First question:
You are probably saving your images in a 'lossy' format (.jpg for example). Use a 'lossless' file format (.png for example) and the dots will go away.
Also note that a black pixel such as (1,0,0) or (3,3,3) is not masked out of an image if the mask color is set to 'true' black (0,0,0).
Second question:
Who cares. Break the image up into smaller images (5,10, etc.) and then load them individually. It's better memory management anyways.
You are probably saving your images in a 'lossy' format (.jpg for example). Use a 'lossless' file format (.png for example) and the dots will go away.
Also note that a black pixel such as (1,0,0) or (3,3,3) is not masked out of an image if the mask color is set to 'true' black (0,0,0).
Second question:
Who cares. Break the image up into smaller images (5,10, etc.) and then load them individually. It's better memory management anyways.