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Old 12-16-2011, 12:44 PM   #1
pruss
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Kindle Fire subpixel rendering bug

I wonder if anybody else has noticed that the Kindle Fire's official ebook reader incorrectly does subpixel rendering in reversed landscape mode (landscape mode with the power button on the left).

The result is colorful shadows beside letters. No such shadows occur in the browser--it's a problem solely with the Kindle app.

I just sent them feedback about this.

There may also be a subtler effect in reversed portrait mode, but I am not so sure.

p.s. Does the Kindle Fire index books for searching? I did a search in the included dictionary and it was very slow, more like the super-slow search in the Android Kindle app, and not like a "real" Kindle.

Last edited by pruss; 12-16-2011 at 12:47 PM.
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Old 12-16-2011, 12:57 PM   #2
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Just sent this followup email:

I just sent you an email about subpixel rendering.

I tested a little more carefully. I had made an incorrect assumption about the subpixel orientation in my previous email.

Anyway, my current testing shows that the problem occurs in reversed landscape mode (landscape mode with the power button on the left), not in regular landscape mode. In regular landscape mode we have correct subpixel rendering.

Taking a 15X magnifying glass to the screen, I also see that there is incorrect subpixel rendering in portrait and reverse portrait. I can barely see this effect naked eye in portrait mode, but I can definitely see it naked eye in reverse portrait. In portrait and reverse portrait mode the actual hardware subpixel arrangement is vertical (I made an incorrect assumption in my other email), but based on what I see under the magnifying glass, your software treats the screen as if it were a horizontal RGB subpixel display.

In other words, it's looking to me that the font renderer uses the very same subpixel mode for all four screen rotations, and that is a no-no. You need to either switch subpixel mode based on the rotation (RGB for normal landscape, BGR for reversed landscape, and vertical modes for portrait), or turn off subpixel rendering altogether for all rotations, or have subpixel rendering for regular landscape and off for all other rotations. Incorrect orientation subpixel rendering is worse than no subpixel rendering.
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Old 12-16-2011, 09:46 PM   #3
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Very interesting, I wonder if the improper shadowing might cause the eye strain problems that a few folks are worried about. I'm switching to landscape for a few days to see if there is a noticeable difference.
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Old 12-16-2011, 11:22 PM   #4
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I got eyestrain from looking at the screen with a magnifying glass. :-)
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Old 12-16-2011, 11:57 PM   #5
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Very interesting, I wonder if the improper shadowing might cause the eye strain problems that a few folks are worried about. I'm switching to landscape for a few days to see if there is a noticeable difference.
The eye strain is caused by the background being too bright unlike the stock Kindle Android app the Fire doesn't have a brightness slider that changes the background tint.
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Old 12-17-2011, 01:08 AM   #6
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The eye strain is caused by the background being too bright unlike the stock Kindle Android app the Fire doesn't have a brightness slider that changes the background tint.
It can also be caused by poor SPFR as mentioned earlier.

There's a reason why most OS's that use SPFR also include a utility to 'tune' it so that it matches your display more closely.
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Old 12-17-2011, 08:30 AM   #7
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I might just be drinking the kool-aide on this one,but there appears to be a difference. I've only done a couple hours of reading in normal landscape, but there is definitely less eyestrain. Now this is only with the kindle reading application. Other people may be utilizing another reading application in portrait mode, but to me there is a significant reduction.

I honestly believe that you may have found a major application bug. I've never noticed that it only occurred in the reading application.
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Old 12-17-2011, 09:31 AM   #8
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1. The bug is also present in the regular Android Kindle app. For instance, my Archos 43 minitablet has perfect font rendering in normal portrait (on the Archos display the RGB stripes run horizontally in portrait mode), but shows a bit of the bloom in landscape, only in the Kindle app.

2. As for brightness, I wish rooting weren't illegal! Then it might be an easy fix, just as it is on my Archos 43 ( for users outside the US where rooting without the manufacturer's permission may be legal, you can try my SuperDim app: http://code.google.com/p/superdim )
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Old 12-17-2011, 10:12 AM   #9
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1.
2. As for brightness, I wish rooting weren't illegal! Then it might be an easy fix, just as it is on my Archos 43 ( for users outside the US where rooting without the manufacturer's permission may be legal, you can try my SuperDim app: http://code.google.com/p/superdim )
This is why I keep sending Amazon feedback via the app to put the brightness slider back in. It looks all they did for the Kindle app on the Fire was port it over and make a few changes some good and some bad like removing the brightness slider.

