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Re: [OT] scanned files are large in size




On Tue, Jan 1, 2019 at 7:40 PM <tomas@xxxxxxxxxx> wrote:
On Tue, Jan 01, 2019 at 12:34:38PM -0500, kamaraju kusumanchi wrote:
> A scanned document from Canon pixma mx870 printer is significantly
> larger compared to the same document scanned on a different scanner.
> When I look at both the images side by side on a PC, there is no
> visual difference between the two. I am trying to understand the
> underlying cause and fix it if possible.
>
> As shown below, scanned_in_office.pdf is 332Kb, scanned_on_mx870.pdf is 1.7 Mb.
>
> % ls -al scanned_in_office.pdf scanned_on_mx870.pdf
> -rw-r--r-- 1 rajulocal rajulocal  331796 Jan  1 11:54 scanned_in_office.pdf
> -rw-r--r-- 1 rajulocal rajulocal 1775460 Jan  1 11:48 scanned_on_mx870.pdf

Yep. The one image is encoded as CCITT (aka Group 4, aka fax [1]), which is
passable for low res B&W images, but not that much for hi-res or color (or
gray scale). It compresses much worse than the other which is JPEG, which is
expressly made for hi-res and color (or grayscale) images.

OTOH, CCITT is lossless and JPEG lossy ;-)

Not sure what you mean by "compresses much worse" here, but the CCITT version is much smaller than the JPEG version. Maybe you meant that CCITT looks worse after compression, which is weird when you also write that CCITT is lossless!