How to clone an SD card with a bootable Linux OS on it?

Question

linux

Please explain how distribution developers, for example, on orangepi.org make images of 300Mb, 1500Mb, 2500Mb in size, that is, smaller than the size of SD cards.
I have written such an image to the card, made some changes in the system and now I want to copy this SD card. The weight of the system has not changed much. dd or Win32 copy the system according to the size of the memory card, if I have a size of 64GB, then the image will be 64GB.
As I understand it depends on the size of the partitions. 16MB FAT32 for kernel everything else for rootfs & home. How can I copy a 3.5GB system on a 64GB stick into an image with the same (3.5GB) size?
I hope I explained well,
thanks

Answer 1

I do this with kpartx .
that's it, you have the fake_blockdevice.img file of the required size, which can be uploaded to the sd card via dd