I do not have a file of that size to test with. Smaller files (@ 100mb) convert without issues.
Regarding reducing the number of rows and columns, you can not do this without loss of image quality, as this is a resampling function, and will create cells at a larger size to reduce the row / column of the image.
Is the entire image needed? If you can crop the image, you will retain the original resolution / quality, and reduce the number of rows / columns.
Another possibility is to split the image into more manageable pieces, and then work with those instead of the entire source all at once.
Regards,
Jim