grayscale conversion

Mikemk · 02-24-2016, 07:18 AM

How can I tell calibre to convert all images to grayscale (16-level) during a bulk convert?

EDIT: Including covers

theducks · 02-24-2016, 09:28 AM

I will bite.

Why?
Modern devices (>2009) will greyscale (display) a color image just fine.
I can not believe a 16 bit Greyscale will save that much filesize over the same size color image.

Preferences: (to set system FIRST TIME Conversion default)
Conversion: (to control or override defaults for the current book only)
Common Options: Page setup: Output Profile (hover over device model for details)

dwig · 02-24-2016, 04:07 PM

Quote:

Originally Posted by theducks

...
I can not believe a 16 bit Greyscale will save that much filesize over the same size color image.
...

16 LEVEL = 4bit, not 16bit

The difference would depend largely on the bit depth of the original color image and the compression type and degree used for both the original color and the new greyscale.

At matching bit depths and uncompressed, the greyscale image would be roughly 1/3rd the size of the color, assuming that the files' metadata headers and any ancillary data is small. This could add up to a large total difference if there are a lot of images.

Mikemk · 02-24-2016, 10:34 PM

Quote:

Originally Posted by dwig

16 LEVEL = 4bit, not 16bit

The difference would depend largely on the bit depth of the original color image and the compression type and degree used for both the original color and the new greyscale.

At matching bit depths and uncompressed, the greyscale image would be roughly 1/3rd the size of the color, assuming that the files' metadata headers and any ancillary data is small. This could add up to a large total difference if there are a lot of images.

Such as a comic book

I've found a way to convert .cbz to grayscale, but not the cover or other file formats.

kovidgoyal · 02-24-2016, 10:38 PM

When you are converting comics there is an option to grayscale the images. There is no option to do that for regular books, since regular books rarely have large numbers of large images. If your book is in epub or azw3 format, you can simply use the unpack book tool in calibre and then any bulk image processing utility to grayscale images.

02-24-2016, 07:18 AM	#1
Mikemk Member Posts: 16 Karma: 10 Join Date: Feb 2016 Device: Kindle Touch 2011 & KT 2017	grayscale conversion How can I tell calibre to convert all images to grayscale (16-level) during a bulk convert? EDIT: Including covers Last edited by Mikemk; 02-24-2016 at 08:13 AM.

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02-24-2016, 09:28 AM	#2
theducks Well trained by Cats Posts: 30,939 Karma: 60358908 Join Date: Aug 2009 Location: The Central Coast of California Device: Kobo Libra2,Kobo Aura2v1, K4NT(Fixed: New Bat.), Galaxy Tab A	I will bite. Why? Modern devices (>2009) will greyscale (display) a color image just fine. I can not believe a 16 bit Greyscale will save that much filesize over the same size color image. Preferences: (to set system FIRST TIME Conversion default) Conversion: (to control or override defaults for the current book only) Common Options: Page setup: Output Profile (hover over device model for details)

02-24-2016, 10:38 PM	#5
kovidgoyal creator of calibre Posts: 45,251 Karma: 27110894 Join Date: Oct 2006 Location: Mumbai, India Device: Various	When you are converting comics there is an option to grayscale the images. There is no option to do that for regular books, since regular books rarely have large numbers of large images. If your book is in epub or azw3 format, you can simply use the unpack book tool in calibre and then any bulk image processing utility to grayscale images.

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