How to read image lazy?

[magick]

• My image is very big and doesn't fit in memory. I want to read and process it by parts. Is there any way to do it?

Several. You can read the image exclusively from disk:

• convert -limit area 1 bigassimage.tif image.jpg

Of if its raw you can crop part of the image are read time:

• convert -size 32000x32000 'image.rgb[1000x1000+100+100]' image.png

Or use the stream program. See http://www.imagemagick.org/Usage/files/#massive.