Why does my Aura HD mess up the colours on my cover images?

ownedbycats · 11-10-2020, 05:00 AM

While trying to troubleshoot what I thought was a Calibre issue, I found that using Kobo Utilities to delete all the covers and re-generating them on the device itself resulted in all the colours getting the RGB values swapped. (It took me a while to figure out because the Aura HD is eInk and thus in greyscale).

It doesn't happen when I upload the covers...guess I'll be doing that. But is this normal behaviour?

davidfor · 11-10-2020, 08:22 AM

Did they look wrong on the device? Or did you only notice them because you looked at them using calibre?

I have seen this in the past. From memory, the covers displayed correctly, so I assumed the image handling was being done properly.

NiLuJe · 11-10-2020, 09:44 AM

The Kobo fb is indeed setup in BGR order, not RGB.

Code:

red:   bitfield offset: 16, bitfield length: 8, MSB is right: no
green: bitfield offset: 8, bitfield length: 8, MSB is right: no
blue:  bitfield offset: 0, bitfield length: 8, MSB is right: no
alpha: bitfield offset: 24, bitfield length: 8, MSB is right: no

Pixel format details:
B: 0 / G: 1 / R: 2 / A: 3 (i.e., BGRA)
Should alpha be honored? Yes.

This is *mostly* harmless since the display is ultimately grayscale, but it does minimally affect the grayscaling process, as red usually isn't weighted the same as blue, no matter how you choose to grayscale.

The point is entirely moot (outside of in-book content) once you've setup Calibre to handle the grayscaling on its own for covers thumbnails

.

NiLuJe · 11-10-2020, 09:50 AM

Which leads me to my next question: I'm actually pretty sure Kobo "fixed" it to actually make it consistent with what the framebuffer expects, so, *what* did you check, exactly?

(The generated files in .kobo_images? A Nickel screenshot? An fbgrab?).

NiLuJe · 11-10-2020, 10:01 AM

Okay, curiosity got the better of me.

ePubs: The covers are generated grayscale, with a crappy dithering pattern.
KePubs: The covers are generated BGRA (which is good).

And, what actually matters: Nickel itself grayscales everything now, so the point is doubly moot.

ownedbycats · 11-10-2020, 11:35 AM

Quote:

Originally Posted by davidfor

Did they look wrong on the device? Or did you only notice them because you looked at them using calibre?

I have seen this in the past. From memory, the covers displayed correctly, so I assumed the image handling was being done properly.

They looked ok on the device - it was on Calibre that they appeared wrongly.

Quote:

Originally Posted by NiLuJe

Which leads me to my next question: I'm actually pretty sure Kobo "fixed" it to actually make it consistent with what the framebuffer expects, so, *what* did you check, exactly?

(The generated files in .kobo_images? A Nickel screenshot? An fbgrab?).

I was looking at the cover in the device view of Calibre.

NiLuJe · 11-10-2020, 11:38 AM

Then everything's peachy, that's the way they ought to look for a Kobo

.

11-10-2020, 05:00 AM	#1
ownedbycats Custom User Title Posts: 10,988 Karma: 75337983 Join Date: Oct 2018 Location: Canada Device: Kobo Libra H2O, formerly Aura HD	Why does my Aura HD mess up the colours on my cover images? While trying to troubleshoot what I thought was a Calibre issue, I found that using Kobo Utilities to delete all the covers and re-generating them on the device itself resulted in all the colours getting the RGB values swapped. (It took me a while to figure out because the Aura HD is eInk and thus in greyscale). It doesn't happen when I upload the covers...guess I'll be doing that. But is this normal behaviour?

11-10-2020, 09:44 AM	#3
NiLuJe BLAM! Posts: 13,506 Karma: 26047202 Join Date: Jun 2010 Location: Paris, France Device: Kindle 2i, 3g, 4, 5w, PW, PW2, PW5; Kobo H2O, Forma, Elipsa, Sage, C2E	The Kobo fb is indeed setup in BGR order, not RGB. Code: red: bitfield offset: 16, bitfield length: 8, MSB is right: no green: bitfield offset: 8, bitfield length: 8, MSB is right: no blue: bitfield offset: 0, bitfield length: 8, MSB is right: no alpha: bitfield offset: 24, bitfield length: 8, MSB is right: no Pixel format details: B: 0 / G: 1 / R: 2 / A: 3 (i.e., BGRA) Should alpha be honored? Yes. This is mostly harmless since the display is ultimately grayscale, but it does minimally affect the grayscaling process, as red usually isn't weighted the same as blue, no matter how you choose to grayscale. The point is entirely moot (outside of in-book content) once you've setup Calibre to handle the grayscaling on its own for covers thumbnails .

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11-10-2020, 08:22 AM	#2
davidfor Grand Sorcerer Posts: 24,905 Karma: 47303824 Join Date: Jul 2011 Location: Sydney, Australia Device: Kobo:Touch,Glo, AuraH2O, GloHD,AuraONE, ClaraHD, Libra H2O; tolinoepos	Did they look wrong on the device? Or did you only notice them because you looked at them using calibre? I have seen this in the past. From memory, the covers displayed correctly, so I assumed the image handling was being done properly.

11-10-2020, 09:50 AM	#4
NiLuJe BLAM! Posts: 13,506 Karma: 26047202 Join Date: Jun 2010 Location: Paris, France Device: Kindle 2i, 3g, 4, 5w, PW, PW2, PW5; Kobo H2O, Forma, Elipsa, Sage, C2E	Which leads me to my next question: I'm actually pretty sure Kobo "fixed" it to actually make it consistent with what the framebuffer expects, so, what did you check, exactly? (The generated files in .kobo_images? A Nickel screenshot? An fbgrab?).

11-10-2020, 10:01 AM	#5
NiLuJe BLAM! Posts: 13,506 Karma: 26047202 Join Date: Jun 2010 Location: Paris, France Device: Kindle 2i, 3g, 4, 5w, PW, PW2, PW5; Kobo H2O, Forma, Elipsa, Sage, C2E	Okay, curiosity got the better of me. ePubs: The covers are generated grayscale, with a crappy dithering pattern. KePubs: The covers are generated BGRA (which is good). And, what actually matters: Nickel itself grayscales everything now, so the point is doubly moot.

11-10-2020, 11:38 AM	#7
NiLuJe BLAM! Posts: 13,506 Karma: 26047202 Join Date: Jun 2010 Location: Paris, France Device: Kindle 2i, 3g, 4, 5w, PW, PW2, PW5; Kobo H2O, Forma, Elipsa, Sage, C2E	Then everything's peachy, that's the way they ought to look for a Kobo .