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Framebuffer 320x240

Posted: Wed Mar 27, 2013 1:42 pm
by muth
Sorry for the duplicate topic, I think I had put in the wrong forum.

I made an interface to connect a custom screen via the HDMI. The screen resolution is 320x240.
The minimum resolution of HDMI is 640x480. Then in config.txt I put

Code: Select all

hdmi_group=2
hdmi_mode=4
framebuffer_width = 320
framebuffer_height = 240
Problem is there is a sort of anti-aliasing applied during the up-scaling between the system 320X240 resolution and the minimun 640x480 HDMI reslution. Making the image blur, and not really exact for my application.

I found there https://github.com/raspberrypi/firmware/issues/104 that

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scaling_kernel=8
#means SCALERLIB_KERNELS_TYPES_NEAREST_NEIGHBOUR 
With HDMI groupe 2, mode 4 (640x480) and framebuffer of 320x240 and scaling_kernel = 8 , nothing is displayed.
But in 800x600 the result is some pixel are used and other not. it seems not really stable by different boot with the same config, some times one over 4 pixel is used, sometimes one over 4 is black.
Image

I submit on the Github an issue, don't know if it's good idea...
https://github.com/raspberrypi/firmware/issues/168

Re: Framebuffer 320x240

Posted: Fri Apr 05, 2013 2:38 pm
by -rst-

Re: Framebuffer 320x240

Posted: Mon Apr 15, 2013 10:18 am
by muth
Thanks a lot !
I'll give a try.