Large imshow images are now downsampled

When showing an image using imshow that has more than \(2^{24}\) columns or \(2^{23}\) rows, the image will now be downsampled to below this resolution before being resampled for display by the AGG renderer. Previously such a large image would be shown incorrectly. To prevent this downsampling and the warning it raises, manually downsample your data before handing it to imshow