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Video output different than LCD

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Offline achillies

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Video output different than LCD
« on: 10 / May / 2011, 09:50:54 »
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This is rather hard to describe, so I posted a few youtube videos for clarity.

I have an SX130IS.  I am testing SDM for this camera, specifically inverted playback.  When viewing the LCD with inverted playback enabled, the image is not inverted, and often the LCD output is garbage.  When I connect a video cable to view the output externally, even though they are not quite correct, the images are inverted and the display is different (than with the LCD).  Is there a different buffer for the video output?

youtube LCD dislpay -> http://www.youtube.com/watch?v=DmSJUI8Tzp4#
youtube video output -> http://www.youtube.com/watch?v=DHZrbDMcrYE#

If this is not clear (or in the wrong thread), please let me know.
Don't let the sands of time get in your lunch.

Re: Video output different than LCD
« Reply #1 on: 12 / May / 2011, 17:31:42 »
My wild guess at the moment is that it has to do with timing.

From what I've seen it seems to be that to actually really draw the image the firmware writes the buffer address and some other info to special addresses. I guess this signals a special chip to do the drawing using the new info. If this is the case, the drawing happens in parallel with whatever the firmware/CHDK/SDM is doing.

Perhaps that this camera, in contrast to others, only draws the image once when it is explicitly updated instead of every x ms? And contrary to the display the video output is updated late enough that you have time to change the buffer?

One part of your video that supports these ideas is the moment you first switch to playback mode in the second video (0:53). There the top of the image is still normal while the rest is flipped. As if the memcpy of your invert function (or perhaps as cache write?) catched up with the drawing.

I would experiment with this. Delay inverting the image. Increase a number every time invert is called and constantly draw it to the buffer (or just draw a "blinking" block). Etc.

The border at the left is possibly due to the buffer being wider than the image (i.e. every row is padded with some extra bytes). It's still odd, because when it has part of the original image, it suggest the padding is made of transparent pixels (or at least some YUV combo is interpreted as transparent). The flipped image does seem cropped at the right.

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Offline achillies

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Re: Video output different than LCD
« Reply #2 on: 13 / May / 2011, 09:39:57 »
Thank you for taking the time to review and comment.  This camera (SX130IS) really seems to have some differences compared to others, and those differences are sometimes hard to find.

Playback buffers seem to be trouble, but hopefully with time (and help), it will all be sorted out.
Don't let the sands of time get in your lunch.

 

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