Thanks again Aaron. I printed up the i1P samples and am going to let them dry overnight and shoot them tomorrow alongside the other samples, and will post the results. For the moment though, Argyll remains the most impressive with the Z3200, followed by DropRGB.
Andrew, if you’re still around, I’m getting darker blue balls with i1P than I expected. You might want to check that out in my pics tomorrow. Not as dark/black as Copra, but much darker than those in your video, particularly in the darker ball. I suspect it’s more likely a result of the inkset used by the Z, or possibly that we used i1P’s default settings, than an error in color management as I’ve been over the latter’s pipeline quite a few times. But very interested in your take on that. I’ll get a little better light on the final shot too because there is clear gradation in the i1P blue sample that’s not at all so clear in Copra’s and the darks in all of them simply need more light in the shots.
Hi Brad,
This is a topic worth further discussion as it shows some of the risks using a large colorspace that extends to imaginary colors and the "blue" ball on the bottom right of Andrew's Gamut_Test_File_Flat.tiff image represents the most extreme, and imaginary, RGB blue. Load the file in Photoshop, bring up the info panel, and select Lab as the colorspace to show. Move the cursor to different parts of the blue ball. Notice the L* stays below 1 (.1 actually - even for max blue) which is a luminance below all printable blacks. The ICCLAB value of ProPhotoRGB(0,0,255) is L*=.08, a*=90, b*=-128. (ICCLAB clips CIELAB at -128, Actual CIELAB b*=-172).
So why does even ProPhotoRGB(0,0,255) look blue at all on a monitor if it's so dark?
The answer is that ProPhotoRGB colors are converted to displayable colors. Taking the specific cases of displays that are close to sRGB and those close to Adobe RGB, here is what we get: Both displays will attempt to display RGB(0,0,255). An sRGB like display will show LAB=30,68,-112 while Adobe RGB wiil do LAB=30,69,-114. These are close because the "blue" of Adobe RGB and sRGB are the same. They are also well defined since ICC specifies the math to be used when converting matrix profile colorspaces.
But what color should a printer make? These are way beyond printable gamuts. Generally, profile software in Perceptual tries to preserve hue or hue and luminance. In the latter case the printer will print black. This is what causes the big differences between how profiles handle these colors. And a printer profile operates only on ICCLAB values.
My 9800 glossy profile converts ProPhoto(0,0,255) to LAB(16,18,-56), a printable blue but much darker than what my monitor shows. Is that the "right" color? Who knows?
So this brings up the more general issue of what colors should we be working with. I generally put these in several categories from the narrowest set, those that the printer can print, to increasingly larger gamuts.
These are stimulus colors. Colors are perceived based on context. That is what stimulus colors surround them and what adaptation has occurred.
1. Colors that are actually printable. By definition, these colors are within the printer's gamut.
2. Colors that can exist, theoretically at least, on a surface. These are the set of all colors with completely arbitrary spectral reflectances, and are bounded by the MacAdam limits. They are more limited than all possible visible colors because they are formed by subtraction of wavelengths. In a sense, these might be considered the limits of a "perfect" printer with an infinite set of inks.
3. Colors that exist and can be created by mixing all possible wavelengths of light. These require emissive sources. Think mixing light from a large number of lasers, each with a slightly different visible wavelength and adjustable magnitudes.
4. Finally, there are the imaginary colors. These are colors with xy coordinates that are outside the stimulus gamut. They don't exist because there are no combinations of wavelengths at any magnitude that produce them. These are the ones outside the classic CIEXY horseshoe gamut most often encountered in ProPhoto RGB where the Green and Blues are imaginary.
When evaluating a profile, my criteria varies. It's most critical for in printer gamut colors. There shall be no visible banding or other anomalies for these. Next, are Mac Adam colors that are outside the printer's gamut but physically realizable. These should be rendered smoothly and be pleasing though they will not be accurate. Then there are colors that are real but not possible on a surface. How they are rendered is not something I care about too much though my preference is that hue be maintained. These, can't ever be printed but can appear in photographs with things like red LED Christmas lights . I expect the luminance and saturation to drop but the hue to remain close.
Andrew's profile stress test image is particularly useful as it contains a variety of all of these. The photos are near what printer gamuts can reproduce and the synthetics push things out further past MacAdam and imaginary color limits. He has a good video of this showing how to edit real, but saturated images pushing the printer's gamut to recover blocked colors.
By way of example I've attached a down sampled color coded mapping of Andrew's stress test image showing the colors that are in each of these 4 categories.
The color assignments are:
1. pale cyan: Colors inside the printer's gamut. This varies of course, I used my 9800 with an Epson Prem. Glossy for this.
2. blue: Colors that are physically realizable on a surface (within MacAdam limits) but not printable with my printer.
3. red: Colors that physically exist (within the human gamut) but only with emissive sources like lasers, leds, etc.
4. black: Imaginary colors. They don't exist but are useful mathematical constructs.