How to make a transparent background in PDF. Adding a background to PDF documents. Edit with us - it's safe

A background is a color fill or image that appears behind the content of a document. The PDF format allows only one background per page. You can set a unique background on each document page.
For the background, you can select an image from a file, adjust the color, location on the page, specify the page numbers on which it will be displayed, and also save the settings necessary for further use.

Adding a background to an open document.

To add a background to a PDF document, select from the menu: Document>Background>Add.

• Source document Selecting the type of background to be inserted. This can be a color fill or an image from PDF file A.
  Color When the marker is installed, the background of the document page will be filled with some color. Select a background color from the list.
  File When the marker is installed, the source material for the background will be the image loaded from the PDF file.
  Review- Select the original PDF file for the background.
  Page number- Number of the file page whose image will be used as the background. (The total number of pages of the file is displayed under Total Pages)
  Scale- The scale of the background in relation to the original image inserted from the PDF file. To make this item active, remove the marker in the item View > .

• Saved settings List of saved background templates.
  To add a template, specify the required backgrounds and click Save. In the dialog box that appears, write down the name of the template.
  To delete a template, select it from the list of saved settings. In the dialog box that appears, confirm deleting the template.

• View Setting the parameters of the inserted image.
  Turn- The value of the rotation angle (in degrees) of the background in relation to the document page.
  Opacity- Opacity value (in percent).
  Scale relative to landing page- The scale of the background in relation to the document page on which the background will be added.

• Position Configuring settings for the location of the watermark on the document page.
  Vertical shift- Value for shifting the background vertically relative to the selected position: Top, Center or Bottom.
  Horizontal shift- Value for shifting the background vertically relative to the selected position: Top, Center or Bottom.

• Units- Select units of measurement to specify shift distance.

• Page range Select a range of document pages to add a background to.

Removing the background from a document.

To remove the background, select from the menu Document>Background>Delete. The background will be removed from all pages of the document.

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2

There is no way to do this directly without using a free one software or a free tool that I know of. (Because in general, you will have to change All colors in the PDF pages, not just the background alone, so you may have some contrast and color differences.)

What did you describe for Adobe Reader doesn't change the PDF file itself, it changes the way the pages are displayed (by inverting colors or similar). The PDF remains unchanged during and after viewing.

However Maybe be able to achieve the same by applying suitable color profile ICC for PDF input and produce using (very late) Ghostscript, new PDF output from this,

the question remains: what IS "suitable" ICC Color Profile for your purpose??

I briefly looked at applying a grey-ish background to a PDF using the pdftk ... background ... command line. But this will probably make some or many PDFs unreadable. (A black the background will definitely make it unreadable, because most of the text is black and will stay that way.)

To create a PDF page (A4 format) that could serve as a gray background, you can use Ghostscript: gs -o gray.pdf -sDEVICE=pdfwrite -g5950x8420 -c ".8 setgray 0 0 595 842 rectfill showpage" .

Then apply it to the original PDF (A4): pdftk original.pdf background gray.pdf output orig-with-backgr.pdf .

Please note that this will only change the background of those pages (or those areas of the pages) where the original background is transparent. like most text based PDF files are. It will be Not work for pages or areas where the background is opaque white or colored.)

You can also achieve permanent color changes (reverse colors) quite easily using ImageMagick. But this will at the same time chew and mince your nice vector PDFs by converting them to full bitmap pages: convert nice.pdf -alpha off -invert inverted-colors-ugly-raster.pdf .

Finally, here's a rather unreliable way to do color inversion using Ghostscript. It sets colortransfer function for the output PDF file:

Gs -o output.pdf \ -sDEVICE=pdfwrite \ -c "(1 exch sub)(1 exch sub)(1 exch sub)(1 exch sub) setcolortransfer" \ -f input.pdf

It's unreliable because not every PDF viewer will appreciate that setup. I've tested this several times in the past...

These spectators DO NOT SHOW inverted colors:

1. Adobe Reader
2. Adobe Acrobat
3. Ghostscript/gs
4. Chrome's built-in PDF renderer ( "pdfium")

These are the ones DO NOT SHOW inverted colors:

1. Chrome with pdf.js
2. Firefox with pdf.js
3. Zathura
4. MuPDF

0

In addition to your answer, there are probably tools like PitStop or pdfToolbox (affiliation warning) that can apply such a transfer curve once it is there (in other words, calculate new colors given the transfer curve). This would make it permanent and therefore accessible to all viewers :) - David van Driessche Apr 29 15 2015-04-29 22:20:55

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@DavidvanDriessche: Thanks David, of course I *meant I didn't know about any "Free" (as in freedom) or "free" (as in gratuitous), I know...I completely forgot mention commercial utilities, although I intended to when I wrote my answer. - Kurt Pfeifle Apr 29 15 2015-04-29 22:29:25

3

Just in case OP doesn't really need to change the color of a PDF document constantly but only wants PDF viewer except Acrobat, which can also change the displayed colors...

