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Color Space (sRGB, Adobe RGB, ProPhoto RGB)

As color spaces go, they all share the same characteristics. They all have three channels of data, one for red, one for green, and one for blue. In 8 bit mode (255 possible colors in each channel) there are roughly 16.7 million colors available. 16 bit images have the capacity to display approximately 281 trillion colors.
Color Gamut

SRGB is the smallest of the photographers color spaces. It is about 20 percent smaller than Adobe RGB and half the size of ProPhoto RGB. It is used in 8 bit mode. So why use it? Well, most common programs and web browsers are not color management aware, and hence they display all colors as if they were sRGB.

Adobe RGB is the bigger brother of sRGB. It has the capacity to display the more saturated colors located outside the sRGB color space.

RGB comparison 
Adobe RGB does not use more colors, they are just further apart.

If you were to take an Adobe RGB image and display it as if it were an sRGB, it would look unsaturated and washed out. That is because all the colors beyond the orange line in the Adobe RGB color space would be discarded. You would lose all the highly saturated colors resulting in the washed out image.

The fact that Adobe RGB uses the same amount of colors to represent a bigger color space can lead to problems when editing due to the larger gaps in between colors. These problems can show up as banding and other artifacts. The difference between 210 and 211 in Adobe RGB is much more visible than in sRGB. The solution to this problem is to work in the 16 bit color depth.

In 16 bit depth, there are more than 281 trillion total colors available. This is because there are now 65536 colors available in each channel instead of the 255 in 8 bit depth. These extra colors are more than enough to fill in these "gaps".

Adobe RGB 16 bit 
Now there are more colors available so they fill in the gap.

16 bit mode does not allow more saturated colors than 8 bit mode, but rather more colors in between the existing 8 bit colors. It is actually better to do all you image editing in 16 bit mode especially when working with a large gamut color space.

Shooting jpegs forces you to decide what color space to set in your camera. If all your images are going to the web, sRGB would make sense. If you do any printing and/or editing of you images, you will be better off using Adobe RGB. However, if you decide to shoot RAW, you do not have to make a choice in the camera. The RAW file gets converted to whatever color space you decide when you import it into an image editing program. Also note that most digital SLR sensors can capture colors that are outside the Adobe RGB color space. This leads us to ProPhoto RGB.

For the time being, you have to shoot raw images to be able to take advantage of ProPhoto RGB. That is until digital cameras allow us to select it in camera.

ProPhoto RGB is about 50 percent bigger than Adobe RGB. Some Epson printers are capable of printing colors outside the Adobe RGB color space, namely in the orange and yellows. ProPhoto RGB covers all of these colors, but also some that are not even visible, let alone printable. In fact, the color space is so big that even in 16 bit mode, you risk banding and artifacts due to the "gaps" between the colors. Generally, you only want to use ProPhoto if you see clipping in the Adobe RGB color space.

Using Adobe Camera RAW to open your raw files, allows you to select which color space you want to open your image in.
RAW workflow

Here you can choose Adobe RGB, ProPhoto RGB, sRGB, and Color Match RGB. You can also select your bit depth, size, and resolution. Here you need to make a choice. If the image is going straight to the web with no editing, then open it in sRGB. If you plan on editing, use Adobe RGB unless you see color clipping in the histogram. In such a case, open the file using the ProPhoto color space.

Once you have your file open in ProPhoto RGB you have to be careful. The huge size of the color space and the size of the gaps between the colors means that you risk banding and other rounding errors if you are not careful. Do not even think of using ProPhoto RGB in 8 bit mode. The results are disastrous.
This shows what happens when you edit a large gamut image in a low bit depth. The gaps in the histogram indicate abrupt tonal or color transitions. This is due to the lack of available colors that would normally be able to represent these missing colors in 16 bit mode.

Generally what I do is immediately after opening the image using the ProPhoto RGB color space, I covert it to Adobe RGB while keeping it in 16 bit mode. This way you are able to do a lot more editing without the risk of errors. Also keep in mind that you want to convert to Adobe RGB using the Perceptual rendering intent. Doing this will compress the color gamut (range) rather than clipping it.

So what does all this mean? Well, if you want the absolute best out of your images, shoot RAW and process as you need to. Until a 32-bit mode becomes available, stick with Adobe RGB and 16 bit mode for your editing to maximize your image potential and avoid problems.


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