SOT: Scanning old computer docs

Hi Kevin, Are you _sure_ the two modes use the same optical sensor? Often sheet feed systems use a different sensor somewhere along the paper path. I suspect they are not, given the odd colour pattering off the top edge of the paper, on the autofeed image. If those two images are definitely produced by the same sensor, through the same glass, then there are a few other possibilities: * A 'mode settings' problem. Scanners always have a bunch of modes, such as photo vs printed, sensitivity adjustment curve, gamma correction, etc. It may be your machine uses different settings for flatbed vs page feeder, and the page feeder settings are _way_off_. * Keeping the paper flat on the glass. Someone else pointed this out - maybe the sheet feed process uses rollers and the paper is bowing away from the glass in those two really bad wide streaks. But there are other problems too, because there are fine streaks as well. * Another thing scanners do, is calibrate the sensor using a standard white/black image bar, usually behind one end of the flatbed bezel. The sensor always has imperfections, but subtracting the observed calibration data results in a clean image. (Ideally, sometimes not.) Maybe your machine uses separate calibration datasets in the two modes, and the one for autofeed is rooted. Download a manual and read. There are defects in your 'good' flatbed image too - for eg the bleed-through of the orange lettering on the other side of the sheet. The way to correct that is to use a black, highly light absorbent backing sheet. Eg black velvet. But you probably can't do that on your scanner. This defect is typical of scans done by people with little discernment for image quality. They don't even notice. Then there are fundamental defects common to both images: * You've used PDF as the end format. As a result the image is stored in lossy JPG coding, and thus has typical JPG edge noise. PDF does not allow any sensible image coding scheme such as PNG. Just a few old ones: JPG (OK for photos, but awful for any image with fine detail and hard edges), TIFF (lossless but very inefficient), the horrible 'Fax mode' (B&W, in which the captured data is stored losslessly, but the capture process is horrifically lossy and destructive of image quality.) Plus another abortion called JBIG2. ( A patch tokenization scheme that is so bad it should be illegal.) * The originals are screened printing, where all tones are created by varying the size of saturated YMCB ink dots laid in a regular grid. To scan this kind of document adequately, you HAVE to scan at high enough resolution to resolve the edges of the tiny dots (the only way to avoid obnoxious moire patterning), then post-process the image to convert (blur) the screen grid dots to smooth colour shading (still at very high resolution) then scale the image to a desired final size. Then lastly change the image encoding to a suitable (lossless) form (eg one of the PNG modes) for sane file size. This is still unavoidably a manual page-by-page process if you want archival quality. And PDF flatly doesn't allow it. Once you realize this is so, you'll become very depressed about all the people who think they are 'saving worthy documents for posterity' by scanning them into PDF. Your images still contain remnants of the screening dots pattern, but messed up by JPG artefacting. Thus the file size is stupidly high due to all the superfluous and messy fine detail. Zoom right in to see it. Sorry to not be very helpfull, Guy At 11:56 AM 3/04/2021 +1100, you wrote: