As you already discovered, the chop works at the opposite of what you need. You select a cross to remove from an image and the remaining areas are glued together in a new image.
I drew to pictures to better explain what I mean:
you select the red area,
the red and yellow areas are removed
the remaining green parts are drawn toward the center and glued together.
If you select a corner, you will observe exactly the behaviour you described (area color meanings are the same of the picture above):
To select a rectangular surface of an image, mainly to get sprites from a spritesheet, you need to use the pygame.Surface.subsurface method. It define a child image of your main one ready to be blitted on a new surface or used as is.
Warning Changes to the main surface or to the subsurface will be reflected on the other one.
As you already discovered, the chop works at the opposite of what you need. You select a cross to remove from an image and the remaining areas are glued together in a new image.
I drew to pictures to better explain what I mean:
If you select a corner, you will observe exactly the behaviour you described (area color meanings are the same of the picture above):
To select a rectangular surface of an image, mainly to get sprites from a spritesheet, you need to use the pygame.Surface.subsurface method. It define a child image of your main one ready to be blitted on a new surface or used as is.
Warning Changes to the main surface or to the subsurface will be reflected on the other one.
thanks for the explanation!