602 FBreader : a different way of displaying images ?

[Tulapi]

Hi,

I noticed that FBreader doesn't seem to display images the same way as the main image viewer.
I have attached two photographs of the same image (sorry, the quality is not good) :
- displayed by the image viewer
- displayed by FBreader (I have put the image in a html file)

As you can see, the difference is quite appreciable. The dithering seems very different.

Do you any way to force FBreader to use the default image viewer ?

thank you,
Tulapi.
(thanks to the many great people in this forum)

[Roos]

I don't know a answer for you, i myself would be happy if i could only get FBreader to display the cover of the book, and the text in the right formatting
But after looking at the last 2 images i understand your pain, ouch, the last one looks like its build of lego blocks

[mtravellerh]

Originally Posted by Roos

I don't know a answer for you, i myself would be happy if i could only get FBreader to display the cover of the book, and the text in the right formatting
But after looking at the last 2 images i understand your pain, ouch, the last one looks like its build of lego blocks

Yes, fbreader renders the images in 8 shades instead of 16. Maybe there is a way to chnge that but I'm not aware of a possibility (then again, i'm not a technician or a proggie) Of course, illustrations tend to be smaller and thus tend to look smoother.

[Tulapi]

The difference seems to be not only in the number of shades of grey, but also in the dithering. In FBreader it seems to be different and very strong. Look at the vertical/horizontal patterns in the fbreader image.

But there is a thing I don't understand :
The default image viewer is not implemented in the main reading application. So what is the use of this image viewer ? I don't think that many people bought a Pocketbook device to watch their family pictures in black and white. No ?


Anyway, thank you for your answer.

[mtravellerh]

Originally Posted by Tulapi

The difference seems to be not only in the number of shades of grey, but also in the dithering. In FBreader it seems to be different and very strong. Look at the vertical/horizontal patterns in the fbreader image.

But there is a thing I don't understand :
The default image viewer is not implemented in the main reading application. So what is the use of this image viewer ? I don't think that many people bought a Pocketbook device to watch their family pictures in black and white. No ?


Anyway, thank you for your answer.

Well, I know that the image viewer is also used by some to read comics and the like. Apart from that, some seem to use their PB as a viewer for pictures, yes.

[rkomar]

Originally Posted by Tulapi

The difference seems to be not only in the number of shades of grey, but also in the dithering. In FBreader it seems to be different and very strong. Look at the vertical/horizontal patterns in the fbreader image.

It's probably not dithering that's going on, but rescaling of the image. If the scaling algorithm is just taking the closest pixel from the source image and copying it to the scaled image (i.e. nearest-neighbour scaling), then you can get the kind of artifacts that you see. Area averaging produces better output, but is slower. Since some people here are working on improving fbreader for the pb devices, maybe someone can add a more accurate scaling method and merge it in with the good/fast rendering options offered in the menu.

[Tulapi]

Yes, rescaling seems to have an important effect. I tested different sizes of images. The pattern is always here, but it changes.
The pattern seems to be stronger with big images.

[rkomar]

Originally Posted by Tulapi

Yes, rescaling seems to have an important effect. I tested different sizes of images. The pattern is always here, but it changes.
The pattern seems to be stronger with big images.

If the image is a scan from a publication, then maybe it would help if you despeckled it. Those often produce a moire effect when the image is rescaled using the nearest-neighbour algorithm.

[Tulapi]

It is not a scanned image. There was a pattern with every kind of image I have tested, not only the one I have attached.

[wallcraft]

Originally Posted by Tulapi

It is not a scanned image. There was a pattern with every kind of image I have tested, not only the one I have attached.

For the longest time, FBReader did no processing of images at all. It just centered them and displayed them "as is" - no dithering and no rescaling. I don't think the standard Desktop FBReader does dithering even today, but it does rescale images that are too big to fit on the screen. Have you tried images that are smaller than the available screen resolution?

I am not convinced that nearest neighbor dithering can produce artifacts this bad unless the original image was very small. So perhaps Pocketbook's FBREader is also magnifiying images.

[Tulapi]

With small images (300 px here), the pattern is still there.

[GrayNM]

Tulapi
Yes, FBReader uses dithering.
The simple algorithm with fixed pattern, as you can see.

I suppose that was done because FBReader works in 2-bit color mode.
That's correct at least for PB301/360. I didn`t see FBReader sources from Pro series, but I think they remain the same.
The main reason behind using 4-color mode in FBreader is the speed. 8- or 16-color modes are much slower.

Image viewer uses best available mode so it doesn't needed to use so aggressive dithering. But there is no reason to use the same mode in the text reader.

[rkomar]

Originally Posted by Tulapi

With small images (300 px here), the pattern is still there.

That looks like dithering rather than nearest-neighbour sampling effects. Sorry about the misdirection.

[Tulapi]

Originally Posted by GrayNM

I suppose that was done because FBReader works in 2-bit color mode.
That's correct at least for PB301/360. I didn`t see FBReader sources from Pro series, but I think they remain the same.
The main reason behind using 4-color mode in FBreader is the speed. 8- or 16-color modes are much slower.

Image viewer uses best available mode so it doesn't needed to use so aggressive dithering. But there is no reason to use the same mode in the text reader.

I guess it is a matter of taste : some people will prefer speed, some others like me will prefer more beautiful images. But...
When I open an epub (I have converted my previous html file with Calibre) with Adobe Viewer in my 602, it doesn't seem to be slower than fbreader when displaying an image. And Adobe Viewer seems to use more colors, maybe 8 or 16 : the image is clearly smoother and more beautiful.
(The problem with Adobe Viewer is that it can't open html files...)

So maybe it would be nice to have a option for a 16-colors mode in fbreader, as it may not impact too much the speed (at least for the 60x/90x series). Do you think it would be very difficult to implement ?

[wallcraft]

Originally Posted by GrayNM

Tulapi
Yes, FBReader uses dithering.
The simple algorithm with fixed pattern, as you can see.

I suppose that was done because FBReader works in 2-bit color mode.
That's correct at least for PB301/360. I didn`t see FBReader sources from Pro series, but I think they remain the same.
The main reason behind using 4-color mode in FBreader is the speed. 8- or 16-color modes are much slower.

Image viewer uses best available mode so it doesn't needed to use so aggressive dithering. But there is no reason to use the same mode in the text reader.

The very idea that the best way to use a device with 4-bit (16 gray level) hardware is to dither 2 bits (4 gray levels) is strange. The iRex iLiad ran FBReader with 16 gray levels years ago. It did no dithering, and sometimes this was sub-optimal but it was never a terrible approach. It also took a long time to turn a page, but this should not be an issue with modern ebook reader hardware.