Question about tone remapping with Relative Colorimetric Rendering
I'm trying to understand how tones are remapped when going from file to print, using an RGB driver. I'll use an example so my question is clear. I created a black to white gradient in Photoshop, Adobe RGB. 11 step posterization. I purposely chose to keep color out of this test, since I wanted to keep it simple to understand how the luminance values get mapped. That gives RGB numbers, from dark to light, of 0 25 51 76 102 128 153 178 204 229 255. The info palette shows L* values of 0 6 20 32 43 54 64 73 83 91 100. I *converted* the file to a custom RGB profile (using the epson printer driver), Relative Colorimetric, BPC on, of a weak Dmax matte fine art paper. This paper achieves about 18L* for Dmax and has a white of about 96L*. I chose a weak paper on purpose to amplify the effect. The info palette shows changes in the two darkest patches ONLY. Black goes from L* of 0 to 2, and the next lighter patch goes from 6 to 8. All other patches remain the same. The RGB numbers change too reflecting profile tables to adjust brightness and neutrality. I believe these are the new RGB numbers that will be sent to the printer driver, correct? They obviously aren't the achieved values in the print, because the paper can achieve only 18L* black and 96L* white. Is there a way to know what the final L* values in the print will be using Photoshop, or in looking at the profile? If so, how? I assume this information must be in the profile. (I built this printer profile using i1Profiler). OK, switch to the original RGB numbers (before conversion) and go to Proof Preview instead of Convert to Profile. If I proof preview using RC intent, BPC turned On, the file display shows the two darkest patches brightening up (same as the conversion). However, since I am not converting, the numbers in the info palette are the original numbers. Still in Proof Preview, RC, BPC On, if I turn on Simulate Black Ink, the entire tonal scale lightens up, most notably, from blacks to the midtones, but even a little bit in the 1/4 tones. Obviously, the profile knows this, but it doesn't show me the numbers. If I then turn on Simulate Paper White, the display reflects the dingy yellow-white of the paper (96L/0a/3b or so). Now, the light end of the tonal scale is scaled back, giving a more accurate view of the real tonal range of the final print. Unfortunately, the numbers in the info palette still show the original numbers. Is there a way to see the final numbers I would read in the print if using a spectro (assuming a perfect profile, of course)? Sorry for the long email, but I want it to be clear. RC Intent has always been described as accurately reproducing in-gamut colors, then clipping all out-of-gamut colors and tones, bringing them back to the edge of the destination gamut. Obviously, the whitest white this paper can produce is 96L/0a/3b, and the blackest black is 18L*/0a/0b. Here's the real question...Will all the grayscale tones in my step wedge from 18L to 96L reproduce accurately on the final paper using RC Intent? Or will they be scaled somehow? The Proof Preview shows them ALL changing. And will my two black patches (original numbers of 0L and 6L) both end up being 18L? Again, the proof preview says No. I'd like to believe the midtones will stay locked, so 50L in my info palette will read 50L in the print, but I am not convinced this is the case. Thanks for any responses, and sorry again about the length of this email. I hope it was clear. Lou Dina
What are your conversation options set to in the color settings? AbsCol? Oh, can you repeat all of this without using the word "accurate"? :-) Scott Martin On Jun 1, 2013, at 9:35 AM, Louis Dina <lou@loudina.com> wrote:
I'm trying to understand how tones are remapped when going from file to print, using an RGB driver. I'll use an example so my question is clear.
I created a black to white gradient in Photoshop, Adobe RGB. 11 step posterization. I purposely chose to keep color out of this test, since I wanted to keep it simple to understand how the luminance values get mapped. That gives RGB numbers, from dark to light, of 0 25 51 76 102 128 153 178 204 229 255. The info palette shows L* values of 0 6 20 32 43 54 64 73 83 91 100.
I *converted* the file to a custom RGB profile (using the epson printer driver), Relative Colorimetric, BPC on, of a weak Dmax matte fine art paper. This paper achieves about 18L* for Dmax and has a white of about 96L*. I chose a weak paper on purpose to amplify the effect.
The info palette shows changes in the two darkest patches ONLY. Black goes from L* of 0 to 2, and the next lighter patch goes from 6 to 8. All other patches remain the same. The RGB numbers change too reflecting profile tables to adjust brightness and neutrality. I believe these are the new RGB numbers that will be sent to the printer driver, correct? They obviously aren't the achieved values in the print, because the paper can achieve only 18L* black and 96L* white.
Is there a way to know what the final L* values in the print will be using Photoshop, or in looking at the profile? If so, how? I assume this information must be in the profile. (I built this printer profile using i1Profiler).
OK, switch to the original RGB numbers (before conversion) and go to Proof Preview instead of Convert to Profile. If I proof preview using RC intent, BPC turned On, the file display shows the two darkest patches brightening up (same as the conversion). However, since I am not converting, the numbers in the info palette are the original numbers.
Still in Proof Preview, RC, BPC On, if I turn on Simulate Black Ink, the entire tonal scale lightens up, most notably, from blacks to the midtones, but even a little bit in the 1/4 tones. Obviously, the profile knows this, but it doesn't show me the numbers.
If I then turn on Simulate Paper White, the display reflects the dingy yellow-white of the paper (96L/0a/3b or so). Now, the light end of the tonal scale is scaled back, giving a more accurate view of the real tonal range of the final print. Unfortunately, the numbers in the info palette still show the original numbers. Is there a way to see the final numbers I would read in the print if using a spectro (assuming a perfect profile, of course)?
Sorry for the long email, but I want it to be clear. RC Intent has always been described as accurately reproducing in-gamut colors, then clipping all out-of-gamut colors and tones, bringing them back to the edge of the destination gamut. Obviously, the whitest white this paper can produce is 96L/0a/3b, and the blackest black is 18L*/0a/0b.
Here's the real question...Will all the grayscale tones in my step wedge from 18L to 96L reproduce accurately on the final paper using RC Intent? Or will they be scaled somehow? The Proof Preview shows them ALL changing.
And will my two black patches (original numbers of 0L and 6L) both end up being 18L? Again, the proof preview says No. I'd like to believe the midtones will stay locked, so 50L in my info palette will read 50L in the print, but I am not convinced this is the case.
Thanks for any responses, and sorry again about the length of this email. I hope it was clear.
Lou Dina _______________________________________________ Do not post admin requests to the list. They will be ignored. Colorsync-users mailing list (Colorsync-users@lists.apple.com) Help/Unsubscribe/Update your Subscription: https://lists.apple.com/mailman/options/colorsync-users/scott%40on-sight.com
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On Jun 1, 2013, at 10:35 AM, Louis Dina <lou@loudina.com> wrote:
RC Intent has always been described as accurately reproducing in-gamut colors, then clipping all out-of-gamut colors and tones, bringing them back to the edge of the destination gamut.
All bets are off when you turn on black point compensation....BPC scales the black point of the source to the black point of the destination instead of clipping.....it also has a subtle effect on colors as well. If you want *accuracy*, use absolute colorimetric.....and as Scott eluded, have your color settings prefs set to absolute as well if you want a accurate readout in the info palette. Terry
participants (3)
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Louis Dina
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Scott Martin
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Terence Wyse