Converting profile.

Hi

I have a question about correctly converting an image to a different colour space for use with different outputs. Is it possible to maintain the image's appearance when converting an image that has already been adjusted and finalised to a particular colour space? Or, do I need to put the file through my workflow for each colour space based on it's intended output?

To be clearer, I know about the convert to profile function in PS. What's confusing me is that when I do this the colour values remain the same. As an example, if I create a new canvas with an SRGB profile then fill that canvas with the colour R 0, G 0, B255, if I convert this to Adobe RGB, these numeric values remain the same but the Adobe equivalent of this colour will be very different. I'm assuming, that if I had the SRGB version of this file on a website and a print from the Adobe RGB version (printed from a printer that used an Adobe RGB profile), the two would not look the same.

Thanks.

Hi

I have a question about correctly converting an image to a different colour space for use with different outputs. Is it possible to maintain the image's appearance when converting an image that has already been adjusted and finalised to a particular colour space? .

Depends on the source color space and it's color gamut, and the destination color gamut.

To be clearer, I know about the convert to profile function in PS. What's confusing me is that when I do this the colour values remain the same. As an example, if I create a new canvas with an SRGB profile then fill that canvas with the colour R 0, G 0, B255, if I convert this to Adobe RGB, these numeric values remain the same but the Adobe equivalent of this colour will be very different. I'm assuming, that if I had the SRGB version of this file on a website and a print from the Adobe RGB version (printed from a printer that used an Adobe RGB profile), the two would not look the same.

The numbers may be the same but the scale of the number and thus the color, is not.

If I tell you I weight 170, you don't have a scale. Could be pounds, or Kilo's.

R 0, G 0, B255 in sRGB is a different scale (same triplets) than R 0, G 0, B255 in Adobe RGB (1998). Just as 170 is the same number, but a scale of the numbers is necessary.

Examine both R 0, G 0, B255 or any triplet in an RGB color space as Lab; you'll see a different value when the identical triplets (like the 170) is examined.

You have two choices in Photoshop: Convert, or Assign.

If you Convert, the image data (numbers) are changed so that the colors agree with the new color space. In general, you won't see a noticeable change (gamut limitations excepted), but the change may be lossy.

If you Assign, the new color space is embedded to replace the previous assignment. The colors will change accordingly. The main reason for assigning a new color space is to embed it where none existed before (common on web downloads). Try different color spaces until you find one which doesn't noticeably change the image. The change is lossless, since no image data is changed, only the colors displayed for those numbers.

I appreciate your replies, I think my question may not have been completely clear.

Digitaldog, you may have misunderstood my attempt to clarify on what issue I'm having, as you've repeated my explanation back to me. I do understand that these are entirely different scales, I understand that the R0, G0, B255 value in Adobe RGB sits deeper into the colour spectrum than it does with SRGB, which is why Abode images look overly saturated if I 'convert to profile'.

Ed_Ingold, assigning produces the same result, colour values remain the same between colour profiles, so the outputs will look different unless they adjusted from the RAW file.

My question is, whether there is a way to perform, what might be described as a fixed point conversion, as if SRGB were simply an overlay over the coordinates within Adobe RGB? Basically, I 'd like to save time by not having to do all my adjustments multiple times for different colour spaces, and I don't know if that's even possible.

I'll try and explain myself in another way, hopefully I won't make things worse.

If you have two scales, both divided into 10 units where one scale only covers five units of the other scale. If these scales are SRGB and ARGB, is there a way to convert SRGB so the value of it's units are halved and it's 10th unit is given a value of 5, post conversion?

Ed_Ingold, assigning produces the same result, colour values remain the same between colour profiles, so the outputs will look different unless they adjusted from the RAW file.

I presume you haven't actually tried assigning a color space. The changes are not permanent until you save the image, so you can experiment freely.

Converting the color space has no visible effect on color, including previous adjustments, unless you exceed the gamut (which is rare).

In either case, what you see after the change is the output.

File you load into Photoshop will look mostly the same, regardless of their color space, because Photoshop recognizes the embedded space and adjusts the color interpretation accordingly.

I use these features when applying a custom profile (e.g., derived from an image of a standard color chart). I first "assign" the custom profile, which synchronizes the image with the color chart. I then "convert" the custom profile to a standard profile, like AdobeRGB or sRGB so others can use the file more easily.

Digitaldog, you may have misunderstood my attempt to clarify on what issue I'm having, as you've repeated my explanation back to me. I do understand that these are entirely different scales, I understand that the R0, G0, B255 value in Adobe RGB sits deeper into the colour spectrum than it does with SRGB, which is why Abode images look overly saturated if I 'convert to profile'.

