enthought
Kiva Quartz backend renders images differently than AGG
The easiest way to reproduce this bug is to create a Chaco image plot and set the orientation to 'v'. When comparing the output of Quartz and AGG, the result will be rotated 180º.
This discrepancy only occurs when the origin is set to 'top left' or 'bottom right'. The AGG result seems to be the correct one: Setting orientation = 'v' simply switches the x- and y-axes, regardless of where the origin is set. In the Quartz result, a value that was at x (y) moves to w - x (h - y) when the origin is set to 'top left' or 'bottom right'.
This may just be a bug in Chaco. In most cases, the rectangle passed to the graphics context is (x0, y0, w, h), where (x0, y0) specifies the lower-left corner. For the case where orientation = v and origin is top left or bottom right, the rectangle is (x1, y1, -w, -h), where (x1, y1) is the upper right corner.