Noted photographer Stephen Johnson writes in On Digital Photography that "Color management could also be known as color confusion, marketing hyperbole, or the black hole." One of the most potentially confusing aspects of color management is color spaces. This is a vast topic but, essentially, color spaces are mathematical representations of the way that we perceive colors. Different colorspaces work better for different purposes. They also stir strong opinions--viz. Dan Margulis' Photoshop LAB Color: The Canyon Conundrum and Other Adventures in the Most Powerful Colorspace.
The good news is that the typical photographer doesn't need to worry too much about all this. Most of the time. However, every now and then color space issues jump out and bite you.
With that by way of introduction, here's today's tip for using Adobe Lightroom, Adobe's cataloging and non-destructive image editing program.
For a while, I had a sort of vague impression that the photos I was putting up on Flickr maybe seemed a bit darker and lacked a bit of "pop" relative to those same photos when I was editing them within Lightroom. Finally, after running across one photo where the difference was particularly clear, I decided to look into the issue a bit more carefully.
It turned out that, not only was the photo darker and cooler (i.e. more toward blue) when looking at it on Flickr using Firefox, but the same JPEG was also darker and cooler when I looked at it on my PC using IrfanView, an image viewing program. Furthermore, if I then re-imported that JPEG back into Lightroom and looked at it from within Lightroom, it was lighter and warmer again. Thus the problem seemed to relate to how Lightroom was displaying the picture rather than problems related to converting it from its original as-shot RAW format to JPEG.
It was a color space issue.
Adobe Lightroom uses the ProPhoto RGB color space internally. It can export to either ProPhoto RGB, Adobe RGB (1998), or sRGB. Essentially, these are different standards for defining what human-perceived shades of color correspond to which numeric values of (R)ed, (G)reen, and (B)lue. Most monitors and other output devices are calibrated for sRGB. However, ProPhoto RGB and Adobe RGB are "larger" color spaces--that is, they're able to represent a larger proportion of the colors that a person can see. (See this article on The Luminous Landscape for a more detailed explanation.)
The problem with using a color space that's different from your monitor's is that something has to map one to the other. As Colin Southern notes in this photo.net post:
If you capture an image and save it in Adobe RGB format, and then display it or print it on a device that's expecting sRGB, then the image won't display correctly--in general it will be darker with more subdued colors.
To explain why it looks darker when Adobe RGB has more colours...think of a single red pixel--that pixel under sRGB might have a value of 200 (out of 254)--but because Adobe RGB has to allow for more colours it has to be more conservative in its numbering (because 254 is still the limit)--so in Adobe RGB that same red pixel--at the same level of brightness might only be given a number of 175. Now when you display that (Adobe RGB) pixel in a program that thinks it's a sRGB pixel all it sees is a pixel that's 175 (not 200)--so it displays it dimmer.
(I've replaced aRGB with Adobe RGB in the above quotation to avoid confusion with Apple RGB, a close relative of sRGB that's no longer widely used.)
That was my problem. I was exporting to JPEGs with an Adobe RGB color space. Lightroom (like Photoshop and other higher-end imaging programs) understand how to properly display images using that color space on an sRGB monitor. However, neither Firefox nor IrfanView do.
Moral of the story? Although Apple's Safari and the Firefox 3 beta can display non-sRGB color spaces correctly, Microsoft's Internet Explorer and Firefox 2.x don't. Nor do most basic file viewers. Therefore, for most purposes--and certainly for Web display--it's best to use JPEGs with an sRGB color space or the results probably won't be what you expect.