RGB JPEG is the default image format for photographs from digital cameras, cell phones and other mobile devices. RGB stands for red, green and blue. Screen images on computers, TVs, phones and cameras are comprised of these three colors in varying percentages to make up the full-color image or photograph on their display. If you intend to use a JPEG in a printed publication, such as a magazine, brochure or leaflet, you must convert the image to CMYK to be compatible with a commercial printing press. A commercial printer separates artwork into four color plates; cyan, magenta, yellow and black, or CMYK. The 'K' stands for 'keyline' and represents the black plate. Each separated color is printed over the next until a composite full-color document is achieved.
Open Adobe Photoshop. Go to "File" in the menu bar at the top of the screen and click on "Open".
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Browse the folders on your computer and select the required JPEG file.
Click on the "Image" tab in the menu and scroll down to "Mode" to produce a drop-down sub-menu.
Roll the cursor over the drop-down sub-menu and select "CMYK".
Go to "File" in the menu bar and click on "Save As". Choose a name for the new file and click "Save" to store the CMYK JPEG in a folder of your choice.