A 2D map can be made where each point on the map represents the relative fraction of increased illuminance from all the colors that are close enough to significantly reflect back to frosted LED bars and on to the scanned point. However, while if fixes most of the errors that go into making profiles, it does not fix errors from subsequent scans of other images.īut something similar can be done. This processing can be done quite automatically and should produce much better profiles.
EPSON SCANNING TOO BRIGHT PATCH
Then the patches' XYZ values can be proportionally increased by the total increased illumination the patch is receiving to arrive at an XYZ representing the patches' color were it to be illuminated properly. Since patch coordinates are regular, the scanned values, converted to linear XYZ, can be multiplied by the fraction that represents their contribution which is a fixed function of geometry. This, it turns out, offers a mathematical way to compensate for the scanner's extra reflected light. After that distance the errors drop by over 90%. This is a problem creating scanner profiles as the scanned RGB values are a function of the patch color as well as the colors of patches within about 1/3 inch of it horizontally and about 1/2 inch vertically. This is entirely consistent with light from the illuminated areas of the paper reflecting back onto the frosted light sources, which are quite close to the paper, and effectively increasing the illumination the paper gets at the scan location.
But it doesn't affect black patches very much at all because a patch with L* of 4, illuminated by 25% more light, only goes up to 5. The amount of light difference in the two examples I gave is about 25% (in linear space such as nits, lux, etc.). Negligible effect scanning transparencies. It's purely an effect of bright areas of the paper reflecting light back down on the horizontal frosted illumination strips which then increases the light seen by the scanned portion. One positive note: This does not apply to scanning film. The scanned color of IT8 or any other patch set has a fixed set of patch locations so the impact of adjacent patches is baked into the profile and results in "good" readings on the same patches as those were what the profile was created from. It doesn't show up in the normal dE scan tests because dE is reported self referentially. Arguably, replication by colorimetric means is going to introduce large errors if the profile is generated from patch sets with different spectra than the scanned object but this just adds error. But the other issue is inability to colorimetrically replicate an original. This can be mitigated by setting the "Scale" factor in Argyll's colprof. Clipping of near whites, which is highly likely when scanning papers with high white L* over 96 with subtle high key tones.
Prepare to see something like values of 89 and 99, or possibly higher levels like 94 and 100, if the whites are clipping above 100. Scan them with a profile that doesn't clip the whites and examine the L* of the white patches in the center of each square. On the second insert a centered 3.5" by 3.5" white square.
On the first insert a centered, 0.1" white square.ģ. Create an image with 2, 4" by 4" black squares.Ģ.
Given the magnitude of a potential error, the visual effects are usually subtle but result in a slightly off copy when using the scanner for critical reproduction purposes.ġ. It is clearly due to light, reflecting off the paper and back onto the two frosted, LED light sources which then illuminates that portion of the paper which is being scanned. I see as much as a L* difference of 10 for highlights depending on what colors are around, and how close they are to the highlights.