Deeper color? Adobe RGB (1998) has a wider gamut than sRGB; it has a wider range of colors.

Adobe RGB (1998) shouldn't look overly saturated if properly color managed.

I think you should start here then ask questions:

Everything you thought you wanted to know about color gamut

A pretty exhaustive 37 minute video examining the color gamut of RGB working spaces, images and output color spaces. All plotted in 2D and 3D to illustrate color gamut.

High resolution: http://digitaldog.net/files/ColorGamut.mov

Low Res (YouTube):

Hi Andrew, Ed

the video was incredibly helpful. I feel a little silly, in my original post my question was based on an experiment similar to your three pixel demonstration but I stupidly only did it with the blue value and only switching between SRGB and Adobe RGB, not realising that their most saturated blue has the same value. That's why I was insisting that the values weren't changing, hopefully I didn't come across as being unreceptive to what you were describing. Once I introduced the other two colours and Prophoto RGB the values changed and what both you and Ed were saying made sense.

Thanks again.

Best regards

Jonathan

Hi Andrew,

I have a question regarding the use of Prophoto RGB. Lightroom doesn't give you the option of using anything else but I'm struggling to see why it exists. You commented about future proofing your images in case technology improves but this seems redundant to me as it's virtually impossible to know how those currently invisible colours affect the overall image.

Would it not be better to make your adjustments in the widest colour space you can see on screen (Adobe RGB) and keep the RAW files as future proofing? This seems like it would allow you to convert down if needed whilst still giving control and predictability over the final image. Am I missing something here?

Hi Andrew,

I have a question regarding the use of Prophoto RGB. Lightroom doesn't give you the option of using anything else but I'm struggling to see why it exists.

Lightroom's processing color space is based on ProPhoto RGB but you can encode in any color space it supports upon export or rendering.

If you process based upon the limitations of a display gamut, you funnel colors you can capture and output elsewhere to that one device. I don't see how that's useful.

Lightroom doesn't give you the option of using anything else but I'm struggling to see why it exists.

I'll certainly defer to Andrew on the details, but the principle is never to throw out data unless you have to. The software will render the image in a reduced gamut as needed. For example, it will use sRGB to display on your monitor if that's all you have.

Lightroom's processing color space is based on ProPhoto RGB but you can encode in any color space it supports upon export or rendering.

If you process based upon the limitations of a display gamut, you funnel colors you can capture and output elsewhere to that one device. I don't see how that's useful.

I suppose my reasoning on why it's useful is that, it would provide a much more accurate and predictable representation of what will be output, if for eaxple, it were sent to a printer profile like the one used in Andrew's video. Such a profile has the potential to render colours which you haven't accounted for because you couldn't see them when you made your adjustments. The only way I can see you making use of those colours outside the gamut of your display, but inside the gamut of your printer would be to print tests and then try to make adjustments from them but that seems like a very inefficient way of working to me.

The software will render the image in a reduced gamut as needed. For example, it will use sRGB to display on your monitor if that's all you have.

Could there be the possibility to introduce banding (8 bit files), if your using a very wide gamut profile to make adjustments for an output device with a significantly smaller gamut?

the principle is never to throw out data unless you have to

The problem I see with this practice, is that this is data you have no way of visualizing, so to my mind it becomes redundant. If it became available at a later date, you may just as well reprocess the raw file. It seems more logical to me to work with what you have at the present time, work in a space you can see to avoid potential anomalies when sent to it's output.

The problem I see with this practice, is that this is data you have no way of visualizing, so to my mind it becomes redundant. If it became available at a later date, you may just as well reprocess the raw file. It seems more logical to me to work with what you have at the present time, work in a space you can see to avoid potential anomalies when sent to it's output.

You're working on a control like Saturation or Vibrance. As you move the slider, the results stop showing, because the edits are beyond the gamut of your display. STOP.

Fact of life: There are colors you can output beyond the gamut of even a wide gamut display. You want to use them or clip them all to fit into a display gamut?

NO printer can print all of the sRGB color gamut, let alone wider gamut RGB Working Spaces. There are colors (color numbers) you can't see on a display you can produce elsewhere. There are colors that can be displayed on a display that can't be printed.

You're working on a control like Saturation or Vibrance. As you move the slider, the results stop showing, because the edits are beyond the gamut of your display. STOP.

We're talking about the same thing here, by stopping when you no longer see changes, you are working within the gamut of your device. I think this is the right way to work.

Fact of life: There are colors you can output beyond the gamut of even a wide gamut display. You want to use them or clip them all to fit into a display gamut?