I use Mantano as my reader app and the Screen Filter app to dim the screen at night. Screen Filter is basically a grey layer that lays on top the screen. You can change the transparency which makes the screen look more dim then it really is. It works alright but sometimes out of blue it disables itself causing you to get blinded for a few moments.
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Old 12-17-2011, 12:34 PM   #10
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Screen Filter is no substitute for a proper brightness adjust. A proper brightness adjust lowers backlight intensity, thereby making the blacks be blacker and the whites be grayer. Screen Filter makes the whites be grayer but doesn't make the blacks be blacker, because instead of changing the hardware backlight brightness, it just darkens the pixels in software.

I wonder, though, if there might not be some clever way of doing what Screen Filter does and using the API for changing the backlight within an app on the transparent window that (I think) Screen Filter uses to darken the screen. Hmm. That would allow the same outcome as SuperDim without the need for root.

(Or one could just do what one can to support the EFF proposal for a rooting exception to the DMCA for all devices, not just for phones, and then we could legally root, and all would be easy.)
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Old 12-17-2011, 05:33 PM   #11
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Screen Filter is no substitute for a proper brightness adjust. A proper brightness adjust lowers backlight intensity, thereby making the blacks be blacker and the whites be grayer. Screen Filter makes the whites be grayer but doesn't make the blacks be blacker, because instead of changing the hardware backlight brightness, it just darkens the pixels in software.

I wonder, though, if there might not be some clever way of doing what Screen Filter does and using the API for changing the backlight within an app on the transparent window that (I think) Screen Filter uses to darken the screen. Hmm. That would allow the same outcome as SuperDim without the need for root.

(Or one could just do what one can to support the EFF proposal for a rooting exception to the DMCA for all devices, not just for phones, and then we could legally root, and all would be easy.)
I would love an app that does that. I realize Screen Filter isn't the best but it's the only thing that works on the Fire to dim anything.

The problem with rooting the Fire is Amazon pushes out updates without your permission and so you are taking a risk of bricking the device if you leave it rooted.
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Old 12-17-2011, 06:32 PM   #12
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What are the first 8 digits if your serial number? It appears there may have been a hardware change in the Kindle Fire.

The first one I had which died had all kinds of problems and it's first 8 digits were: D01E B0A0.

The second Fire due to me on this Monday has its first 8 digits as follows: D01E C0A0.

Its very possible that the C0A0 run fixed a lot of hardware problems associated with the B0A0 run.
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Old 12-17-2011, 09:31 PM   #13
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What are the first 8 digits if your serial number? It appears there may have been a hardware change in the Kindle Fire.

The first one I had which died had all kinds of problems and it's first 8 digits were: D01E B0A0.

The second Fire due to me on this Monday has its first 8 digits as follows: D01E C0A0.

Its very possible that the C0A0 run fixed a lot of hardware problems associated with the B0A0 run.
The subpixel stuff is a software problem present both on our Kindle Fire and in the Android Kindle app. It's not a hardware issue.
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Old 12-18-2011, 02:54 PM   #14
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Here are photos taken by putting the Fire under a microscope.

Notice how nice the Landscape letters look with no color shadows. But in all other modes, the results are terrible. The worst of all is reversed landscape (landscape with power button on left): you can see a nasty red shadow on the left of the long vertical of the "h" and a nasty blue shadow on the right. Portrait and reversed portrait aren't quite so terrible, but are pretty bad (and I think especially bad if you turn on night mode and look at white text on a black background). You can see that the portrait and reversed portrait "h" has the red and green subpixels turned on and the blue subpixels muted on the left of the long vertical stroke, which results in an orange shadow. This works perfectly in the landscape "h" where the darkened blue subpixel merges visually into the vertical and the red and green ones merge into the white beside it, and that was the assumption on which the font renderer was working.
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Old 12-18-2011, 05:25 PM   #15
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Here are photos taken by putting the Fire under a microscope.

Notice how nice the Landscape letters look with no color shadows. But in all other modes, the results are terrible. The worst of all is reversed landscape (landscape with power button on left): you can see a nasty red shadow on the left of the long vertical of the "h" and a nasty blue shadow on the right. Portrait and reversed portrait aren't quite so terrible, but are pretty bad (and I think especially bad if you turn on night mode and look at white text on a black background). You can see that the portrait and reversed portrait "h" has the red and green subpixels turned on and the blue subpixels muted on the left of the long vertical stroke, which results in an orange shadow. This works perfectly in the landscape "h" where the darkened blue subpixel merges visually into the vertical and the red and green ones merge into the white beside it, and that was the assumption on which the font renderer was working.
Wow, that is really noticeable when you blow it up like that. I wouldn't be surprised if that really would bother my eyes if I read for very long like that. Oddly enough, this is the first reader I've had that I read almost exclusively in landscape mode, so I haven't noticed any issues. I'm lazy, so I've just been propping it on the arm of the chair or on the nearest cat to read.
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