Adjust PDF Contrast with Adobe Reader/Acrobat?

We get PDF's from our professor to read for homework but they're often scanned documents, is there a way to adjust the contrast of the text to make it easier to read? Edit: I've got Photoshop but is there a way to do it from a PDF reader? Edit2: Windows XP, 7 ** Windows or Ubuntu Only **

asked Mar 8, 2010 at 16:21 7,194 14 14 gold badges 43 43 silver badges 52 52 bronze badges

I'd suggest asking your professor to scan it as black & white instead of grayscale or 24-bit color, as long as the content is mostly text and line art (i.e., no photos or gradients). Not only will this make the documents perfectly legible, but it will also shrink the file size dramatically. Maybe you can turn this to your advantage and get some extra credit in return for rescanning or fixing the contrast on all the PDFs.

Commented Mar 8, 2010 at 19:04 Commented Feb 14, 2016 at 23:38 Commented Apr 10 at 22:00

13 Answers 13

You can try this:

Go to Edit>Preferences>Accessibility

This will not change the true contrast, but you can pick contrasting colors of your choice, or one of the defaults, as in the screenshot.

answered Aug 3, 2011 at 21:23 25.5k 6 6 gold badges 49 49 silver badges 72 72 bronze badges

I have tried this but it doesn't work. I think this works only for ebooks. My pdf is scanned text, so it's made of images. When do accessibility thing, the whole page goes white. It doesn't recognize the text.

Commented Aug 5, 2011 at 5:09

I see. If it is a scanned image, I do not think there will be much you can do. I would mention it to the professor so he can consider adding contrast before he makes it a PDF.

Commented Aug 5, 2011 at 5:15 Worked great for me though, so still a +1 Commented Aug 19, 2011 at 20:07

I set grey letters over black background using this method. When I scroll down I get horizontal white stripes. Very annoying. Any idea how to solve it?

Commented Jul 5, 2018 at 9:24

You could try Imagemagick - it's a graphics manipulation program that can read and write PDFs too.

There are a few command line options that may help - for example: -normalize, -contrast and -contrast-stretch

Try something like: convert original.pdf -contrast new.pdf

More info and examples on the site.

312 2 2 silver badges 16 16 bronze badges answered Aug 3, 2011 at 21:24 Linker3000 Linker3000 27.9k 3 3 gold badges 53 53 silver badges 74 74 bronze badges

Good answer, and one that works fine; but note that ImageMagick doesn't do the PDF interpretation on its own -- in the background it employs Ghostscript as its delegate doing some of the hard work.

Commented Aug 8, 2011 at 19:38

could not get this trick to work -- looks like ghostscript errored out (screenful of mostly incomprehensible text, but near the end: "postscript delegate failed 'thefilename.pdf' No such file or directory (but it's there)

Commented Mar 27, 2014 at 14:11

On windows, downloading and installing 32 bit ghostscript got it working for me. ghostscript.com/download/gsdnld.html

Commented Apr 11, 2017 at 9:00

on windows using imagemagick 7.1.1 this worked well magick template.pdf -alpha off -threshold 80% temnew.pdf adjust the % to suit your sit, at 50% mine produced a blank page

Commented Mar 18 at 7:36

Under OS X, you can use ColorSync which is installed by default. There are many filters, and one is for decreasing contrast.

231k 71 71 gold badges 622 622 silver badges 603 603 bronze badges answered Nov 8, 2010 at 9:49 49 2 2 bronze badges

This is a useful workaround though users should beware that it will likely make the size of the PDF much more hefty. I was able to salvage a barely readable 11 page scan but the file went from 6.6 mb to 17.7 mb.

Commented Feb 6, 2019 at 19:25

I've voted this up sometime in the past so I believe this worked at some point, but now I can't figure out how to use it (on macOS 10.15 Catalina)… does it still work?

Commented Oct 12, 2020 at 9:21

I've found two PDF readers that allow you to change brightness, contrast and gamma for PDFs from scans:

  1. YACReader: It is actively maintained, but is specialized for comic book formats. It does display PDF files, but seems to lack such staple PDF viewing abilities as selecting and copying text, and a continuous view. It is available as an x64 windows prog. that runs on Win7. To change the contrast, brightness and gamma of a document you are viewing, click the Options gear on the toolbar on the upper right, and choose the Image Adjustment tab. It supports a wide variety of formats; and has a lot of ability to rotate the view as well.
  2. STDU Viewer: This is no longer actively maintained; with the last update being in or before 2015. It has the ability to select and copy text, as well as do a continuous view. In fact, it defaults to page width, continuous view; as all PDF readers and PDFs in general always should. It is available only as x86, but still works great under Win7 x64. To change the contrast, brightness and gamma of a document you are viewing, go to View | Settings. It also supports a rich variety of formats, even comic ones, can rotate pages, and has a rich set of navigation tabs .
answered Dec 31, 2020 at 13:54 CodeLurker CodeLurker 234 2 2 silver badges 4 4 bronze badges

Thanks! I used STDU viewer to view then export to a new a high-contrast PDF. It did a great job (even though running under the latest Win10).

