i understand the using of ProPhoto space. it's better to swim freely in the sea than strugling inside a small fish tank isn't it?
however here what im concerning is that, since the image is captures by the camera and assigned a profile that comes with it, those are all the possible gammut that that image could have. and because there's no way they'll fall outside of that gammut, what is the point of using a space larger than that?
I can't describe it any better than Bruce Fraser did.
Quote from Bruce Fraser on Adobe forums
“If you look at RGB matrix spaces (i.e., those defined by a white point, primaries, and gamma-defined tone curves) in a 3D lab plot like those offered by the ColorSync utility or Steve Upton's indispensable ColorThink, you'll see that they all reach their maximum saturation at a fairly high luminance level. The gamut narrows dramatically at lower luminances, tapering to a point at black.
Print spaces plotted the same way have a different shape, where maximum saturation is achieved at lower luminance levels. (In an RGB space, you make more saturation by adding light, on a printer you make more saturation by adding ink, so this makes sense.)
So an RGB matrix space that has a wide enough gamut at lower luminances to hold the printer gamut has to have extremely wide primaries that may not represent anything that's physically possible. Obviously, that leads to the space containing non-realizable colors. It's the trade-off you make when you want to create an RGB matrix space that contains all the realizable colors from your printer, and that's why ProPhoto is so large.
Then there's the question of clipping. It's not at all hard to capture colors that are outside Adobe RGB. Many of the dark greens and yellows that are prevalent in nature are outside Adobe RGB, and if you convert to Adobe RGB, or a smaller space, gradations of those colors get clipped to solid blobs. There's already been at least one such problem image posted on this forum. So the advantage of ProPhoto isn't about retaining all those out-of-gamut colors per se, it's about maintaining the distinctions between them, so that you can map them into printable space as gradations rather than blobs.”