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Author Topic: Double buffering JPEG stream  (Read 53 times)

nico

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Double buffering JPEG stream
« on: April 10, 2019, 01:42:13 PM »

Hi,
we are displaying a JPEG stream with a resoltion of 800x480 but due to the limited GRAM of 1MB (1 image is already 800*480*2 = 768000 Byte)
we couldn't buffer a second image which leads to a tearing effect.
This happens when the BT815 displays the image while the the new image is overwriting the old one.
Did we miss something? Maybe there is a way to synchronize it?

Best regards,
Nico
« Last Edit: April 12, 2019, 09:04:23 AM by nico »
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Rudolph

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Re: Double buffering JPEG stream
« Reply #1 on: April 12, 2019, 02:10:40 PM »

You could either scale down the .jpg in order to fit two into GRAM and scale them up to 800x480.
Or, with the BT815, it should be possible to use ASTC instead.

I have not tried if this works but chapter 6 in the programming guide states:
"With enough ASTC images in flash memory or RAM_G, it is
possible for user to construct an image-rich GUI application."

COMPRESSED_RGBA_ASTC_4x4_KHR has 8 bits per Pixel, the other formats use less bits per pixel.

At least with the EVE Asset Builder it takes quite some time to convert images to ASTC though.
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nico

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Re: Double buffering JPEG stream
« Reply #2 on: April 15, 2019, 12:40:32 PM »

Hi Rudolph,
thank your for your response. Unfortunately, the BT815 gets a video stream containing jpg images
with 800x480 which cannot be converted to astc beforehand.

Scaling down to a lower resolution would be a solution
but it would decrease the video quality as well which is not an option for us.

Maybe there is an other solution to get a propper result.

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BRT Community

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Re: Double buffering JPEG stream
« Reply #3 on: April 15, 2019, 01:16:46 PM »

Hello,

The core issue here relates to the size limitation of RAM_G.

Rudolph has covered the main options, scaling down the image or using the ASTC image type.

The encoding process for ASTC is quite slow, compared to decoding.
There is a real-time encoder called ASTCRT, (https://github.com/daoo/astcrt). You could try encoding the JPEG stream to ASTC stream on the fly. I may suggest they can use block size 6x6 and veryfast option while encoding.

Best Regards,
BRT Community
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