MarkBarbieri
Semi-retired
- Joined
- Aug 20, 2006
- Messages
- 6,171
DueyDooDah recently started a poll thread asking whether people used sRGB or Adobe RGB. I'm guessing that the subject has a lot of people scratching their heads, so I'm going to take a shot at explaining it.
When your camera takes a picture, it measures the amount of red light, blue light, and green light for each pixel. It assigns each of those colors a value from 0 to 255. (Some cameras actually count from 0 to 4095, but let's just assume that they all use 0 to 255 for now). A 0 means that there is none of that color and 255 means that there is as much of that color as the camera can record.
0 for all three means that the pixel is black and 255 for all three means that the pixel is white. Aside from that, there really aren't any rules. A pixel with a value of 200 for red, 0 for green, and 0 for blue is definitely a shade of red, but exactly which shade of exactly which red isn't defined by a standard.
That's where colorspaces come into play. A colorspace is just a set of definitions for what colors the numbers mean. In sRGB, 200 for red, 0 for blue, and 0 for green refers to a precise shade of red that is universally agreed upon. In AdobeRGB, it also refers to a particular shade of red, but that shade is different than sRGB. A colorspace is just a standard for translating color numbers into actual colors.
There are lots of different colorspaces. The three that I see most commonly with digital photography are sRGB, AdobeRGB, and ProPhoto RGB. The RGB part stands for "Red", "Green", and "Blue". There are other colorspaces that are CMYK (Cyan, Magenta, Yellow, and Black). There are even others that aren't defined by mixtures of absolute colors, like CIELAB, but we'll ignore those.
So why do we need more than one colorspace and why does it matter which one I use? Each colorspace describes a different possible set of colors. Your camera is capable of capturing some colors, but not all. Your monitor is capable of displaying some colors, but not all. Your printer is capable of printing some colors, but not all. Each has a native colorspace that it is capable of reproducing. If you use the wrong colorspace, your might be asking a device to reproduce a color that it cannot, which leads to problems.
The sRGB colorspace is a relatively small colorspace. It's similar to the capabilities of most monitors. Most cameras are capable of capturing lots of colors that don't fit into the sRGB colorspace. There is just no set of numbers in the sRGB colorspace that match those colors. When your camera (or your RAW conversion software) converts your photo into sRGB, it does some tricks to make everything fit. In some cases, it might just clip the colors. Perhaps anything "yellower" than a certain "yellow" just gets set to the most yellow color in sRGB. Other converters do tricks like reduce the amount of yellowness of everything near the limit so that everything can be fit inside the limit.
AdobeRGB is a much wider colorspace. Things that would be outside of the range of colors described by sRGB might still fit into the range of AdobeRGB. If you work with AdobeRGB, you will have fewer problems with colors being clipped and you'll be able to work with a wider range of colors.
Keep in mind, however, that your photo has the same number of different possible photos (0-255 for red, 0-255 for blue, and 0-255 for green) regardless of whether you use a small colorspace like sRGB or a wider colorspace like AdobeRGB. The difference is that each change in numbers makes for a smaller change in colors in sRGB than it does in AdobeRGB. In other words, there is less red added when you go from 200 to 201 as the value for red in sRGB and more red added for the same number change in AdobeRGB. Anytime you increase the size of the colorspace but keep the same range of values, the difference in values has to be bigger.
Even AdobeRGB doesn't cover the entire range of most digital cameras. ProPhoto RGB was created for that purpose. It doesn't always cover every possible color either, but it's wider than AdobeRGB and is less likely to lead to clipping. Here is an illustration from a Luminous-Landscape article on ProPhoto RGB, which actually comes from A Color Management Workflow on Adobe's web site.
You can get a sense for the relative ranges of colors each of the colorspaces mentioned can show.
The really nice thing about using a colorspace is that you get consistent color. If your RAW converter properly translates your camera's sensor values to accurate colors in the colorspace, you can have consistent color between what you saw, what your camera recorded, what displays on your monitor, and what appears on your printer. It can even be consistent when other people look at it. The trick is that everyone must be using devices that understand the colorspace being used. Each device is still limited by its own colorspace (the range of colors it is capable of displaying or printing), but if it understands the colorspace of the photo, it can do it's best to make it look consistent.
A big problem in the digital photo world is that so many applications don't know anything about colorspaces. Microsoft is notorious for being colorspace clueless. I don't know if even the latest versions of Internet Explorer are colorspace aware. As it happens, sRGB is a reasonably good approximation for how most computers running Windows display colors anyway. For this reason, almost all pictures published on the web use sRGB.
If you create a JPG with the AdobeRGB colorspace or the ProPhoto RGB colorspace, it's probably going to look bad to a lot of other people. It might look great in Safari, Photoshop, or other colorspace aware applications. When someone pulls it up in IE6 or some other colorspace ignorant application, it will look much more muted than it should. For this reason, even if you work in a different colorspace, it is always best to convert JPGs that you intend to post for a general audience to sRGB.
So the main benefits to working with a colorspace is that it allows you to share a picture between different applications and display or printing devices and know that the colors won't change between them. Working with a wider colorspace like AdobeRGB or ProPhotoRGB will allow you to have more vibrant colors in your picture. You might not notice the difference on your monitor (which probably has to translate everything to a more restricted colorspace anyway), but you should see a difference when you print.
