Wardez, I am quite intrigued by this "pixel counting" technique. How in fact is this done (or could you link me to an explanation on how its done)
I capture the image (but if you can take really still camera shots you can get the reference image that way as well) then I load it into Photoshop (any version) and I have the units of measure changed to pixels from the default (usually inches or cm) then open up the information pallette ( you can open this from the drop down "Window" menu in the toolbar).
After that's set up, you can easily get precise pixel measurements using the marquee/selection box tool as the information pallette displays the real time size of selected areas and coordinates as well.
I usually just crop the reference image down so it's just the tire read out, then I zoom in and measure from above the black line toward the bottom of each wear indicator (blue box).
Note: if you capture at a higher resolution or take a photo at any different resolution or distance away from the TV the pixel "size" of the tire indicator will of course vary.
I measure in 720p raw resolution but you can easily change the image size so there are more pixels, more pixels = higher fidelity. Since I'm measuring the raw pixels I only get 20 in my selection box when measuring a full tire, so I can only get a percentage of 20. So I'm limited to factors of 5 e.g. 45% 50% 55% and so on, but I really don't see a need for it to be tighter than that since on the in-game indicator it can't drop less than a pixel at a time anyway, so the game's also limited by the same step-frequency.
I'll start the area selection from the bottom of the tire and drag it up to get a measurement, and I'll use the selection transformation tool (right click selection > transform selection) to get an exact precise measurement if I need to.
I'll get my number of pixels e.g. 15. Then use that to determine the wear percenatge based against our new tire reference pixel number of 20.
Percentage =(15/20)*100
15 divided by twenty is .75
.75 times 100 is 75.
The tire has worn by 25% with 75% remaining.