# Whole-Pixel Image Shift

As described in the overview of calibration, the physical and optical configuration you use to acquire the calibration image must be identical to the configuration you use to acquire the run-time image. Additionally, any post-acquisition image processing must be applied identically to both the calibration and run-time images.

The Checkerboard calibration tool performs a check at run-time to verify that the second requirement is met. It performs this check by verifying that the mapping from the selected space of the run-time image to that image's pixel space (# space) is identical to the corresponding mapping in the calibration image.

There is one case in which the Checkerboard calibration tool can still operate correctly if these two transformations are not the same. If the run-time image has undergone a whole-pixel shift, and if this shift is recorded in the root-to-pixel transformation within the image's space tree (@ space to # space), then the Checkerboard calibration tool will work correctly.

This type of whole-pixel shift can be introduced by certain image processing operations and by acquiring images from a line-scan or digital camera using a smaller region of interest (ROI) than was used to acquire the calibration image.

Note: The run-time image can be smaller than the calibration image only if you have specified a WarpDestinationRectangle. In all cases, the run-time image must contain enough pixels to compute values for all pixels in the output image.