Trisquel 8 - Graphic Card Radeon HD

Hi,

I recently installed Trisquel 8 on an old Samsung R522.

All is fine but image or photos are displayed with a bad aspect ratio and they seems to be shrinked.

If I take a look to configuration, the screen has the following resolution 1024x768 61Hz. When my computer use Windows OS, the resolution was more like 1366x768.

If I run the command 'inxi -G', I get :

Graphics:  Card: Advanced Micro Devices [AMD/ATI] RV710/M92 [Mobility Radeon HD 4330/4350/4550]
           Display Server: X.Org 1.18.4 driver: vesa
           Resolution: 1024x768@61.00hz
           GLX Renderer: llvmpipe (LLVM 6.0, 128 bits)
           GLX Version: 3.0 Mesa 18.0.5

If I run the command 'xrand', I get :

xrandr: Failed to get size of gamma for output default
Screen 0: minimum 800 x 600, current 1024 x 768, maximum 1024 x 768
default connected primary 1024x768+0+0 0mm x 0mm
   1024x768      61.00* 
   800x600       61.00  

The "Failed to get size of gamma" is probably not a good thing.

I try to correct the problem by manually install following packages :

firmware-amd-graphics_20161130-5~deb8u1_all.deb 
firmware-misc-nonfree_20161130-5~deb8u1_all.deb 
firmware-linux-nonfree_20161130-5~deb8u1_all.deb 

It does not change anything.

I try to rename the file /etc/X11/xorg.conf.vesa to /etc/X11/xorg.conf.
This modification add the resolution 800x600 but images are still shrinked.

Any idea to solve the problem ?
Thanks in advanced