genlzwtest.bash

Date de création 2022-09-05

Date d’expiration 2022-12-07

#!/bin/bash

function get_value32() {
    local source_file="$1"
    local offset="$2"
    od \
        --skip-bytes="$offset" \
        --read-bytes=4 \
        --endian=little \
        --format=d4 \
        --address-radix=n \
        "$source_file"
}

function extract_bytes() {
    local source_file="$1"
    local offset="$2"
    local length="$3"

dd \
        skip="$offset" \
        count="$length" \
        bs=1 \
        if="$source_file"
}

if ! command -v convert &> /dev/null
then
    echo "Image Magick is not installed" >&2
    exit 1
fi

convert \
    -set colorspace Gray \
    -depth 8 \
    -pointsize 6 \
    label:D \
    GRAY:lzw_test.uncompressed

convert \
    -set colorspace Gray \
    -depth 8 \
    -pointsize 6 \
    label:D \
    -compress lzw \
    lzw_test.tiff

image_file_directory_offset=$(get_value32 lzw_test.tiff 4)
compressed_stream_length=$((image_file_directory_offset - 8))
extract_bytes lzw_test.tiff 8 "$compressed_stream_length" \
    2> /dev/null \
    > lzw_test.compressed