These are my notes from a small experiment to investigate the properties of profiles that i1Profiler creates. It's going to be a bit long, as I continue to update this thread with further investigation.Nobody tells us exactly what these sliders do. What exactly do they change? What are the downsides to these changes? Do we have to sacrifice some gamut for more smoothing, or maybe a higher dmax for a neutral grayscale? Under what circumstances are the changes useful? When are they irrelevant? Are there optimal values and suboptimal values for each slider? (That is, say never set the smoothness slider at XX value because the profile’s printing gamut suddenly becomes all wonky from a bug.) Do certain combinations of slider settings do things that are undesirable, hurt the profile quality, or maybe improve things beyond your wildest imagination?
I would like to clarify that I am not a color expert, or mathematician or scientist or the sort, so if anyone spots an issue that is technically flawed, I will be very happy to retract my statements, and I will re-investigate that aspect again.IntroductionAndrew Rodney, in a review of the i1Profiler software on the luminous landscape website
, stated that “many of the provided sliders [in the "Profile Settings" module] produce tiny, almost insignificant differences from each end of the slider scale”. “Building profiles with both extremes for the Smoothness slider produced results that were less than a max deltaE of 1”. With all due respect to Andrew, I believe him.
I am curious if I can see a difference between various settings of the sliders when building RGB printer profiles. I made a series of profiles, from a measurement file I scanned from a target I printed, with varying inputs of the following sliders found in the “Profile Settings” module: Contrast, Saturation, Neutralize gray, and Smoothness. These sliders affect the rendering of the perceptual table of the printer profile. I am using i1Profiler version 1.3.2.
These settings remain constant for all the test profiles I generated. For "Tables", “Size A to B” is set to “Large”, “Size B to A” is set to “Large”, and “Granularity” is set to “16 bit”. Under "Advanced", “Chromatic Adaptation” is left at “Bradford”, a pointless setting since my illuminant used in the “Lighting” module is D50. ICC profile version is Version 2, and “Profile White point” is “Default”.How I Made my Observations
Be aware that many of the following observations are SUBTLE. One method I use to better see the difference is to convert a granger rainbow with a sidebar neutral grayscale target (so I can see the effect on grays too) to various test profiles, layer the results in a non-color managed document, and use the difference blend mode and a strong curve adjustment to see where changes have occurred. An example of the target is attached.
I also use the ‘flash to compare’ method, where I create a custom proof setup for a test profile, and then change the proof settings to another test profile. Checking and un-checking the ‘preview’ checkbox ‘flashes’ the view. One method to judge the gamut of the profile would be to activate the gamut warning overlay together with a proof setup using the profile in question on a granger target in ProPhoto RGB color space. This is done in Photoshop.
I have looked at the Smoothness thus far, and will work on the others soon.Observations from Studying the Test Profiles
I created test profiles with the following inputs for the Smoothness slider, while Contrast, Saturation and Neutralize Grayscale were set to 0:
0, 10, 20, 30, 40, 50, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 90, 100.
When the “Smoothness” slider is set to zero, the resultant printer profile has the largest gamut. When it is set to 100, the gamut is much smaller. I do not know why the gamut has to shrink, but at this point, to my mind, one has to sacrifice gamut for smoothness. But it’s not so simple, more on that later.
Comparing 0 and 100, the profile with smoothing at 100 is visibly smoother mostly in the light yellow-green (I’m thinking sunlit grass, foilage) color areas. Reds are also visibly smoothed across most of the range. Oranges are affected to a lesser degree. Blues were somewhat smoother, mostly in the darker regions, but it's the most subtle change.
Looking at the gamut, in intervals of 10, it shrinks from 0 to 10, 10 to 20 and 20 to 30, but increases from 30 to 40 and 40 to 50 (but less so), then decreases from 50 to 60 (60 being smaller than 30), and continues to do so for 70, 80, 90 and 100. Still it is not so simple. Look at settings spaced 1 value apart.
It is interesting to note at this point that there are no changes to neutral gray tones until the smoothing slider hits 61. They remain unchanged at 0, 10, 20, 30, 40, 50 and 60. I didn’t try out settings in between those values, but I’m assuming that they do not change then too.
Smoothing Slider from 60 - 70
Ok, so the gray values are the same until 60. At 61, they lighten. It is mostly seen in the middle regions of the grayscale. From 62 to 63, they do NOT change at all, when compared to 61. Very interesting. Grays get darker going to 64, and lighter at 65. 64 compared to 60 is almost the same, with a 1 value change in one R, G or B channel only. From 66 to 69, gray values are almost the same as 65, with a 1 value change in one R, G or B channel only. Gray values lighten at 70. When I say 1 value change in one R, G or B channel only, I mean something like R130 G128 B126 changes to R130 G129 B126.
The profile gamut increased from 60 to 61, decreased going to 62 (62 almost identical to 60), increased at 63 (bigger than 61), decreased at 64, increased at 65 (bigger than 61 and 63), and decreased gradually from 66 to 67, 68, 69 and 70.
Smoothing Slider from 70 - 80
Gray tones get lighter from 70 to 71. From 71 to 79, increasing smoothing by a value of 1 resulted in minimal changes to grays. No more general lightening or darkening. Most grays do not change. Those that do exhibit a 1 value change in one R, G or B channel only.
Profile gamut increases from 70 to 71 (note that 71 gamut is greater than 61), decreased at 72 (72 slightly smaller than 70), decreased at 73 (by a very small amount), increased at 74 (very slightly too; 74 only slightly larger than 72), increased at 75, and more or less decreased (tiny differences) from 75 to 76, 77, 78 79 and 80.
Note that the gamut of the profile when Smoothness is set to 71 is larger than when it is at 61. So the assumption that gamut gets smaller when increasing the smoothing amount is not always true. Sometimes it increases. But 100 is much smaller than 0.
This is very very interesting behavior to me.