Is "48 bit HDR color" raw data for a "negativ

[pdv]

I'm trying to get raw data from an epson 4990 using SF-Ai (in demo-mode) when scanning negatives (on Mac OS X).

When using the "48 bit HDR color" mode I expect the same result whether I use the "positive" or the "negative" setting, but it isn't.

So it looks like some processing is taking place for at least one of the 2 possible settings (probably for the "negative").

[LSI_Magnussen]

When scanning in negative mode, the SilverFast version for the Epson scanners will lengthen the exposure to achieve as good scans with as less noise as possible. This results in longer scan times.
If this is not what you want and to let SilverFast scan negatives in the same way as positives, enable "Scan Draft" under Options->Special.

Regards
Ralf

[pdv]

Thanks for clarifying and obviously I prefer the standard "negative" setting.
However it sets me wondering whether any other settings (like the settings in the negafix panel) have an influence on the "raw" data when scanning negatives.

Making a series of testscans (all with "48 bit HDR color" and standard "negative" settings) I almost always got exactly the same result, but not always, although I could not easily pinpoint what makes the difference. Sofar my best observation is that the first scans made after starting up SF-Ai (this is based on a previous prescan) are of one kind. As soon as I touch e.g. the "Auto tolerance" slider then the next scan will be (slightly) different. But any further scans are then always similar wathever the (negafix) settings. The only way to switch back to the first result is starting up SF-Ai all-over again. Which of these is the correct one?

[LSI_Magnussen]

You should get different scan results when you see/make changes in the Negafix histogram(s) found in the Expansion panel of the Expert part of the Negafix dialog.

Best regards
Ralf

[pdv]

Thanks Ralf, I think I more or less understand it now.
The HDR-file contains the effect of the "orange mask" settings (expansion dialog) but not those of the levels dialog.
When turning off the automatic mask removal completely (with the reset button) then the resulting HDR-file is exactly the same as when scanned as a positive (and apparently the longer exposion you've mentionned is then also not active).
I've still a minor issue: when recalling saved frame-settings the histograms in the NegaFix-Expansion dialog are not updated immediately (clicking in the preview window outside all frames triggers the update).
Something similar happens in SF-HDR; when switching between files the NegaFix-histograms are not updated immediately (in this case switching from expansion to levels and back triggers the update).