IT8.7 Profiling Tests — Continued

(And as all the other images here, it is converted to 8 bits/channel sRGB and jpg'ed at quality setting 8.)

Overall, it does not look so bad, but if you look close, you can see that the grey patches are not neutral, and the darkest patches are wrong in all three Lab coordinates.

GS0 for instance (the clear film patch), gets Lab coordinates [89, 1, 1], which is about 1 or 2 units off from the reference file value [90.49, 1.03, 1.05]. Not much to worry about, but:

GS22 (the black just to the left of the white line) should be [1.64, 0.66, -0.05] in Lab coordinates. Measurements show about [5, 2, 2], however, so not only is it too bright, it is not neutral. The difference in 'L' between patch GS22 and GS21 should be 2.0, and another 2 units to patch GS20. With the SilverFast profile, however, we only get a difference of about 1 unit between these patch pairs, so the shadows are heavily compressed (and not neutral!). This is also precisely my experience when scanning slides! (All these values were read before sRGB and 8 bit conversion, since it sometimes differ about 1 unit and I want the most accurate ones.)

It's a really good result with no artifacts! If you compare this with the SilverFast version, you can see that the very pale patches A13-A19 are much better here — bright but still with some color! In the SilverFast version, the patches are almost washed-out (despite they are very far away from RGB 255) — they should have been both brighter and have more color. inCamera makes them just about perfect!

The only patch I found that was slightly off, was F8, which should have been [45.18, -64.70, 23.43] but it was around [45, -62/-63, 22/23], so the a-value was a bit off. Also J4, L15 could be found to be just barely 2 units off in one of the 'a' or 'b' components.

As explained in it8tests.shtml, the profile was made by the author of Scarse from an image of lower resolution (about 1 Mpixel TIFF images) in December 2003. Both age (one year ago) and lower resolution may perhaps cause some deviations. However, I have compared this image with the one-year-old image that was used to create the profile, and when both images are assigned that profile, there are no visible differences at all!

So, even though it may not be 100% accurate to compare this one with the inCamera version, the test supports the conclusion that the differences I see between Scarse and inCamera are significant, and are basically not caused by a difference in resolution of the scan used to produce the profile. So, I make the following claims:

Overall, it looks similar to the inCamera version. But the most striking difference in visual appearance (looking at both images in Lab mode before sRGB conversion) is that the whole yellow column 15 is much less saturated in the Scarse version. Also, the pale patches A13–A19 are almost completely washed-out! (The visual appearance is here about the same before as after conversion to sRGB.) Patches B8, D12 and G22 are very different between inCamera and Scarse, and the whole area A2–L4 clearly change appearance when you swap the two windows back and forth.

Patch GS22 has the right L-value, but it is a bit off in the a/b values, and patches GS22 and GS23 has the same L-value, but it should differ 1 unit. So the dark shadow performance has some problems here.

The Scarse profile did pretty well, but it has som problems. It is worth a closer inspection, and it does certainly have potential.

The SilverFast profile is not recommended at all. As long as it is based on the preview of the scan, it does not have any potential. The HDR version of SilverFast, however, may have potential, since it works very differently.

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