Assuming, quite a bit here actually, that the PB150's GSC is the same as the GSC ASIC in the Duo 250, it probably detects the amount of VRAM available on its own.
However, though not certain, it's likely that the LCD is the limiting factor.
Opening it up to get the LCD part# and manufacturer might help in determining that. But then, there's the data path from GSC to the LCD that could be the choke point as well. I don't know much about LCD interfacing and it probably shows, but i thought it was worth mentioning, even long shots win out sometimes.
It's not a new resolution, just two more bits of grayscale depth for the same pixel count.
Actually at a full 640 x 480 x 2bit GS, the 150's resolution is higher than the Duo 250's 640 x 400 x 4bit GS orthe Duo 280's x 640 x 480 x 6bit GS.
However, though not certain, it's likely that the LCD is the limiting factor.
Opening it up to get the LCD part# and manufacturer might help in determining that. But then, there's the data path from GSC to the LCD that could be the choke point as well. I don't know much about LCD interfacing and it probably shows, but i thought it was worth mentioning, even long shots win out sometimes.
It's not a new resolution, just two more bits of grayscale depth for the same pixel count.
Actually at a full 640 x 480 x 2bit GS, the 150's resolution is higher than the Duo 250's 640 x 400 x 4bit GS orthe Duo 280's x 640 x 480 x 6bit GS.