Issue with unexpected Blue Channel Clipping, SF Ai
PostPosted: Thu Jun 02, 2011 1:29 pm
I have a Plustek 7500i Ai. First of all, I'd like to say that I like Ai software and know how to use it. There are unfortunately some unexpected behaviours, that are annoying. This is one is the worst and I cannot figure out how to fix it. When I scan in 3600 DPI, the colors of the Ai preview and the colors of the file opened in OSX Preview or Photoshop match. If I scan the same exact frame with maximum resolution for my Plustek of 7200 DPI, I get a blue color cast on the final image. It took me quite a bit of time to pinpoint, why this happens and I would like to share and see if this has been experienced by anyone else, what the reason is, and if there is a fix.
Onto the fun part then. Please look at the blue channel and what happens to it in 7200 DPI scan.
This is the preview window of 3600 DPI scan:
This is the resulting image, the blue channel looks exactly how it should — the same way as in Ai:
Another preview, it's all the same, just changed the resolution to 7200 DPI:
And here's the resulting image, as you can see, the blue channel for some reason gets stretched a bit to the right and that introduces a blue cast:
Just to get this out of the way, yes I have deleted the preferences and reinstalled Ai, this did not make a difference.
Here's another more drastic example. In this scan I deliberatly ask Ai to reduce blue channel contrast and squeeze its histogram by changing the highlight output value, check out what happens.
Scan shot, asking to reduce blue channel contrast:
Resulting image scanned at 3600 DPI, blue channel looks as expected:
Resulting image scanned at 7200 DPI, what is this??! Looks like someone took a bite out of the blue highlights!
So, any ideas what the culprit is?
Onto the fun part then. Please look at the blue channel and what happens to it in 7200 DPI scan.
This is the preview window of 3600 DPI scan:
This is the resulting image, the blue channel looks exactly how it should — the same way as in Ai:
Another preview, it's all the same, just changed the resolution to 7200 DPI:
And here's the resulting image, as you can see, the blue channel for some reason gets stretched a bit to the right and that introduces a blue cast:
Just to get this out of the way, yes I have deleted the preferences and reinstalled Ai, this did not make a difference.
Here's another more drastic example. In this scan I deliberatly ask Ai to reduce blue channel contrast and squeeze its histogram by changing the highlight output value, check out what happens.
Scan shot, asking to reduce blue channel contrast:
Resulting image scanned at 3600 DPI, blue channel looks as expected:
Resulting image scanned at 7200 DPI, what is this??! Looks like someone took a bite out of the blue highlights!
So, any ideas what the culprit is?