Timeline for Is conversion from one colour profile to another clearly defined
Current License: CC BY-SA 3.0
11 events
| when toggle format | what | by | license | comment | |
|---|---|---|---|---|---|
| Nov 18, 2015 at 12:42 | comment | added | Paul Taylor | Okay so Im now using Lightroom6 which lets me soft proof to a CMYK profile and I can see that neither sRGB and CMYK can accurately map many pixels for certain images, the ProPhoto profile does. But Lightoom doesnt allow me to specify a CMYK profile when exporting even when I use TIFF so Im thinking export with ProPhoto rather than sRGB so no mapping problem at that point, so we only get mapping adjustments when printer converts to FOGRA but then we have no choice over whether they do perpetual or relative conversion, I cant see how to get round that. | |
| Nov 18, 2015 at 0:19 | comment | added | Itai | Unless you export a TIFF, you won't be able to have a CMYK file. It will be RGB with a color-space attached to describe what these values mean. It will be the responsibility of the printer software to use the RGB value and profile together to perform the conversion. If you want to RGB values to be of a specific profile (most commonly sRGB) then some application can output a JPEG like that without color-profile, so it is the responsibility of the application to interpret it correctly. | |
| Nov 17, 2015 at 21:39 | comment | added | Paul Taylor | I might be wrong but I think youre saying that Lightroom always has the raw image and can therefore ensure we dont lose information if we have to do multiple mappings ? But that is all well and good but at some point I need to export an image that can be used and printed outside of Lightroom, so Im expecting the exported image to use the profile required for printing and therefore wont it now have different pixel values because different models would have different rgb values mapping to the same LAB value( or equiv CMYK value if a CMYK based profile for printing) | |
| Nov 17, 2015 at 21:23 | comment | added | Itai | OK, let me simplify. When embedding the profile, one does not need to transform pixels, only the viewer does. Without a profile, the only choice is doing the transformation to a known common profile which is usually sRGB. Having the viewer do the transform allows to compose mappings and reduce artifacts in the process since another mapping might be needed to get pixels in the display or print color-space. | |
| Nov 17, 2015 at 20:56 | comment | added | Paul Taylor | sorry I dont understand what you are saying | |
| Nov 17, 2015 at 19:28 | comment | added | Itai | Not 100% sure about LR but IIRC, it just converts without asking, so what choice it does is fixed. In theory you can and there are plenty of mappings possible. If you embed the color-profile, then it does not have to change values, otherwise, it has no choice but to produce pixels of certain values according to the mapping it uses. | |
| Nov 17, 2015 at 18:57 | vote | accept | Paul Taylor | ||
| Nov 17, 2015 at 18:29 | comment | added | Paul Taylor | But I dont see you can use perceptual/relative except when soft proofing. Because for example if I export a image as a jpeg in Lightroom I can specify the embedded profile but I don't specify how it is done, or does it literally just change the profile without actually converting the rgb vales from rgb -> lab > newrgb when I pick this option. To put it another way can I properly convert image from one profile to another at export stage or it only to be used to correctly specified the right profile in case it is currently set wrong. | |
| Nov 17, 2015 at 18:27 | comment | added | Paul Taylor | Ah useful link but I think this is the one I needed color-management-guide.com/convert-to-profile-an-image.html I thought when you changed colour profile the RGB values didn't change but just how they mapped to LAB changed. Whereas actaully if you have the right profile to start with and then change to another profile it goes RGB - > LAB and then LAB -> new RGB and the problems arise when original RGB maps to a particular LAB value, and that LAB value isn't mapped to by RGB in the colour space, which is where they have some leeway. | |
| Nov 17, 2015 at 18:06 | comment | added | Paul Taylor | Ive fixed the question regarding colour profiles and spaces | |
| Nov 17, 2015 at 17:32 | history | answered | Itai | CC BY-SA 3.0 |