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| Anybody wants old data books (UK)? |
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| PlainName:
For anyone thinking of acquiring a large format ereader for datasheets and/or notes, this channel is well worth spending a few hours perusing: https://www.youtube.com/c/MyDeepGuide/videos He puts pretty much all of them through their paces, uses them for real and gets into the stuff magazine reviews wouldn't think of (like how the nib-on-screen feels compared to actual paper). |
| tom66:
On JPEG in PDF, it is possible to set the quality at near lossless (this is generally agreed as Q=96..99) where file sizes are large but image compression still occurs. Note that most JPEG codecs divide the terms from DCT determined by the Q factor. Very high Q factors leave most of the DCT components left (few components rounded towards zero), so you are only left with the artefact of DCT, which can be very good for the right JPEG encoder. You can compare a JPEG image compressed with a modern libjpeg codec at Q=96 and tell me you can distinguish the difference: certainly, it is not possible without looking closely at the pixel level. Yet file size will be 1/4 or less of BMP. PNG is not a good codec for compressing anything scanned due to variation in the page brightness or fixed pattern noise on the sensor. It will not work well with such documents and I would be surprised if it offers much over BMP. |
| TerraHertz:
--- Quote from: tom66 on April 27, 2022, 08:20:59 pm ---On JPEG in PDF, it is possible to set the quality at near lossless (this is generally agreed as Q=96..99) where file sizes are large but image compression still occurs. Note that most JPEG codecs divide the terms from DCT determined by the Q factor. Very high Q factors leave most of the DCT components left (few components rounded towards zero), so you are only left with the artefact of DCT, which can be very good for the right JPEG encoder. You can compare a JPEG image compressed with a modern libjpeg codec at Q=96 and tell me you can distinguish the difference: certainly, it is not possible without looking closely at the pixel level. Yet file size will be 1/4 or less of BMP. PNG is not a good codec for compressing anything scanned due to variation in the page brightness or fixed pattern noise on the sensor. It will not work well with such documents and I would be surprised if it offers much over BMP. --- End quote --- It's funny you are so conversant with codecs, but so basic on scanning. The trick with scanning documents (text, diagrams) is to pick levels and post processing, so that 'white' areas are really all white, and 'black' is really all black, leaving only edges to be maintained with minimal gray-levels. PNG works brilliantly with such. 4 bits per pixel for edge shading, and all blank areas vanishing into the run-length compression. PNG still isn't ideal for documents, but it vastly beats other contenders. And if you're comparing something to BMP, then you should know you're wasting your time. |
| tggzzz:
I scanned a 48 page scope service manual into a <8MB pdf file. It included photos, text, schematics, colour PCB layouts. That's too large to be attached here, but I've attached a similar one below. In my opinion it is just a legible as the original, unlike many you find in the repositories :( The basic workflow is dictated by what I found on a bog-standard linux box. No doubt there are better dedicated tools, but... The steps were: * scan at 300dpi, save as colour JPG file * use a shellscript to convert each page to two small TIFF files, one more suitable for photos, one for text/diagrams * for photos, optionally posterise it to reduce size * convert each TIFF file to a single-page PDF * concatenate all the PDF files to produce the single final file I previously tried simply including JPGs in a PDF file, but my tools compressed them so much they were unacceptable. Using TIFF files avoided that. |
| nctnico:
--- Quote from: TerraHertz on April 28, 2022, 03:30:36 pm --- --- Quote from: tom66 on April 27, 2022, 08:20:59 pm ---On JPEG in PDF, it is possible to set the quality at near lossless (this is generally agreed as Q=96..99) where file sizes are large but image compression still occurs. Note that most JPEG codecs divide the terms from DCT determined by the Q factor. Very high Q factors leave most of the DCT components left (few components rounded towards zero), so you are only left with the artefact of DCT, which can be very good for the right JPEG encoder. You can compare a JPEG image compressed with a modern libjpeg codec at Q=96 and tell me you can distinguish the difference: certainly, it is not possible without looking closely at the pixel level. Yet file size will be 1/4 or less of BMP. PNG is not a good codec for compressing anything scanned due to variation in the page brightness or fixed pattern noise on the sensor. It will not work well with such documents and I would be surprised if it offers much over BMP. --- End quote --- It's funny you are so conversant with codecs, but so basic on scanning. The trick with scanning documents (text, diagrams) is to pick levels and post processing, so that 'white' areas are really all white, and 'black' is really all black, leaving only edges to be maintained with minimal gray-levels. PNG works brilliantly with such. 4 bits per pixel for edge shading, and all blank areas vanishing into the run-length compression. PNG still isn't ideal for documents, but it vastly beats other contenders. And if you're comparing something to BMP, then you should know you're wasting your time. --- End quote --- Still I recon that original (color!) scans with 600dpi or better resolution would be most ideal (in PNG format for example) because you can always post-process these to improve quality once newer technology to deal with digitising paper records comes along. Storage is super cheap nowadays anyway. Epub (which supports PNG natively) could be a good alternative to PDF as a distribution format. BTW: choosing a single level between black/white doesn't sound like a good solution. AFAIK there are better ways available nowadays that use a dynamic threshold to determine which parts are black / white. |
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