Grayscale
Convert colour pages to greyscale
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Note: the result becomes an image, so its text will no longer be searchable.
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PDF document · Up to 100 MB
How do you convert a PDF to black and white?
Colour pages are converted to greyscale, which makes printing cheaper. The work is done by redrawing each page as an image. The result is therefore a document made of images: the text in it can no longer be searched, copied or read by screen readers — and that change cannot be undone.
What greyscaling does not do
- It does not keep the text layer — searching and copying stop working.
- It does not guarantee a smaller file and often makes it larger.
- It cannot be undone — keep the original file.
Worked example: what happened to the text
Text was extracted from a 3-page document first: 3 page blocks and 55 characters were found. The same document was then converted to greyscale and the text extractor was run over the result — this time no text was found at all and the document was judged to be a scan. The file did not get smaller either: from roughly 1.8 KB it grew towards 10 KB.
Printing the bound copies
Before a defence a dissertation is printed in several copies and bound, while the avtoreferat circulates in a larger run still. Colour printing costs noticeably more than black and white, and colour charts in appendices come out grey in a black and white run anyway. Converting the pages to greyscale in advance avoids unexpected colour leaves at the print shop. But this applies only to the printed copy. Never greyscale the file that goes to a journal, to a portal or to a plagiarism check: the checking system reads the text layer, and a redrawn document cannot supply text. Keep the original colour file separately — there is no way back.
Questions about converting a PDF to black and white
Why did the text stop being searchable?
Because the pages were redrawn as images. In testing, 55 characters were extracted from the original document and nothing at all from the greyscale copy. If you need the text, save it first with the Extract text from PDF tool.
Will the file get smaller?
Usually not. A grey image is smaller than a colour one but larger than a text page. In testing a small text document grew instead. If the goal is a smaller file, use the Compress PDF tool.
Can the change be undone?
No. The result is a new file, so your original document stays where it is, but colour and the text layer cannot be recovered from the greyscale copy. That is why saving a copy before you start is advised.
Can I apply this to the file I send to a journal?
It is not advisable. Journals and plagiarism-checking systems read the text layer, and a greyscale copy has none. This tool is for the printed copy, not for the file you submit.