Ad 1) Its funny, because I have been using SUMO longer then 10 years and I've always used UTM decals in metric system without problems (only the origin).
ad 2) Yes, when I change global gamma settings to 0.45, the images looks good, but its not solution for me.
Thanks for support,
Petr
1. SUMO only supports jgw files in WGS84 (so the offset must be something in lon,lat and the pixels size must be in degrees). Your world file contains projected UTM data instead.
2. I cannot replicate the gamma-bias. The loaded image in sumo-gui has the same color as in an image view for me. This might be a graphics driver issue.