB to CMYK problem

              Hi Edgework

              Thanks for a great explanation of where the blue has gone.

              I have never been scuba diving but I was under the impression that most underwater photographers try to eliminate the blue cast (but I guess this mainly applies to close up shots)

              I do agree that this image looks better with the blue cast than without it though.

              I tried replacing the cyan channel with the red channel. This gives an even blue to the top right corner. But the only answer to keeping those colours is to keep the image in RGB. Attached is the gamut warning. It shows (in grey) the colours that will shift in saturation.

              Ken.
              Attached Files

              Comment


              • #8
                Re: RGB to CMYK problem

                Originally posted by Cameraken
                Hi Edgework


                I tried replacing the cyan channel with the red channel. This gives an even blue to the top right corner. But the only answer to keeping those colours is to keep the image in RGB. Attached is the gamut warning. It shows (in grey) the colours that will shift in saturation.

                Ken.
                Hold that thought. It's a valuable trick, but for precisely the opposite condition.

                Often, when converting to CMYK, an image that might already be somewhat deficient in Cyan will turn up in CMYK with a nearly worthless Cyan plate. Photoshop assumes a 20% dot gain for printed material when it moves colors into CMYK and lowers values accordingly in the quarter and mid-tones to compensate. Information that is already weak can get blasted into vapor in this process.

                The red channel is analogous to the cyan channel, minus the reduction for dot-gain and retaining the shadow detail that gets ciphoned off into the black plate in CMYK. There will always be more quarter-tone and mid-tone detail in the Red channel than in the corresponding Cyan channel.

                Enter the technique you tried. Copying the original red channel into the current cyan will bring back lost detail, and it will be actual color detail, not the forced compromise of substituting one plate for another. Usually it results in too much cyan, a much happier problem that can be treated with a quick curve.

                When everything looks sunburned and all shadows are hot, this is a good way to increase cyan. Even if you don't have an original in RGB, duping the 4c version and converting to RGB will to some extent reverse the dot-gain reduction, resulting in better detail than you started with.

                Of courses, this is only relevant if your end result is going to a printing press.

                Comment

                Related Topics

                Collapse

                • xxxmen
                  Converting CMYK to RGB and back to CMYK.
                  by xxxmen
                  Hello all,

                  I'm aware that RGB is a larger gamut of colours then CMYK. If I had an original image that is given to me in "CMYK" when using Photoshop for colour correcting; is there any loss in quality if I convert the CMYK image to RGB.
                  The reason for converting to RGB...
                  11-27-2008, 10:12 AM
                • ekuna
                  RGB or CMYK?
                  by ekuna
                  Should it matter to the retouching house if I work in
                  RGB or CMYK? You can always convert the mode - is it
                  such a big deal?
                  10-11-2010, 04:16 PM
                • D Thompson
                  RGB to Lab/CMYK and back to RGB
                  by D Thompson
                  I asked a question in this thread (http://www.retouchpro.com/forums/pho...s-lab-raw.html) about going from RGB>Lab/CMYK>RGB and got some good answers from Robert & John. I usually stay in RGB and will change the color sampler readout to CMYK when doing some...
                  07-26-2011, 11:04 PM
                • PehlaPehla123
                  RGB to CMYK Conversion HELP :-(
                  by PehlaPehla123
                  This images shows ok in RGB. When i convert it into
                  CMYK mode. Then CMY channel become too faded
                  (blurr, ghosty) and patchy but black channel looks fine.

                  Its my son pictures thre r so many pictures. Im feeling too helpless.
                  I hv work on ths images in CMYK mode....
                  06-13-2013, 07:08 AM
                • kl4
                  rgb vs cmyk
                  by kl4
                  hi all
                  I am new to the site and loving it!

                  I am avidly following up on and tracking down all references to extraction, masks and clipping paths. Most of what I have found so far has been very informative and interesting (some very confusing and way above my head on first reading)....
                  10-10-2005, 09:15 AM
                Working...
                X