Google| Subject | Re: Any Minolta/Sony users using UFRaw and GIMP? |
| From | nospam |
| Date | 04/18/2014 04:31 (04/17/2014 22:31) |
| Message-ID | <170420142231041247%nospam@nospam.invalid> |
| Client | |
| Newsgroups | rec.photo.digital |
| Follows | Eric Stevens |
| Followups | Eric Stevens (2h & 32m) > nospam PeterN (13h & 14m) > nospam Eric Stevens (3d, 2h & 17m) > nospam |
In article <9k21l9hvc6r69oom5034437cdeefimsch0@4ax.com>, Eric Stevens <eric.stevens@sum.co.nz>wrote:
it doesn't.Eric StevensnospamEric StevensEric Stevensnospam
But doesn't the Adobe color engine work in Lab anyway?
internally, but that's not the same as making a conversion of the image twice.
What are the two conversions?
rgb->lab->rgb
But isn't that exactly what the colour engine has to do?
It gets fed an RGB file from outside, then converts it to Lab for it's own processing and then converts it back to RGB for output to the monitor. It may also convert it to CMYK for output to a printer or saving it to a disc. http://www.eizo.com/global/library/management/cms/02e.jpg is the kind of diagram commonly used to explain this.
from "color management for photographers: hands on techniques for photoshop users" by andrew rodney, page 53:
Editing in LAB: I have nothing against the LAB color model. However, there are a group of people who feel that editing in LAB is the only way to accomplish specific corrections, making it sound like a macho editing space. It is true, there are a few correction techniques that rely on a document being in LAB color space. The question becomes whether its worth taking the time or worse, producing image degradation to convert from a working space to LAB and back. Every time a conversion to LAB is produced, the rounding errors and severe gamut mismatch between the two spaces can account for data loss, known as quantization errors. The amount of data loss depends on the original gamut size and gamma of the working space.
...
Some users are under the impression that Photoshop does all its conversions to and from LAB, converting on-the-fly. this is untrue as it would greatly slow down performance. Instead, Photoshop uses LAB as a reference when conducting many operations. Photoshop is not actually converting pixel data between color spaces unless you, the user, actually ask for this. None of these issues should be interpreted as implying that a conversion from working space to LAB is bad. Just be aware of the issues involved with this kind of conversion and whenever possible, try to use similar techniques that can be conducted in the RGB working space.
04/05/2014-
