Well, thats my point.
What we see in the 2 good Joe Johnston pics may not be what we see on screen as the finished trooper pack.
I believe, based on the two good Joe Johnston pics we have, that the backpack he is wearing in those pictures is not white but light grey.
But, like I said, that might not be what we see on screen.
Looking over Joe's shoulder, I see a round tank with a certain roundover and angle between the sides and the endcap, which I believe matches up with the object sitting in that trench photo. I also see detail on the top of the endcap that seems to match up with the detail on the object in the trench photo.
I believe those 2 items are one in the same.
They might have shot the cannons and troopers as seperate elements and them combined them together, or they might have placed the cannons close to the camera, the troopers far away, and created a forced-perspective and shot all the elements in the same frame to save one more pass through the optical printer.
I also see an object that was built, painted, and as far as I know was never seen on screen in ANH. What is it? If not a Spacetrooper backpack?
What we are missing is the bottom tank that the hose attaches to. It could be sitting down inside the trench and out of frame in that picture.
And after viewing the dailies, they might have gone back and painted it gloss white and re-shot the troopers.
Maybe Chris from POSW could chime in?