Update to Epson scanning article: how to bypass all tonal adjustments

[Ken Lee]

What your probably seeing there is vuescan simulating the exposure change, that it intends to make when you actually do the scan. Vuescan actually allows you manual control this, and I think it also allows you do this for each color channel. It certainly allows the adjustment of the later. Just like changing the shutter speed, changing the exposure time of the CCD is not a tonal change.

There is no manual control of this in Epson scan, though presumably it makes use of this feature, most probably it has calculated it before you are presented with the preview.

I think I finally grasp what you are saying. Duhhh

I made a scan with VueScan and configured it to output both a raw file and a tiff file. The tonal scale of the tiff file was affected by cropping and adjustments made in the Color tab like curve low, curve high. In addition, a gamma adjustment of approximately 2.2 has been applied to the tiff file. The resulting tiff file matches what we see in the preview pane.

The raw file, on the other hand, looks rather dark, because not even a gamma correction has been applied. It's just the original scanner acquisition of the image.



If we apply a gamma correction to the raw file, it begins to resemble the TIFF image (which may also contain tweaks from the Color tab and cropping).



Finally, the Epson scan, Apple Image Capture and Windows Scan drivers are all silently applying a gamma correction to the scan. Turning off all corrections in the Epson drivers, we get an image which matches Apple Image Capture and Windows Scan, but none of these 3 approaches actually delivers the original scanner capture because a gamma adjustment has been applied in all 3 cases. In fact, the only configuration which delivers the original scanner capture, is the VueScan raw file.

...Is this correct ?