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View Full Version : Duet Controller artwork quality - no dithering done?



pnielsen
2008-03-08, 15:27
According to the specifications, the Controller has a 256K color display (should that really be 256,000 or 256?), yet the quality of displayed colors is nowhere near what it could be on a 256 color screen. The display quality makes me guess the image is quantized to a fixed set of colors without follow-up by error dithering to correct quantization errors.

A 256 color display can display images much better than what the Controller currently does. The trick is to apply dithering to compensate for the quantization error. (For instance Floyd-Steinberg dithering is excellent - sample code can be found in the libjpeg package).

If the Controller uses a LCD with 256K colors, then the problem is possibly the lack of error dithering to compensate for bit truncation done by the LCD.

I have scanned all my album coverart in 700x700 pixels (150dpi) and store them in JPEG format.

The defects show up more obvious on some artwork than other. I have attached images of the artwork of one of my CDs where the defects are obvious. I reduced the size to 300x300 pixels since that's sufficient to clearly show the problem.

First image: Source image provided to SqueezeCenter

Second image: Source image converted to a palette of 256 fixed colors without using error dithering. THIS IS A GOOD APPROXIMATION OF HOW THE CONTROLLER DISPLAYS THE ARTWORK. The color errors are in the same locations and of the same type.

Third image: Source image converted to a palette of 256 fixed colors using Floyd-Steinberg error dithering. Looks much better, doesn't it?

Thoughts? Is the problem what I suggest it is? Any chance this will be improved?

Thanks,
Peter

The two similated images were created with PMView Pro avalaible at www.pmview.com. Note that the Forum software converted my two original 256-color GIF images to JPEG.

radish
2008-03-08, 16:02
The SBC display is certainly capable of very good quality images, just take a look at the flickr screensaver or some of the background images for examples. I personally don't think the issue point out is due to colour space reduction (24bit vs ~18bit really isn't much of a visible difference) but due to a non-resampling (or at least non-optimal) resize. Going from 700x700 (or whatever) to something like 150x150 is a big drop and will lead to aliasing and contouring if not resampled properly, which I also notice on some artwork.

pnielsen
2008-03-08, 16:20
Good point. However, colors normally will not suffer from size reduction even when a very crude pixel dropping method is used. I just tried resizing to 150x150 without interpolation (=pixel dropping in PMView) and the only obvious defect is jagged edges, which is what to expect. Colors are 100% ok.

The errors I see in the SBC Artwork display are those of color reduction from 24-bit to 256 colors without using error correction dithering.

You're right about 18 bits (256K colors). Errors would be very subtle. (The GIF file format is limited to 18 color bits, 6 per R/G/B, and a GIF of the same file looks perfectly fine without any obvious flaws).

So, if the display really is 18-bit, why are they converting to 256 colors, or what bad code is there to generate the obvious defects? The SBC is great, but the poor artwork display quality is a major disappointment.

Peter

dean
2008-03-08, 17:17
The SBC display is actually 16-bit.

The images are converted to 24-bit GD format, which is essentially raw, then sent to the SBC and displayed as 16-bit (5-6-5). There is some banding, but I don't think that it's as bad as the example you posted.

The SBC doesn't do any dithering, but it probably should. (The dithering could also happen on the server side, it's not obvious to me where it should happen.)

Can you file a bug on http://bugs.slimdevices.com and attach the original image that you are having problems with?

pnielsen
2008-03-08, 17:56
There is some banding, but I don't think that it's as bad as the example you posted.?

The problem I'm seeing is not banding. I know what banding is, and the SBC does not display the image nearly as well as a 5-6-5 display would.


The SBC doesn't do any dithering, but it probably should.

I don't think that's necessary. A 5-6-5 display should provide adequate results for MOST images. Only images with gradients will show banding.


Can you file a bug on http://bugs.slimdevices.com and attach the original image that you are having problems with?

Thanks. I will do that. Obviously the software is doing some really bad things with the image before it's sent to the SBC.

Now I'm guessing that it might be converted to 8-bits to limit bandwith and save processing time in the SBC. If this is the case, the conversion to 8-bits (256 colors) is done very poorly!

Thanks,
Peter

pnielsen
2008-03-08, 18:16
Here's a photo of the SBC taken with my Canon G9.

dean
2008-03-08, 18:36
On Mar 8, 2008, at 4:56 PM, pnielsen wrote:
>> Can you file a bug on http://bugs.slimdevices.com and attach the
>> original image that you are having problems with?
>
> Thanks. I will do that. Obviously the software is doing some really
> bad
> things with the image before it's sent to the SBC.
>
> Now I'm guessing that it might be converted to 8-bits to limit
> bandwith
> and save processing time in the SBC. If this is the case, the
> conversion
> to 8-bits (256 colors) is done very poorly!
It really should be an uncompressed 8888 RGBA image, resized on the
server.

Let's take a look at that image and see what's going on...

pnielsen
2008-03-08, 20:34
I was going to open up a bug report, however, what category should I open it under? There is no specific category for the SBC...

Here are two images that clearly show the problem in the SBC when used as artwork source files in SqueezeCenter 7.0 GA. (I can easily find more examples if needed). I gzip:ed them as the forum software seems to be broken and corrupts zip files.

Can you repeat the problem?

Thanks,
Peter

kdf
2008-03-08, 20:45
On 8-Mar-08, at 7:34 PM, pnielsen wrote:

>
> I was going to open up a bug report, however, what category should I
> open it under? There is no specific category for the SBC...