MuPDF: MuPDF is a lightweight PDF viewer (among other things). It can invert the displayed colors with a simple i stroke for any document while it is open. MuPDF is also available for Windows (and iOS, and Android, and OSX, and Linux). (This is made by the same company that brought us Ghostscript).

MuPDF screenshots here: "normal" view (left) and "inverted" view (right)

SumatraPDF: It is a very popular PDF viewing alternative for Windows. Its PDF rendering engine is based on MuPDF. Hit. in presentation mode, it changes the background to black. Pressing w in presentation mode, it changes the background to white. (I don't think he can either invert all colors, but I don't have them latest version, available right now, to check out.) To run with -invert-colors added to the command line, it inverts the colors for the rendered document.

Zathura: A lightweight PDF viewer for Linux and OSX that can be controlled using Vim keyboard shortcuts. ctrl + r will recolor the visualization of any open document. The background will change to dark, the texts will change to bright gray (however it will not invert a, such as blue text to yellow, like MuPDF does). I'm not sure if it's available on Windows either.

Evince: Gnome PDF viewer is available for Linux, OSX and Windows. It can also invert the colors of an open document; Key combination: ctrl + i.

XPDF: XPDF is a fairly ancient PDF viewer for Unix + Linux (not sure if there is one Windows version, perhaps in Cygwin). It has a launch option in command line: xpdf -rv -papercolor "#333333" file.pdf inverts colors (-rv for reverse video , -papercolor allows you to change the background to something other than pure black [as any inverted white will become]).

2

As you asked for an API, I'll add one more feature into the mix. It's actually possible to write a plugin for Adobe Acrobat (possibly for Adobe Reader too, but Reader plugins are more complex) that interferes with the display.

A long time ago I wrote code for Enfocus PitStop to implement a wireframe rendering mode for PDF files inside Adobe Acrobat. Press the button and the display changes to a wireframe, press again and you have the normal view. This works because you can (as a plugin) modify the display list (list of objects) drawn with Acrobat.

This means that to draw your custom display mode you can create new list display (or change the existing one) so that it has a rectangle at the very back of the color you want, and then change the color of all the objects in the display list to suit your needs.

This is relatively tricky as it makes it more complex: if you don't want your changes to affect the PDF file on disk, you have to catch a lot of Acrobat notifications and revert your changes. For example, if a user tries to save a PDF document while viewing in your display mode, you should make sure that you are warned about this and undo the changes at the time of saving. Adobe Acrobat makes this possible because it sends you notifications before and after the saving process, but it's still a lot of work to make sure nothing gets screwed up.

But this is a completely healthy and very flexible way to implement what came after. Just make sure you have more than a couple of weeks to implement it :)

How to get rid of the gray background?

Master's answer:

Often, when you scan a particular document, the background of the image turns out to be gray. Recognizing and working with documents in general is becoming more difficult. There are several methods for cleaning such documents in pdf and djvu formats.

Required: ScanKromsator program.

ScanCromator is used to remove the gray background from the resulting scans. You can download this program from the official website of the program developers at djvu-soft.narod.ru/soft/#scan. Select the appropriate version of the application. Click on the “Download” link.

Install the application on your computer. To remove the gray background from a pdf and djvu file, open it in ScanKromsator. Go to the application settings, check the Enhance image option, click on the “Gray enhance” button, instead of which you can also use hotkey IN.

In the Background cleaner tab, set the background cleaning settings. To do this, set the Cleaner passes parameter to equal to one. This will remove the background from the scan. If there is very little contrast between the color of the text and the photo in the document, then the checkbox should be checked for the Correct low contrast parameter, which will allow you to adjust the recognition sensitivity text information on a gray background.

Start with a value of 20-25, gradually decreasing it by 5. After ScanCromator removes the background of the scanned image, it will also check the file for the presence of text, the contrast of which relative to the background color is equal to the specified sensitivity threshold or greater. And if the specified value is found, then the color of such a point will either not be changed at all, or will be replaced with pure black.

Next, go to the Quality tab. By clicking on the “Enhance” button, set the Cleaner passes parameter to one. Uncheck the Protect black pixels option. Enclose the grayed-out illustrations in the scan in the Exclude zone to protect them from damage.

Take advantage of a preview of the results of clearing the gray background using the “Preview with resample” button in the Quality tab. Select the desired Sensitivity value (from 5 to 30) to remove the gray background. The stronger the contrast between the background and the text, the higher the value of this parameter. Now go to the Protect black window, disable it.

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