#98 Brightness and contrast adjustment for black and white text scans

[Luke]

Is it possible for NAPS2 to adjust brightness and contrast of black and white scans like scanner TWAIN drivers do during preview scans?

When I use TWAIN to do a Scan Preview and I lower the brightness (contrast is disabled) to darken the text only the actual printed text on the page is darkened. The white background is not darkened. However, when I use NAPS2 to do the same adjustment the entire image, background and all, is darkened. See attachments for illustration.

I opened this ticket as a request for support instead of a bug fix because I do not believe this to be a bug. My guess is that the TWAIN driver generates layered data during the preview scan and therefore is able to distinguish between foreground and background, but when NAPS2 gets the image from the TWAIN driver it's been flattened into a single layer. At that point NAPS2 can no longer distinguish between foreground and background.

I have a feeling that the answer to my original question is going to be "no", but I'd like to get that answer from the developer community rather than my own assumptions.

Attachments

• twain.1.png, screen capture of an HP 8600 TWAIN Preview scan before adjustment
• twain.2.png, screen capture of an HP 8600 TWAIN Preview scan after adjustment
• page.1.png, original scan of a document with no adjustment
• page.2.png, original darkened 70% in TWAIN Preview scan
• page.3.png, original darkend 70% (-700) using NAPS2 image adjustment

[Luke]

I'm referring to using the toolbar brightness/contrast after scanning. I exclusively use the native TWAIN driver interface for scanning; I do not specify scan properties in NAPS2 profiles.

The vast majority of scan acquisitions that I do are black and white with text intent at 200 or 300dpi resolution. I noticed that preview scans are acquired in color first (they momentarily appear in color) and then converted (thresholded) to black and white. My guess is that the driver is working with the original color acquisition and the brightness bar is repurposed to adjust threshold instead of brightness. HP probably decided against making a separate slider bar called "Threshold" because only a small minority of users would understand the difference between the two. I didn't understand what thresholding meant until I looked it up.

As I understand it, if I acquire (scan) an document in black and white, NAPS2 would not be able to threshold the image anymore (please correct me if that's incorrect). Since that's how I acquire the vast majority of my scans I'm not sure that I would find that feature useful, but I suppose that it could come in handy if I needed to convert an existing color image (i.e. a saved color scan of a document that I made days/weeks earlier and no longer have the original paper) to black and white.

I'm not sure that I want to change habits to scan in color and the convert/threshold individual pages to black and white in NAPS2. I'll probably forget to take the extra step and start saving lots of scans in full color instead of black and white. I'll most likely continue to select black and white and use the TWAIN preview scan interface to adjust threshold as needed.

The feature that you proposed sounds like an interesting "nice-to-have", but I think that the preview scan facilities in the TWAIN driver would better serve my purposes. Thank you very much for offering to build it, though.

If you still feel like making it, please don't let me sway you from doing so. Also If my understanding of how brightness/contrast/threshold adjustments work is not correct, please let me know.

Thanks again for your contributions to this fantastic product. Merry Christmas!

[Luke]

You can close this ticket. My questions have all been answered. Thanks.