Jive Software, UI component.

the Controller was formerly known as Jive.

-kdf

bradjudy
2008-03-08, 21:13
I've had similar experiences with album covers with similar backgrounds.

pnielsen
2008-03-08, 21:21
I've opened bug report #7462

Thanks,
Peter

peter
2008-03-09, 02:28
pnielsen wrote:
> Here's a photo of the SBC taken with my Canon G9.
>

Looks familiar. I've seen this kind of 'effect' too, I blamed it on the
source material, never investigated.

Regards,
Peter

dean
2008-03-09, 08:13
Thanks for the pictures. I'm playing with it in photoshop and put
your image up on the Controller screen.

I see a couple of things:

1. The color banding effects are strong with this particular image.
I was able to reproduce the color pattern closely in photoshop with 32
levels of posterization (approximately 555 encoding). The quality of
the image is definitely improved with a 565 dither.

2. The photo you took appears to be taken from slightly above
perpendicular to the screen. The viewing angle on the Controller LCD
is better from the natural angle when holding the device in your hand,
slightly _below_ perpendicular. I was able to verify that the image
looks a much better when viewed normally in the hand.

So the takeaway is that we can do better by doing a proper dither on
the device from 888 to 565. Also, the viewing angle matters.

bradjudy
2008-03-09, 08:37
2. The photo you took appears to be taken from slightly above
perpendicular to the screen. The viewing angle on the Controller LCD
is better from the natural angle when holding the device in your hand,
slightly _below_ perpendicular. I was able to verify that the image
looks a much better when viewed normally in the hand.

So the takeaway is that we can do better by doing a proper dither on
the device from 888 to 565. Also, the viewing angle matters.

I have noticed that the images look much better at an angle, but it's pretty extreme. The dither issue is quite obvious at perpendicular and the ideal angle seems to be about 45 degrees. Given the function of the device (it's iPod like in use, not a remote control that needs to be pointed), the natural viewing angle for me is perpendicular, not at a steep angle.

pnielsen
2008-03-09, 12:29
So the takeaway is that we can do better by doing a proper dither on the device from 888 to 565. Also, the viewing angle matters.

Great! I believe this will take care of the problem. Please use Floyd-Steinberg dithering (or an equally good method).

BTW, what is the size of the artwork displayed by the SBC?

Is it possible to use a lossless format (e.g. PNG, BMP, or GIF) instead of JPG for the artwork? If this is possible, I'm going to try converting the source files to the native size of the SBC and use 5-6-5 Floyd-Steinberg dithering.

Thanks,
Peter

ptrainer
2008-03-13, 23:50
Any headway on this issue? Almost all of my album artwork that has any significant area of white or extremely light areas blending into darker show these unattractive artifacts. I do hope it can be corrected.

Kim.T
2008-04-21, 04:20
BUMP
I see that there has been no movement in the bug report 7462. Is there any news on this issue ? I have the same problem with a lot of my artworks.

Schindler
2009-03-17, 04:30
Any news on this matter, the bugreport also is quiet...

Christian

lord_squeeze
2010-01-31, 09:10
Would love to see this fixed...

Mnyb
2010-01-31, 09:22
Would love to see this fixed...

Vote on the bug:

https://bugs.slimdevices.com/show_bug.cgi?id=7462

SBC looks really weird with bright white or red covers, then it gets all blocky and pixelated.

Only twelve voters ? even if its pretty obvious that the screen does not render colors correctly ? or I'm I picky and expects to much ?

lord_squeeze
2010-01-31, 10:18
Vote on the bug:
https://bugs.slimdevices.com/show_bug.cgi?id=7462

Only twelve voters ? even if its pretty obvious that the screen does not render colors correctly ? or I'm I picky and expects to much ?
Voted.

You are not picky. I noticed the bug during the first two minutes of using the Controller. I was shocked -- SHOCKED!!-- ;) to see it has been around since 2008 and still not fixed.

Mnyb
2010-01-31, 10:41
Voted.

You are not picky. I noticed the bug during the first two minutes of using the Controller. I was shocked -- SHOCKED!!-- ;) to see it has been around since 2008 and still not fixed.

Baah there are 9 year old bugs in the system ;) targeted for future, thats probably entirely correct. There is always more future if you belief the theory that the rate off expansion in the universe is accelerating (no big crunch )

usch
2010-01-31, 11:19
Since the Controller uses the same display as the Radio, shouldn't that effect be visible there, too?

Mnyb
2010-01-31, 12:12
Since the Controller uses the same display as the Radio, shouldn't that effect be visible there, too?

Different cpu and probably other system differences on the hardware level, I can not compare have no radio yet.
But if they solved it on the radio and NOT backported it to the controller, i would get grumpy officially.

Mnyb
2010-01-31, 12:28
But the problems is clearly visible in this pictures:

Note: forum prevent to large pictures so I've resized,but you can still see the artifacts

finnbrodersen
2010-01-31, 12:36
Hi

I must agree, that the display quality of album art leaves much to be desired.

Overall the display quality of the user interface looks good, the letters are good and sharp, but this is not the case with album art, which has too many artifacts.

Another problem is the narrow viewing angel of the display, but I think this is a hardware problem, which can not be solved in sw.

running SBS 7.4.2-r29959 on WinXP with SBC on fw 7.4.1 r7915