This is driving me MAD: Colour management question
Discussion
4 replies
Posted by Rafael Rojas on November 28, 2009 at 2:15 PM
Hi all!. I have one of those "existential" questions about colour management...I need your help, because i am going mad with this...
I am working in lightroom with images. Lightroom uses as working space Prophoto RGB, which is the widest colour space available. When I export an image into photoshop, i export it with the colour space prophoto RGB embedded. Then, i open in PS the image (i have as working space in PS prophoto) and see the histogram, as in LR, appears ok. Then, as I will need to give away the image in RGB (getty submission for instance), I convert after all editiing the colour profile of the image from prophoto to adobe RGB. Now, as this colour space is narrower, I find out that the histogram gets clipped in one of the channels (blues for instance). The question I have is: When I do use the "convert to profile" in PS from prophoto to adobe RGB using a certain rendering intent (perceptual for instance) is not this conversion supposed to transform the colour space so that all colours that were into the gamut of prophoto space are in the gamut of the adobe RGB colour space? If this is what the colour profile conversion is about, why the hell do i find clipping after the conversion?
This question is the same as the following one, which was one concept I believed to have understood: When you softproof the output of a file by loading a custom output profile (for a certain printer + paper + ink), and you select "view-gamut warning", what you see as out of gamut (clipping) is in fact:
-The areas that are out of the gamut of the output profile, and that WILL BE CONVERTED (perceptual - relative...), or the areas that will REMAIN CLIPPED when the image is converted into that profile at the end of the day for printing? This question is in fact the same as the first one in my post.
What I understood is that when doing a profile conversion (perceptual, relative, etc) the algorithm did as needed to bring back the out of gamut values into the output profile, giving as a result an image whose histogram in the output colour space would remain unclipped.
The reason i am going through this is: I am using lightroom-develop to work my images (prophoto) but when I export them directly (LR-export) as Adobe RGB, I got all images with histograms clipped when you open them in photoshop (colour space RGB)...Normally clipping is small, but if you are submitting to Getty, they want histograms very clean...and they ask for RGB files. So, that means the only way i find to do that is leaving a lot of space in the LR develop histogram, so that when i send the file into RGB that gap is able to absorb the fact RGB colour space is narrower than the prophoto. But again, I thought till now that when I was doing from LR "export as RGB" , LR was "converting" from one colour space to the other, making sure all out of gamut colours would be "kept" back into the range of the output colour space (and if so, the histogram should look nice, without clipping).
Do I explain myself or this is a total mess?? Geez...
THANKS IN ADVANCE !!!
Posted by Kelly Rowe on November 28, 2009 at 3:01 PM
A couple of comments. First, does you camera record in prophoto color space? Our allow for sRGB and Adobe 1998 RGB. Any colors Lightroom processing introduces that are out of these gamuts are artificial, never really there. Ant time you move from a larger color space to a smaller one you will get clipping. How the clipping occurs depends on rendering intent. Relative intent stacks all out of gamut colors in the first in gamut location with complete disregard for the color relationships between the out of gamut colors. Perceptual intent preserves that relationship and does not stack every out of gamut color on the edge of the smaller gamut. Until displays and printers catch up with the theoretical, I would recommed using your capture color space throughout your workflow.
Posted by Rafael Rojas on November 28, 2009 at 4:15 PM
I get the point...But that would mean we should never use lightroom to develop our images? As this software works in Prophoto colour space, that means that if you "fix" the histogram doing corrections in lightroom till it just look right, it will always be clipped in some color channel when exporting the file in RGB. This is what is happening to me now...For printing and so on, I have never found any problem. But now that I want to provide files in RGB colour space whose histogram looks nice and proper in all colour channels (Getty will take a look with a magnifying glass), i find myself needing to start all over again, as all develop corrections made in lightroom were done according to the histogram displayed in that software (which shows everything according to a colour space wider than AdobeRGB, that is, Prophoto RGB).
Posted by David Bostedo on November 28, 2009 at 4:25 PM
Kelly - Your camera can probably record a larger space than Adobe RGB, but those settings only apply to JPGs. So Lightroom uses the largest space possible to make sure it can encompass everything in the RAW data for just about any camera. It's true that as you process the image, you might "create" colors that your camera couldn't have captured. That's the downside of working in a large space.
