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If you save this image on your desktop, you see it's background color as your desktop color. If you open it with Adobe Photoshop, its background id checkered which means it has no background. It's transparent.

The background data is removed and I think this image has this size without any compression because no lag in zooming compared to the same image with white background (you can find it through trial and error and converting it to different formats with different compressions) which leads to faster scrolling speed when converted to PDF. How we can do it?

How to produce a 1-bit transparent gif?

By the way, in archive.org it's recognized as animated gif.

enter image description here

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Why this scanned book image has no background?

Whoever produced it set it's background to be transparent.

This is a feature of several image file formats. sometimes it is referred to as an alpha channel (which provides degrees of transparency) some tools/formats simply allow for one color to be selected and marked as fully transparent.

GIF supports index transparency, which is the latter type.

How we can do it?

For simple index transparency,iIn many tools you can choose a transparency option when you save a file.

enter image description here
Example of save options in IrfanView

  • I adjust output as transparent 1-bit color (black and white), but my output file become 8-bit. Why? – living being Jan 24 '15 at 13:29

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