Crop parameters for batch transformations

[bamendt]

I would like to batch convert JPG files and crop them to a specific size with the cropped portion of the image coming from the center of the image. When I input Width and Height parameters, the image is cropped starting in the upper left corner.

For example, I want to batch crop all images to 800 x 600:
Original image is 600 x 1000: crop 100 from top and 100 from bottom
Original image is 600 x 1200: crop 200 from top and 200 from bottom
Original image is 1000 x 1000: crop 100 from left, 100 from right, 200 from top, and 200 from bottom

How do I set the Crop parameters to do this for a batch transformation?

[bamendt]

My example had the wrong values. Corrected values are:
Original image is 600 x 1000: crop 200 from top and 200 from bottom
Original image is 600 x 1200: crop 300 from top and 300 from bottom
Original image is 1000 x 1000: crop 100 from left, 100 from right, 200 from top, and 200 from bottom

[xnview]

My example had the wrong values. Corrected values are:
Original image is 600 x 1000: crop 200 from top and 200 from bottom
Original image is 600 x 1200: crop 300 from top and 300 from bottom
Original image is 1000 x 1000: crop 100 from left, 100 from right, 200 from top, and 200 from bottom

Perhaps you can use canvas resize for that...

[bamendt]

Resize canvas worked for this task. Thank you!