1. The ProPhotoRGB. This color space is used by people who want to make sure they are retaining all the color information possible from their image captures. It’s one of those “you probably only want to use it if you already know why you want to use it” features, and is more appropriate for highest-end printers. The most important thing to know about using ProPhotoRGB as a working space is that to avoid paying for those extra colors with a greater risk of banding (visible steps between colors) in your images, you should work in 16 bit mode. ProPhotoRGB can represent many more colors than even AdobeRGB, including a relatively small slice of colors that high end inkjet printers can print that cannot be represented in AdobeRGB. It also includes a huge number of colors that digital cameras can capture but that can’t be displayed on any output device or printer, and even more colors that humans can see but that can’t be captured with any input device or displayed by any output device. What’s the use of all these colors if you can’t display or print them? First, you can be sure you haven’t thrown away any information that your camera captured until you absolutely must (when you output the file). For example, you could make a big hue / saturation change that moves previously unviewable and unprintable range of purplish reds into a range of deep blues that can be displayed. Or you might perform a sequence of editing steps that temporarily create extreme, unprintable colors and then later restore them to a printable range (say, by boosting overall color saturation and then cutting it back in specific areas). Having all those extra colors lets you do this without destroying color differences in the image. But ProPhotoRGB comes with a cost: To avoid banding you should work in 16 bit mode, which doubles file sizes, memory requirements, and operation times. Most Photoshop operations are available in 16 bit mode, but many of the creative filter operations are not.
AdobeRGB can represent more colors than sRGB — specifically including more saturated colors that inkjet printers can print. This profile is most appropriate for mid-range printers. So if you plan to print your images on an inkjet printer, you may wish to use AdobeRGB as your working space. You do this by setting your digital camera or scanner software to output AdobeRGB files, setting the output settings within Adobe Camera Raw to output AdobeRGB files, or, if creating documents from scratch in Photoshop, selecting Adobe RGB from the Color Profile pop-up in the advanced section of the New Document dialog.
sRGB can represent fewer colors than AdobeRGB, and inkjet printers can print many of those colors. This profile is best for all-in-one printers (that include a scanner and/or fax). So if you use sRGB, you will never see some of the more saturated colors that your digital camera or scanner can capture and your printer could print. But sRGB does include the vast majority of colors in the vast majority of images. Most monitors connected to the Internet are not color managed in any way, but they have device profiles that are close to sRGB, and many online print services require files that they print to have a working profile of sRGB. That means that for files to be posted on the internet or sent to such an online service, you should either use a working space of sRGB, or convert the file to sRGB before posting or sending it. You can convert a document to sRGB either by choosing Edit >Convert to Profile, and choosing sRGB as the Destination Space (leave other settings as they are), or by selecting the Convert To sRGB checkbox in the Save For Web And Devices dialog when saving a JPEG for the web.