NO printer can print all of the sRGB color gamut, let alone wider gamut RGB Working Spaces. There are colors (color numbers) you can't see on a display you can produce elsewhere. There are colors that can be displayed on a display that can't be printed.

I agree 100%, I think I acknowledged the differences between profiles. The only point I'm making is that you should work within the largest gamut that your screen and your output can display. If you're intended target is another monitor then it makes more sense to me to edit in SRGB. Otherwise, all those colours that sit outside this gamut will be assigned a nearest value and you'll lose subtly in the gradations at the edges of the spectrum. The same way you would with your blacks and whites.

A calibrated monitor in a color-managed system should display colors correctly regardless of the color space assigned to that image. Correctly enough, at any rate, so that you can edit the color, and it will look resonably the same on your monitor and my monitor, even if they are diverent brands and models.

Monitor and print profiles have the same structure as standard color space profiles, and can be applied directly to the image. However the correct usage is to embed a color space profile in the core image, while the print and monitor profiles interpret the image so that it displays correctly, based on the nature of the device.

Photoshop books by Martin Evening have an excellent dissertation on color and color space, with diagrams which show how and where profiles are applied.

The only point I'm making is that you should work within the largest gamut that your screen and your output can display.

We disagree. But go ahead. I have a wide gamut display. It's not wide gamut enough and never will be. There will never be a ProPhoto RGB gamut display; never. I simply refuse to clip colors I can't see on a display but can output on my various wide gamut printers. You can clip colors if you so desire. For me, the proof is in the print. And the print is important.

We disagree. But go ahead. I have a wide gamut display. It's not wide gamut enough and never will be. There will never be a ProPhoto RGB gamut display; never. I simply refuse to clip colors I can't see on a display but can output on my various wide gamut printers. You can clip colors if you so desire. For me, the proof is in the print. And the print is important.

We're not disagreeing.

The only point I'm making is that you should work within the largest gamut that your screen and your output can display.

You're working with the largest gamut that your screen and your output can display. We're using the same terminology, you're also describing your printer as your output and using your prints to judge the adjustments you make.

For me, the proof is in the print.

I'm coming at this more from the stand point of someone who doesn't have instant access to a wide gamut printer or more likely that the images will go directly online.

Thanks for your help, I do appreciate it, once again the video link was very helpful.

Best regards.

Jonathan

Hi Andrew,

I found several other videos you've made, so it does seem that you're right we are disagreeing. I'm going to watch the videos and see if I can get a better understanding of what you're describing, you're obviously far more knowledgeable on this subject than I am so I'd like to learn where my thinking is off.

Why can't a monitor be made that exceeds the gamut of the best possible printer? It seems like pigments on paper would be more limiting than something that generates colored light. Is there some fundamental limitation or is it just we don't have the tech yet?

We all have to live with a disconnect between the simple shapes of RGB working space and the vastly more complex shapes of output color spaces to the point we're trying to fit round pegs in square holes. To do this, you need a much larger square hole.

Simple matrix profiles of RGB working spaces when plotted 3 dimensionally illustrate that they reach their maximum saturation at high luminance levels. The opposite is seen with print (output) color spaces. Printers produce color by adding ink or some colorant, while working space profiles are based on building more saturation by adding more light due to the differences in subtractive and additive color models. To counter this, you need a really big RGB working space like ProPhoto RGB again due to the simple size and to fit the round peg in the bigger square hole. RGB working spaces have shapes which are simple and predictable and differ greatly from output color spaces. Then there is the issue of very dark colors of intense saturation which do occur in nature and we can capture with many devices. Many of these colors fall outside Adobe RGB (1998) and when you encode into such a color space or smaller gamut, you clip the colors to the degree that smooth gradations become solid blobs in print, again due to the dissimilar shapes and differences in how the two spaces relate to luminance. So the advantage of ProPhoto isn't only about retaining all those out-of-gamut colors it's also about maintaining the dissimilarities between them, so that you can map them into a printable color space as gradations rather than ending up as blobs. 


Here is a link to a TIFF that I built to show the effect of the 'blobs' and lack of definition of dark but saturated colors using sRGB (Red dots) versus the same image in ProPhoto RGB (Green dots). The image was synthetic, a Granger Rainbow which contains a huge number of possible colors. You can see that the gamut of ProPhoto is larger as expected. But notice the clumping of the colored red vs. green dots in darker tones which are lower down in the plot. Both RGB working space were converted to a final output printer color space (Epson 3880 Luster).

http://www.digitaldog.net/files/sRGBvsPro3DPlot_Granger.tif

Link works here, but below is what you'd see:

http://www.digitaldog.net/files/sRGBvsPro3DPlot_Granger.tif