invert pdf colors

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invert pdf colors

Postby tsttm » 18 Jun 2009, 12:34

hey guys,

new to the forums, i think it's a great idea as it's getting hard to sort through all the great ideas & comments on the instructables page.

i'd like to be able to invert the colors of pdfs..i find i prefer to read with light text on black. I know adobe reader has a 'high contrast' option...the problem with that is it doesn't work with all pdfs, but also because it doesn't actually edit the pdf itself..so if i open the pdf in 'pdf annotator', the pdf is back to black on white.

I haven't come across a specific program that does this. But, starting from a pdf, it seems the simple solution is to use a program to convert it to an image files, then batch edit the images to create 'negatives' & then convert back from image to pdf. (of course, if scanning your own..then you're already at the image step).

The reason i pose this question here is, I'd like to hear people's opinions on which software would work (preferably free). I did manage to do this using PDFill to convert from pdf to image & then 'fastone photo resizer' to batch edit the images & then PDFill to convert back to pdf. However, this only worked once. I've had trouble getting PDFill to convert other pdf files i have (often it'll only convert the first page to an image).

The other reason i pose it here is, i understand the page builder software is made by the people involved with this DIY (right?). I know nothing about programming, but I wonder if it's possible to add a feature that will also batch process your images into a negative (white text on black) as an option during the post editing steps.

thanks very much!
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Re: invert pdf colors

Postby spamsickle » 18 Jun 2009, 12:55

ImageMagick (the free open-source application I'm currently using to crop and rotate my JPGs and convert them to PDFs, though I may soon be using FineReader or Rob's software) will do this easily:

convert page1.jpg -negate npage1.jpg

If you're planning to do OCR, you may want to do that first; I'm not sure how well any of those apps handle white text on a black background.

The good thing about ImageMagick is that it's a command-line application, which means I can easily create a script to convert hundreds of pages without all the hands-on point-and-click nonsense that GUI software imposes.
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Re: invert pdf colors

Postby tsttm » 18 Jun 2009, 15:44

Thanks. I will check this out.

I do eventually want to do OCR on my pdfs and/or scans. While i don't know much about OCR or ebook readers yet..i presume once OCR is done, there are probably other options for reading in inverse colors using ebook reader software instead than reading in pdf i suppose?
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Re: invert pdf colors

Postby daniel_reetz » 18 Jun 2009, 15:53

it would be very interesting to see a kind of "quick start guide" for imagemagick with book scanning in mind...
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Re: invert pdf colors

Postby Karyudo » 18 Jun 2009, 16:17

tsttm wrote:[T]here are probably other options for reading in inverse colors using ebook reader software instead than reading in pdf i suppose?


I use Stanza on my iPod Touch to read books from various text formats, and it lets me quickly switch to using inverse colours. This is but one data point, but I'm thinking that if free software on a platform not really designed for reading text has this functionality, then it's probably reasonable to think other dedicated e-book readers will have it, too.
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Re: invert pdf colors

Postby daniel_reetz » 20 Jun 2009, 13:27

I also like to read in negative, but I have no idea why. Anyone care to speculate?
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Re: invert pdf colors

Postby Karyudo » 20 Jun 2009, 20:28

Some data I saw indicated the best native? inherent? contrast ratio for text is white on blue (just like Paperclip for the Commodore 64, and later WordPerfect...), and second best is black on white. With white on black not far behind. So maybe that figures in?
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Re: invert pdf colors

Postby JotaPe » 21 Jun 2009, 16:49

For transform to negative images, try virtualPhotographer and virtualStudio (http://www.optikvervelabs.com/virtualstudio.asp): free, standalone app. or Photo***p pluguin)

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Re: invert pdf colors

Postby tsttm » 29 Aug 2009, 12:40

just wanted to add some comments now that I've tried a few trings and have started doing my own scanning.

first, I've found that foxit seems to do a better job at replacing colors (if selected) vs adobe reader. I've opened files in adobe that will not display at all only to open it in foxit & have it replaced the colors perfectly.

second, now that i've started scanning. I've found that running the images through fastone photo resizer for batch rotation & photo negative has been quite good. Fastone has a number of other batch operation options as well. I do play with the contrast & brightness as a straight up negative usually comes out as white text on grey background. By adjusting the brightness/contrast, I can get the background close to black.

Here's a sample of my color inversion using fastone:

Image

I think there's some improvements to be had in terms of crsipness of the text..but i think that's a matter of playing with the focus/aperture/speed...i'm not sure i've found the optimal combination yet. Fastone does have a sharpen option, & in this example, i used +1 for sharpen.

Finally, just a note- i've found abbyy finereader doesn't seem to OCR as well with inverted color files (even when using its own color inversion option- which only makes the background grey..not black). So, i tend to use the non-negative images if i want to do OCR (for now). Perhaps a bit more testing will reveal that abby works fine with certain inverted color settings.
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Re: invert pdf colors

Postby tsttm » 29 Aug 2009, 12:43

also, with a negative, some artifacts or imperfections may appear more evident. (for ex. it's obvious in my example that my light source is not evenly distributed as it's black in the middle & greyish toward the edges). however, i still prefer white text on black, so it doesn't bother me too much.
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