Adjust PDF Contrast with Adobe Reader/Acrobat?

Question

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 **

Answer 1

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.

Answer 2

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

http://www.imagemagick.org

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

More info and examples on the site.

Answer 3

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

Answer 4

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 STDU Viewer: This is no longer actively maintained; with the last update being in or before 2015.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 .

Answer 5

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.

Answer 6

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.

Answer 7

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

Answer 8

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.

Answer 9

I support a fast Multi Format viewer that can adjust colours of scanned page PDF.

HOWEVER it cannot alter the contrast of such contents, so it cannot increase "brightness" of dull scans, as then they would be outside of the PDFs internal colour range.

Such images need to be altered in pixel editors and one that views and resaves PDF is IrfanView where you can visually see the changes and then save a profile for running on batches of files.

Answer 10

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.

Answer 11

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:

• Open Paper port, navigate to the PDF
• Right click the PDF within PaperPort
• "SET Tools"
• Auto-enhance (or Apply current white/black points)

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

• Open Paper port, navigate to the PDF
• Right click the PDF within PaperPort
• Open with ImageView
• In the top ribbon, pick "White point" and now click some area of the scanned page you think should be white (eg: grey background of a low contrast scan).
• In the top ribbon, pick "Black point" and now click some area of the scanned page you think should be black (eg: The grey text letters of a low contrast scan)

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)

Answer 12

I've run into this as well. for some reason version 5 of the reader seems to work as expected. I think it might be something in the creation, but I've not tracked it down yet.

Answer 13

What I did was change the color of the text by going to edit menu, clicking on preferences and then the accessibility tab. You can customize the color for the document text. It doesn't do anything for the images, but at least you can see the text on a dark background.