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Old 08-04-2017, 06:08 PM   #3
j.p.s
Wizard
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Join Date: Apr 2011
Device: pb360
larger images

TL;DR : I'm attaching sets of larger images for the line drawings and tables for this book.

Many people with high resolution ereaders suffer from tiny illustrations when reading books with images designed for readers with 6" 800x600 screens. This is happening for me with 'A Thousand Miles Up the Nile'. I've discovered that the Internet Archive has a PDF of this book made from 1731x2755 pixel scans (about 300dpi) at https://archive.org/details/thousandmilesupn00amel

I've made various resolutions of the line drawings and tabular text figures and attached them here. There should be a set of images near optimum size for just about any reader. Just substitute for the image of the same name in HarryT's EPUB above. Each set has been scaled by a fixed factor applied to the full size scanned images.

archive.org also have a tar file of the individual JPEG2000 scans and a zip of the individual JPEG2000 pages extracted from the from the scans in the above tar file which have margins far outside the physical page.

The PDF pages are each a combination of 2 PBM files and a PGM file. One of the PBM files is a mask, which allows the part of the PDF page with no "ink" to be completely white. I used the command line utility pdfimages to extract only the pages with tables and line drawings. I next used the ImageMagick command line utility convert to crop the corresponding JPEG2000 image of the page with the line drawing or table. The file numbers for the JPEG2000 images are 30 greater than the book page number and the PDF page numbers are 2 less than the JPEG2000 file number.

I wrote a Perl Data Language script to unzip only the JPEG2000 files I needed that I needed, crop and mask the PDF images, do some contrast stretching, and convert to PNG. I then used the netpbm utility pnmscale to reduce the images by various factors, then cjpeg to convert to jpg. I've used jpg instead of PNG, because most og the 8 bit PNGs were only a little smaller than the jpg and a couple of them were much larger. Except for those two, 4 bit PNGs would be much smaller and would be ideal for e-ink since e-ink only has 16 gray levels. But almost all e-ink devices do not display 4 bit PNG images correctly, which bitterly disappoints me. jpg also has the advantage of not needing to edit the content.opf or html image references. I also did some minor cleanup and touchup with GIMP.

I'm including the script and the PNGs in in the zip of the full size images since it documents the details of figure numbers, page numbers, crop size and location, and command options. (Almost everything probably could have been done with ImageMagick but that was too tedius and awkward for me to even contemplate.)

The widest full size image is 1536 pixels and the tallest 1986 pixels. Use that to decide the reduction factor needed for your device. Many of the tables are much narrower than the page. I recommend using tables from the least reduction that will still fit. Mix and match size to taste can also be done for the other images as well.

To use the larger images, just unzip HarryT's epub into a empty directory and copy the larger images you want over the ones in the iamges directory of the same name. rezip the epub, put it on your device, and enjoy the larger images.

Rezip example assuming you are in the unzipped directory and using half scale:

zip -0Xq ../AThousandMilesUptheNile0.50x.epub mimetype
zip -r9Dq ../AThousandMilesUptheNile0.50x.epub *
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Attached Files
File Type: zip tmun1.00x.zip (4.72 MB, 128 views)
File Type: zip tmun0.75x.zip (1.14 MB, 122 views)
File Type: zip tmun0.60x.zip (866.0 KB, 117 views)
File Type: zip tmun0.50x.zip (701.7 KB, 126 views)
File Type: zip tmun0.40x.zip (499.2 KB, 120 views)
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