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 > > Both are are scanned at 600 dpi. The only difference I see is in bpc, > enc fields. 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 ;-) > Questions: > 1) Does the large file size have anything to do with the printer > itself? Is there anything I can do (ex:- update the driver/firmware or > something)? That depends on what is encoding the images: does the scanner itself "make" the PDF? Or some software, computer-side? > 2) Is the difference in image sizes due to the bpc (1 vs. 8) or > encoding (ccitt vs jped) fields? CCITT vs JPEG, yes. > 3) If yes, how to change them? Hmmm. I don't know yet whether you have to talk to your scanner or to your scan software... Cheers [1] https://en.wikipedia.org/wiki/Group_4_compression -- tomás
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