Are you referring to the embedded JPEG previews?
I always (maybe wrongly) assumed they were in the same colour space as what was set in the camera at the time. I never understood why Nikon insists on moving the underscore in the filename, depending on the selection of sRGB or AdobeRGB, and how it affects the rendition of the embedded preview.
Having said that, I have no basis in proof, so I'm just thinking out loud. I must stop doing that ;-)
Profile/color space can be anything - there is a DNG tag called "PreviewColorSpace" that allows for:
- 0 = Unknown
- 1 = Gray Gamma 2.2
- 2 = sRGB
- 3 = Adobe RGB
- 4 = ProPhoto RGB
Good practice would be to attach an ICC profile to the preview, but I don't think there's any requirement to do so.
Perfect. - thanks Sandy. So far my brief spot checks had revealed no icc-profile but perfect color match (all 2's: sRGB - that explains it). All such DNG previews were written by Lightroom, making me wonder if Lr always writes sRGB, despite DNG being spec'd for other options. Cheers, Rob.
Yammer P wrote:
I always (maybe wrongly) assumed they were in the same colour space as what was set in the camera at the time.
So far, there has been no apparent corrolation to original in-camera color space. (My NEFs were AdobeRGB, but after conversion to DNG, the initial & updated previews are sRGB).
I'd think that that LR would indeed always write sRGB previews; that's what I'd do as it certainly maximises compatibility.
Thanks again Sandy. I'm writing a preview reader - maybe I'll just detect what it should be and issue a warning if it's not sRGB, since that may be enough, and if people are being bombarded with warnings, they can request more proper handling... Cheers, Rob.