When you use an image editor like Photoshop or Gimp, you have a few color modes that you can choose to create the image. There’s greyscale, RGB, and CMYK. Normally, CMYK is used for images that are going to be printed, and RGB is used for images that will be published online. This has to do with how the colors are rendered and you don’t want to use an image in CMYK for the web as the colors may not look right. Photoshop supports both these color modes and it also lets you convert images from CMYK to RGB mode.
This works for any image, or for an in-progress file. If you have the Photoshop source file for the image that’s in CMYK, you can get excellent results when you convert it to RGB. If you don’t have the source file and are dealing with the final image, there may be some loss in color quality after the conversion.
CMYK To RGB Mode
Open the image or Photoshop file that is in CMYK mode in Photoshop. If you have a Photoshop file, it’s a good idea to edit it as much as you need to before you convert it from CMYK to RGB. This is because you might need to flatten the image in order to convert it and once the image has been flattened, you won’t be able to edit it any more.
With the file open, go to Image>Mode and select RGB Color.
You will see an on-screen prompt telling you to flatten the image if you haven’t flattened it already. You can flatten it or attempt to convert it without flattening the image and compare results. The action can be undone if you don’t like the results, and you can convert the image from CMYK to RGB again and choose to flatten the image before it’s converted.
You can likewise convert an image from RGB to CMYK. The process is the same except you have to select CMYK Color from the Mode sub-menu. With CMYK, you have to deal with color profiles. The default color profile may not give you the best results in which case you can change it and select a different one. Don’t guess what profile it is you should use. If you’re using CMYK, you likely intend to print whatever it is you’re making. Look up which profile is best for the print job you have on hand.