Create a sparse disk image from a given device. Used on Linux.

sparse_dd.py

#!/usr/bin/env python3
import os
import sys

BLOCK_SIZE = 4096  # 4 KB

def is_zero_block(block):
    return block == b'\x00' * len(block)

def sparse_copy(src_path, dst_path):
    with open(src_path, 'rb') as src, open(dst_path, 'wb') as dst:
        while True:
            block = src.read(BLOCK_SIZE)
            if not block:
                break
            if is_zero_block(block):
                dst.seek(BLOCK_SIZE, os.SEEK_CUR)
            else:
                dst.write(block)

if __name__ == "__main__":
    if len(sys.argv) != 3:
        print(f"Usage: {sys.argv[0]} /dev/sdX output.img", file=sys.stderr)
        sys.exit(1)

    sparse_copy(sys.argv[1], sys.argv[2])

To write the sparse image back to a device/drive/sdcard:

sudo dd if=sdcard.sparse.raw of=/dev/sdX bs=4M status=progress