Rafael - Perceptual intent should be trying to maintain the relationship between colors to minimize clipping. It may cause some desaturation across the board as it tries to squeeze the large Prophoto space into sRGB. This assumes that you have colors that lie far outside of sRGB of course. I have seen cases at times where the color spaces you're using don't define the conversions for perceptual properly, and it looks identical to relative colorimetric (i.e. still clips). Here's an article on that.
Plus, there's nothing that says having the colors go to the edge of the histogram is "correct". If you want to convert from Prophoto to sRGB, you're going to do quite a large transformation. Minimizing colors at the edges, that don't exist in sRGB, will minimize how things change when you convert. I wouldn't really use the histogram to guide my editing and think there's any "right" histogram. Any image should look how you want it to regardless of the histogram.
Posted by Rafael Rojas on November 28, 2009 at 5:14 PM
I get the point...But that would mean we should never use lightroom to develop our images? As this software works in Prophoto colour space, that means that if you "fix" the histogram doing corrections in lightroom till it just look right, it will always be clipped in some color channel when exporting the file in RGB. This is what is happening to me now...For printing and so on, I have never found any problem. But now that I want to provide files in RGB colour space whose histogram looks nice and proper in all colour channels (Getty will take a look with a magnifying glass), i find myself needing to start all over again, as all develop corrections made in lightroom were done according to the histogram displayed in that software (which shows everything according to a colour space wider than AdobeRGB, that is, Prophoto RGB).
Discussion
4 repliesI am working in lightroom with images. Lightroom uses as working space Prophoto RGB, which is the widest colour space available. When I export an image into photoshop, i export it with the colour space prophoto RGB embedded. Then, i open in PS the image (i have as working space in PS prophoto) and see the histogram, as in LR, appears ok. Then, as I will need to give away the image in RGB (getty submission for instance), I convert after all editiing the colour profile of the image from prophoto to adobe RGB. Now, as this colour space is narrower, I find out that the histogram gets clipped in one of the channels (blues for instance). The question I have is: When I do use the "convert to profile" in PS from prophoto to adobe RGB using a certain rendering intent (perceptual for instance) is not this conversion supposed to transform the colour space so that all colours that were into the gamut of prophoto space are in the gamut of the adobe RGB colour space? If this is what the colour profile conversion is about, why the hell do i find clipping after the conversion?
This question is the same as the following one, which was one concept I believed to have understood: When you softproof the output of a file by loading a custom output profile (for a certain printer + paper + ink), and you select "view-gamut warning", what you see as out of gamut (clipping) is in fact:
-The areas that are out of the gamut of the output profile, and that WILL BE CONVERTED (perceptual - relative...), or the areas that will REMAIN CLIPPED when the image is converted into that profile at the end of the day for printing? This question is in fact the same as the first one in my post.
What I understood is that when doing a profile conversion (perceptual, relative, etc) the algorithm did as needed to bring back the out of gamut values into the output profile, giving as a result an image whose histogram in the output colour space would remain unclipped.
The reason i am going through this is: I am using lightroom-develop to work my images (prophoto) but when I export them directly (LR-export) as Adobe RGB, I got all images with histograms clipped when you open them in photoshop (colour space RGB)...Normally clipping is small, but if you are submitting to Getty, they want histograms very clean...and they ask for RGB files. So, that means the only way i find to do that is leaving a lot of space in the LR develop histogram, so that when i send the file into RGB that gap is able to absorb the fact RGB colour space is narrower than the prophoto. But again, I thought till now that when I was doing from LR "export as RGB" , LR was "converting" from one colour space to the other, making sure all out of gamut colours would be "kept" back into the range of the output colour space (and if so, the histogram should look nice, without clipping).
Do I explain myself or this is a total mess?? Geez...
THANKS IN ADVANCE !!!
Rafael - Perceptual intent should be trying to maintain the relationship between colors to minimize clipping. It may cause some desaturation across the board as it tries to squeeze the large Prophoto space into sRGB. This assumes that you have colors that lie far outside of sRGB of course. I have seen cases at times where the color spaces you're using don't define the conversions for perceptual properly, and it looks identical to relative colorimetric (i.e. still clips). Here's an article on that.
Plus, there's nothing that says having the colors go to the edge of the histogram is "correct". If you want to convert from Prophoto to sRGB, you're going to do quite a large transformation. Minimizing colors at the edges, that don't exist in sRGB, will minimize how things change when you convert. I wouldn't really use the histogram to guide my editing and think there's any "right" histogram. Any image should look how you want it to regardless of the histogram.