display resolution – Ubuntu 18.04 Overscan / Underscan Issues

I use an older flat screen as a monitor. The problem is that this is a TV old enough not to have overscan / underscan options on any port, except for the old VGA / PC port, and I connect via HDMI from an AMD Radeon R9 290x processor. When I activate the sub-scan in the settings, this allows to see the entire image, but underlines it too much, which makes the screen very small and also places lines in it. 39, image, which gives a poor quality for everything and for the text. to be difficult to read. In addition, my TV is a former RCA L26WD26D, which supports a maximum resolution of 1368×768, resolution also recommended by the TV manual for PC connections (that Ubuntu does not allow, for whatever reason, to set in settings, without adding manually to xrandr).

I've done this in the terminal:

cvt 1366 768
# 1368x768 59.88 Hz (CVT) hsync: 47.79 kHz; pclk: 85.25 MHz
Modeline "1368x768_60.00" 85.25 1368 1440 1576 1784 768 771 781 798 -hsync + vsync

xrandr --newmode 1368x768_60.00 85.25 1368 1440 1576 1784 768 771 781 798 -hsync + vsync

xrandr --addmode HDMI-0 1368x768_60.00

I then went to the settings and selected the new resolution. However, it was still being over-analyzed and the activation of the sub-scan in the settings presented the same problem as before. I have therefore launched the following command:

xrandr --output HDMI-0 --set sub-scan on

This corrected the subscanning too much, and the image now exactly matches the size of the screen. However, there are still problems with lines in the image, which makes the text hard to read and all graphics and images have a very bad image. These are horizontal lines, not vertical, and I do not find a way to make them disappear, except to disable the sub-scan, which makes the image too big for the screen.

This is not a problem when I start on Windows on the same computer, even if I use the sub-scan so that the image also adapts to Windows (however, the under -Scan is much easier to work properly under Windows).

At this point, I would connect via VGA or DVI to get a resolution of this problem. Although my TV supports VGA, my graphics card does not allow it and my TV does not have a dedicated DVI input. I've tried using a DVI to HDMI adapter on the TV, but the problem persists. I've also tried using the amdgpu-pro drivers to see if they were handling it better than the open source drivers, but after installation, no images are displayed at the same time. boot and I have to start in recovery mode and run the command "amdgpu-pro -uninstall" in the root terminal for the video to work again, so it's not an option. Any help would be greatly appreciated.