I would like to resize the images of my cbz/cbr on PC so that they are optimized for Kobo Touch. This means they won't be resized by the device, because the width or height are set to the maximum available value.
I've read
this thread, where it is said that the resolution is 600x800.
I made a test to verify this. I've created an image with a black and white checkboard with 1px square size, and saved it in PNG (grayscale and RGB).
The image was than cropped to create:
- images with fixed height (200px) and increasing width (from 591px to 610px) to test the horizontal resolution
- images with fixed width (200px) and increasing height (from 791px to 810px) to test the vertical resolution. The images was archived in the attached file (rename as .cbz to test), so that:
- images 1 to 20 are grayscale images with increasing width
- images 21 to 40 are grayscale images with increasing height
- images 41 to 60 are RGB images with increasing width
- images 61 to 80 are RGB images with increasing height
Reading the cbz image on the Kobo, with refresh on every page turn, I've seen that:
- almost all images creates visual artifacts, due to resize operations by the device. The cleaner images are the ones with width=600px and the ones with height=800px
- the images are rendered in different ways if I turn the pages forward or backwards (?!?!?)
- grayscale and RGB images are displayed in the same way (regarding the resolution)
Sooooo, it seems that 600x800 images won't be resized by the Kobo Touch. So images will be displayed as-is (not resized) if they have width=600 and height<=800, or height=800 and width<=600.
What do you think about it?
Can you test the attached file and share your opinion?
!BEWARE! The Kobo automatically turn the first image, that is an horizontal image, by 90° (to maximize its size on the display). Remember to turn it again in it's original position to make the test correctly! After that, the other images are displayed correctly.
NOTE: I will remark that I'm talking about CBZ/CBR archives, NOT ePub books (where images maximum size may vary due to margins and other settings)