tldr; Has anyone using Silverfast software noticed edge ringing in prescan images that seem to affect automatic colour correction?
I've been using Silverfast 8 and now 9 for a while. Currently I'm scanning thousands of family slides.
Just recently I noticed a problem with prescans.
I use an Epson V800 flatbed scanner. I do my prescans at high res x4. I am prescanning a set of slides in a slide holder.
Example of slide holder layout
If I have some relatively high contrast edges, a prescan produces edge artifacts. Below is an example.
On the left is a prescan image. You can see the darker ringing where the white tree meets the darker BG. You can also see a sampler on the left of the image, labelled with a B. This is the point where the Silverfast automatic blackpoint picked. It has clearly picked a position with the BLACK ringing.
The right hand image is the slide scanned at full res, full colour depth, everything. Just to demonstrate that the ringing is not in the original slide.
Left: Prescan image at x4, showing ringing around bright to dark areas. RIGHT: full res scan to show the problem is not in the original
This would not really be a problem, except that the automatic colour correction tools seem to be using the blown up prescan, with the artifacts, to get blacks and whites. This will produce incorrect corrections, because the artifacts are from filtering, and blowing the image up.
If the automatic tools were using the original prescan image size, or a blown up version using a filter that doesn't produce edge artifacts, then I expect it would be fine.
I work in VFX, so I'm familiar with various filters and the kinds of artifacts they can produce. And what I'm seeing in the prescans are artifacts for filters like sinc, lanczos and similar.
In order to not get those artifacts it needs a filter like cubic, or bicubic I expect.
I have been having a conversation with a Silverfast support person, back and forth.
And he insists that Silverfast uses a bicubic filter for enlarging the prescans. That may be true for enlarging them to view on a monitor, inside Silverfast.
But I cannot see that as true for whatever enlargement is being done when sampling is taking place.
I don't know if I am missing something fundamental. Or if we are communicating badly.
Its possible that English isn't his first language (since its a German company) so I am trying to ask clearer questions, without being insulting with too simple language... :-/ Tech support is hard enough without subtle language differences causing confusion.
In any case, if anyone has any insight into this, I'd be very grateful.
Cheers
I've been using Silverfast 8 and now 9 for a while. Currently I'm scanning thousands of family slides.
Just recently I noticed a problem with prescans.
I use an Epson V800 flatbed scanner. I do my prescans at high res x4. I am prescanning a set of slides in a slide holder.
Example of slide holder layout
If I have some relatively high contrast edges, a prescan produces edge artifacts. Below is an example.
On the left is a prescan image. You can see the darker ringing where the white tree meets the darker BG. You can also see a sampler on the left of the image, labelled with a B. This is the point where the Silverfast automatic blackpoint picked. It has clearly picked a position with the BLACK ringing.
The right hand image is the slide scanned at full res, full colour depth, everything. Just to demonstrate that the ringing is not in the original slide.
Left: Prescan image at x4, showing ringing around bright to dark areas. RIGHT: full res scan to show the problem is not in the original
This would not really be a problem, except that the automatic colour correction tools seem to be using the blown up prescan, with the artifacts, to get blacks and whites. This will produce incorrect corrections, because the artifacts are from filtering, and blowing the image up.
If the automatic tools were using the original prescan image size, or a blown up version using a filter that doesn't produce edge artifacts, then I expect it would be fine.
I work in VFX, so I'm familiar with various filters and the kinds of artifacts they can produce. And what I'm seeing in the prescans are artifacts for filters like sinc, lanczos and similar.
In order to not get those artifacts it needs a filter like cubic, or bicubic I expect.
I have been having a conversation with a Silverfast support person, back and forth.
And he insists that Silverfast uses a bicubic filter for enlarging the prescans. That may be true for enlarging them to view on a monitor, inside Silverfast.
But I cannot see that as true for whatever enlargement is being done when sampling is taking place.
I don't know if I am missing something fundamental. Or if we are communicating badly.
Its possible that English isn't his first language (since its a German company) so I am trying to ask clearer questions, without being insulting with too simple language... :-/ Tech support is hard enough without subtle language differences causing confusion.
In any case, if anyone has any insight into this, I'd be very grateful.
Cheers