Am I missing something? (Image conversion for eips and others)

[Richy_T]

First off, I want to say thanks to everyone for all the information which has helped me get my kindle jailbroken (and I think you guys did before when I did one many moons ago).

I'm not meaning to step on any toes here but I think I'm seeing a mistake repeated and just want to check in (it could be me misunderstanding).

So when people are converting images for display on eips with ImageMagick, they are converting to 8 bit PNG and it's working fine (and it works for me). However, I am seeing this parameter in the examples I see on this site.

-dither FloydSteinberg

Now, that's a fine dithering option. However, it's my understanding that without the colors option, it won't properly compress the color space, you'll have 256 levels of grey, stored in 8 bits and no dithering so you'll get banding etc (my testing indicates this to be the case. I could probably post pics). This needs to be changed to

-dither FloydSteinberg -colors 16

which will drop the levels to 16 and allow the error correction to occur.

I would also suggest trying the other options for dithering as some work better for some images than others (I did some work a few years back dithering images for thermal printers)

Edit: Interestingly, when I google for the correct form, I get two results which are not from this site, but do link back here (but not to anything apparently relevant)

[knc1]

Have you read all of the things geekmaster has posted here on dithering?

The examples you quote are only that, examples, which may contain typo's.
Check the actual scripting in the screensaver package that is used to process covers.
And also my FGA thread which includes the subject of target sizes.
I honestly don't recall what all information I linked too.

[Richy_T]

Originally Posted by knc1

Have you read all of the things geekmaster has posted here on dithering?

The examples you quote are only that, examples, which may contain typo's.
Check the actual scripting in the screensaver package that is used to process covers.
And also my FGA thread which includes the subject of target sizes.
I honestly don't recall what all information I linked too.

I have not. I have read his stuff on framebuffers and looked through his movie player stuff (really cool to see that on a Kindle and some really succinct code too). I haven't been here that long to have gone the full depth but I have been looking for that dithering stuff (due to the way I plan to implement what I do) and saw it wrong in several places and even relinked a few times and never called out. As I say, not intending to step on any toes, just trying to get good info out there.

[s]Edit: That thread has good info but it is one of the ones where NiLuJe posts the incorrect code (while correctly stating to dither to 4 bits)[/s]

Never mind, I see where my issue is. NiJuLe uses the -remap parameter which will have the effect of reducing the colorspace. The command I was using did not have that so I must have picked it up from someone who got it wrong.

[knc1]

Originally Posted by Richy_T

- - - -
Never mind, I see where my issue is. NiJuLe uses the -remap parameter which will have the effect of reducing the colorspace. The command I was using did not have that so I must have picked it up from someone who got it wrong.

I think that option also reduces 256 bit mapped colors.

Which would be one of the reasons he uses it, there where a lot of trouble reports from people whose graphic program, unknown to them, was including a color mapping table.

[Richy_T]

Originally Posted by knc1

I think that option also reduces 256 bit mapped colors.

Which would be one of the reasons he uses it, there where a lot of trouble reports from people whose graphic program, unknown to them, was including a color mapping table.

I'm not sure. I think sending it greyscale possibly takes care of that. The images were displaying fine without the -remap or -colors, they just weren't dithered. Though it is likely or at least possible that it matches the output of the Kindle screen better than just -colors which I guess just uses a linear adjustment.