Commented Oct 29, 2021 at 17:38

I saved it as a Microsoft Word file in Acrobat Reader. Then I opened the Word Document and adjusted the brightness and contrast of the image until it was readable. It makes for an expensive print, but it works.

answered Nov 7, 2010 at 14:45 11 1 1 bronze badge

If you open it in Photoshop and resave as a PSD file you can or if you want to apply on all pages, do the following:

  1. Open the pdf in Preview.
  2. Make sure the preview pages are showing
  3. Click page one
  4. "Select All" (or Command + A), All pages are selected
  5. Run any Preview tool/filter and all pages will be affected simultaneously

If your pdf is locked, you will not be able to perform this operation.

answered Mar 8, 2010 at 16:35 5,765 10 10 gold badges 44 44 silver badges 66 66 bronze badges

I don't want to sound negative, but he does state he would like to do it with a PDF reader ;-) Photoshop is a quite expensive PDF reader!

Commented Mar 8, 2010 at 18:02

I know. it is :) but the feature requested is not in new version unfortunately. Hope my answer will help him since he has Photoshop.

Commented Mar 8, 2010 at 18:27

I used to use Photoshop to try to fill out forms before I learned of other options, regardless, my experience with photoshop and pdf makes me fear ever doing that again. Thank tho.

Commented May 14, 2010 at 21:50

I changed contrast with PDFClerk. It has a lot of filters in there, when exporting PDF.

answered May 13, 2010 at 0:20 3,307 4 4 gold badges 27 27 silver badges 33 33 bronze badges Thanks but I should have mentioned this is for a Windows machine. Commented May 14, 2010 at 21:47

You can use the graphics card or monitor settings to handle this.

See this post as well.

For that you could use a system wide gamma/brightness/contrast setting; usually if you have a modestly advanced graphics card, its control panel will have options to change gamma / contrast / brightness / hue. e.g. NVIDIA control panel, ATI Catalyst Control Center/Panel etc. It will affect the the whole system, but you can always change it back when you're done viewing the file.

answered Aug 3, 2011 at 21:10 Mehper C. Palavuzlar Mehper C. Palavuzlar 55.6k 50 50 gold badges 195 195 silver badges 254 254 bronze badges

You can also try Nuance Paperport (I got this "free") with my Brother MFC scanner/printer.

Essentially if you have a dark grey font on a light grey background (a low contrast scan), then you tell it to "stretch" the dark grey to black and the light grey to white. This is done by setting the black/white points as follows:

Now you can manually set the while/black points for finer control

I used this to create a legible black and white PDF from a scan that was originally black text on dark blue paper (that scans as a very low contrast)

answered Aug 19, 2013 at 18:18 DeepSpace101 DeepSpace101 8,857 12 12 gold badges 46 46 silver badges 47 47 bronze badges

Adobe Reader does not seem to have this option, unfortunately. It can change the colour of text (under the Accessibility preferences), as other answers have mentioned, but not the contrast of scanned images.

However image contrast can be adjusted quite accurately with the free, ad-supported version of PhotoPea, which is a Photoshop clone. It runs in your browser, so no installation is necessary.

Here are the steps:

  1. Open photopea.com in your browser
  2. Drag your PDF file into the main window. It should open up and show all pages from the PDF.
  3. Expand the layers inside "Page 1", "Page 2", etc. and select the "Bitmap" layer.
    You can use Ctrl + Click to select multiple bitmap layers and adjust multiple pages at once.
  4. Press Ctrl + L or choose Image > Adjustments > Levels from the menu, and drag the sliders to adjust the black, white and mid points to your preference.
  5. You can now export to PDF (or any of the other file formats) via File > Export As. > PDF

I have no affiliation with Photopea, but have found it a very useful tool over the years.

UPDATE: I think PhotoPea currently has a bug whereby some image resolution may be lost when opening raster PDF files. If this is an issue for you, please take note. Hopefully this gets fixed.