Which camera are you using? The camera file determines the scan direction for a particular camera, not the API, and this is fixed for a given camera. For most single tap cameras this will be upper/left to lower/right. Multiple tap cameras use a variety of scanning methods for pixel arrangement. If you would like the image to have a different orientation, use IMAQ Symmetry and IMAQ Rotate to rearrange the image.
Regards,
Brent R.
Applications Engineer
National Instruments