Does that help?
When your camera takes a picture, it measures the amount of red light, blue light, and green light for each pixel. It assigns each of those colors a value from 0 to 255. (Some cameras actually count from 0 to 4095, but let's just assume that they all use 0 to 255 for now). A 0 means that there is none of that color and 255 means that there is as much of that color as the camera can record.
0 for all three means that the pixel is black and 255 for all three means that the pixel is white. Aside from that, there really aren't any rules. A pixel with a value of 200 for red, 0 for green, and 0 for blue is definitely a shade of red, but exactly which shade of exactly which red isn't defined by a standard.
That's where colorspaces come into play. A colorspace is just a set of definitions for what colors the numbers mean. In sRGB, 200 for red, 0 for blue, and 0 for green refers to a precise shade of red that is universally agreed upon. In AdobeRGB, it also refers to a particular shade of red, but that shade is different than sRGB. A colorspace is just a standard for translating color numbers into actual colors.
There are lots of different colorspaces. The three that I see most commonly with digital photography are sRGB, AdobeRGB, and ProPhoto RGB. The RGB part stands for "Red", "Green", and "Blue". There are other colorspaces that are CMYK (Cyan, Magenta, Yellow, and Black). There are even others that aren't defined by mixtures of absolute colors, like CIELAB, but we'll ignore those.
So why do we need more than one colorspace and why does it matter which one I use? Each colorspace describes a different possible set of colors. Your camera is capable of capturing some colors, but not all. Your monitor is capable of displaying some colors, but not all. Your printer is capable of printing some colors, but not all. Each has a native colorspace that it is capable of reproducing. If you use the wrong colorspace, your might be asking a device to reproduce a color that it cannot, which leads to problems.
The sRGB colorspace is a relatively small colorspace. It's similar to the capabilities of most monitors. Most cameras are capable of capturing lots of colors that don't fit into the sRGB colorspace. There is just no set of numbers in the sRGB colorspace that match those colors. When your camera (or your RAW conversion software) converts your photo into sRGB, it does some tricks to make everything fit. In some cases, it might just clip the colors. Perhaps anything "yellower" than a certain "yellow" just gets set to the most yellow color in sRGB. Other converters do tricks like reduce the amount of yellowness of everything near the limit so that everything can be fit inside the limit.
AdobeRGB is a much wider colorspace. Things that would be outside of the range of colors described by sRGB might still fit into the range of AdobeRGB. If you work with AdobeRGB, you will have fewer problems with colors being clipped and you'll be able to work with a wider range of colors.
Keep in mind, however, that your photo has the same number of different possible photos (0-255 for red, 0-255 for blue, and 0-255 for green) regardless of whether you use a small colorspace like sRGB or a wider colorspace like AdobeRGB. The difference is that each change in numbers makes for a smaller change in colors in sRGB than it does in AdobeRGB. In other words, there is less red added when you go from 200 to 201 as the value for red in sRGB and more red added for the same number change in AdobeRGB. Anytime you increase the size of the colorspace but keep the same range of values, the difference in values has to be bigger.
Even AdobeRGB doesn't cover the entire range of most digital cameras. ProPhoto RGB was created for that purpose. It doesn't always cover every possible color either, but it's wider than AdobeRGB and is less likely to lead to clipping. Here is an illustration from a Luminous-Landscape article on ProPhoto RGB, which actually comes from A Color Management Workflow on Adobe's web site.
You can get a sense for the relative ranges of colors each of the colorspaces mentioned can show.
The really nice thing about using a colorspace is that you get consistent color. If your RAW converter properly translates your camera's sensor values to accurate colors in the colorspace, you can have consistent color between what you saw, what your camera recorded, what displays on your monitor, and what appears on your printer. It can even be consistent when other people look at it. The trick is that everyone must be using devices that understand the colorspace being used. Each device is still limited by its own colorspace (the range of colors it is capable of displaying or printing), but if it understands the colorspace of the photo, it can do it's best to make it look consistent.
A big problem in the digital photo world is that so many applications don't know anything about colorspaces. Microsoft is notorious for being colorspace clueless. I don't know if even the latest versions of Internet Explorer are colorspace aware. As it happens, sRGB is a reasonably good approximation for how most computers running Windows display colors anyway. For this reason, almost all pictures published on the web use sRGB.
If you create a JPG with the AdobeRGB colorspace or the ProPhoto RGB colorspace, it's probably going to look bad to a lot of other people. It might look great in Safari, Photoshop, or other colorspace aware applications. When someone pulls it up in IE6 or some other colorspace ignorant application, it will look much more muted than it should. For this reason, even if you work in a different colorspace, it is always best to convert JPGs that you intend to post for a general audience to sRGB.
So the main benefits to working with a colorspace is that it allows you to share a picture between different applications and display or printing devices and know that the colors won't change between them. Working with a wider colorspace like AdobeRGB or ProPhotoRGB will allow you to have more vibrant colors in your picture. You might not notice the difference on your monitor (which probably has to translate everything to a more restricted colorspace anyway), but you should see a difference when you print.
Does that help?
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