If you are working with raw files then there will be a reduction in quality. But I don't think it will be anything that you will be able to actually see and be able to quantify. If you are creating this PDF to submit to a commercial printer I think you would want the images converted to sRGB. You would have to double check with your printing company, but I think that is what commercial printers require.
When printing a picture you don't need a wider color space like Adobe RGB or ProPhoto RGB? because paper cannot grab that quality form the wider color space?
In that case, for what reason do you need Adobe RGB or ProPhoto RGB color space?
If everything you print, you have to use sRGB, why Adobe RGB or ProPhoto RGB?
I ask because the PDF / X-4 allows a wider color space... so I am a bit confused?
Lightroom users ProPhoto RGB. That is the widest color space and affords you the most flexibility during the editing process. But most commercial printers expect your images in sRGB. After you have done all of your work in Lightroom or Photoshop or what ever, you reduce the color space to sRGB in preparation to send to the printer company. Lightroom does a pretty good job of handling that conversion. But before you do any conversion you need to consult the lab to verify what color space they require.
aha? then what is the purpose of Adobe RGB or ProPhoto RGB, if you always have to converto to sRGB to print the pictures?
if I will finally have to reduce quality, why do I need more quality in the edition process? and why then the PDF / X-4 which allow several color spaces?
Also, please, could you tell me how to convert from one color space to another color space in Lightroom?
I understand it that I use the wider color space during editing to enable me to see and use as much color as possible. I can soft proof in other color spaces to examine how the colors are affected, and adjust my editing accordingly to retain as much color depth as possible. Some printers and printing labs offer printing in other color spaces. I don't work with PDF files that much. So I can't really comment on the use of different color spaces. I "think" that PDF files are often organized and assembled for printing books and other types of documents on four-color presses. And I think that is where the different color spaces come into play. When you are dealing with digital images and typical printing then sRGB is pretty much the standard (as I understand it).
Lightroom displays in a modified ProPhoto color space. That cannot be changed. However, when you export copies you have the option to export in different color spaces. I know I haven't been real clear in my answers. But I've told you what I know and as well as I understand it.
Thanks a lot Jim. I guess that for printing a pictures book sRGB is enough and if we want a wider quality for a magazine, then, we have to move on to Indesign and use a wider color space exporting with PDF / X-4... However I think it would be a good idea Adobe add PDF / X-4 support to the PDF export feature of the pictures book in Lightroom.
I am posting it as a feature request in their forum.