From: "John Bean"
wrote:
John Bean wrote:
Only later when the raw files are converted to RGB is a
colour space chosen, so there’s no "expansion" at all by using ProPhoto, just less clipping than would occur if using either of the two much smaller spaces.
Agreed, but if the color space provided by the RGB filters in the camera did not provide the colors to fill the chosen colorspace, then using that space or gamut is pointless.
But not harmful either. Someone suggested that ProPhoto
somehow is "worse" than Adobe RGB, and that’s simply not true.
Not to single out John, but I think beginners should be very careful about separating wheat from chaff in this particular thread.
The "expansion" of ProPhoto RGB can have serious consequences, particularly for 8 bit per channel images. ProPhoto RGB, as with any very wide gamut space, can result in unacceptable noise, and posterization of the image. In 16 or 32 bit per channel this is not the case, however not all of us will choose to work at that bit depth, particularly when no clear advantage to working in ProPhoto RGB has been demonstrated.
Because of it’s immense gamut, ProPhoto RGB also produces artifacts, in some situations, when converting to Lab. Try it yourself – create a white to blue gradient and convert it from ProPhoto RGB to Lab – see the black band at about the three quartertone? This occurs in 8 as well as 16 bit images.
Consider a camera that has blue and green filters, but no red filter.
No point. Lets consider reality instead, and the colour
gamut of any Bayer sensor doesn’t fit in either sRGB or
Adobe RGB.
I’m not so sure. Adobe RGB is actually quite large, for an RGB space, and it may well be sufficient for many of the sensors out there.
Less clipping occurs if you use ProPhoto RGB when converting raw images. If you’re unconvinced then a lot of expert
opinion says this is so. Perhaps you haven’t read Bruce
Fraser on this subject, to name just one.
Fraser is a great guy, and I have read his books, but why is it necessary to appeal to authority?
Seeing is believing. If ProPhoto RGB has a decisive advantage, it should be easy to come up with a photograph in which use of ProPhoto RGB results in a markedly better image – printout, screen, what have you, than the same image exported in Adobe RGB or sRGB.
Again, not to put John on the spot here, but in all seriousness, I’m genuinely interested. Does anyone have such an image? For example, a raw file where the ProPhotoRGB image contains detail or color that goes away when the same image is exported as Adobe RGB?
I suspect I will wait a long time before being presented with such an image, so I will say this: Given the great number of new ideas that are being tried right now, it’s a safe bet that many of them are simply wrong. Lack of an image demonstrating a particular principle is a good indication that that principle is not going to pan out, in the long run.
Until a photograph that demonstrates the superiority of ProPhoto RGB appears, I think those of us who work in Adobe RGB and sRGB may rest easily, whatever the "authorities" may say.
Indeed, even if one or two images do turn up, I believe it is the case that for the vast majority of photos, ProPhoto is overkill, and 16 bits per channel is overkill. Toolmaker that I am, I say this with respect for those who take excellent photographs, and who believe otherwise. —
Mike Russell
www.curvemeister.com