openfpga666 / jpeg-ls_extension

An enhanced version of JPEG-LS extension (ITU-T T.870) image encoder/decoder in C language.

enhanced JPEG-LS extension

An enhanced version of JPEG-LS extension (ITU-T T.870) image encoder/decoder in C language.

Its lossless compression ratio is better than PNG, JPEG2000, WEBP, HEIF, JPEG-LS baseline, and JPEG-LS extension.

　

Why ?

JPEG-LS (JLS) is a lossless/lossy compression standard. There are 2 generations:

• JPEG-LS baseline (ITU-T T.87) [8]
• JPEG-LS extension (ITU-T T.870) [1], which has a higher compression ratio.

The current publicly implementations online are all about JPEG-LS baseline, and none of them supports JPEG-LS extension.

This repo is a enhanced implementation of JPEG-LS extension, which gets a higher compression ratio than original JPEG-LS extension.

Note: due to my modification, this repo is not compatible with the original JPEG-LS extension standard.

　

Development progress

• grey 8 bit lossless image encode/decode
• grey 8 bit lossy (near-lossless) image encode/decode

　

Code list

The code files are in pure-C, located in the src folder:

• JLSx.c : Implement a enhanced JLS extension encode/decode
• JLSx.h : Expose the functions of enhanced JLS extension encode/decode to users.
• JLSxMain.c : A main program with main() function, which call JLSx.h to achieve image file compression/decompression.

　

Compile

Compile in Windows (CMD)

If you add the Microsoft C compiler (cl. exe) of Visual Studio to environment variables, you can compile using the command line (CMD).

cl src\*.c /FeJLSx.exe /Ox

We'll get the executable file JLSx.exe . Here I've compiled it for you, you can use it directly.

Compile in Linux

Run the command in the current directory:

gcc src/*.c -o JLSx -O3 -Wall

We'll get the binary file JLSx . Here I've compiled it for you, you can use it directly.

　

Run image compression/decompression

This program can compress .pgm image file to .jlsxn image file. Or decompress .jlsxn image file to .pgm image file.

Note that .pgm is a simple uncompressed image format (see PGM Image File Specification [2]). PGM file format contains:

• A simple header that contains the width, height, and depth of this image.
• The raw pixel values of this image.

Run in Windows (CMD)

用以下命令把图像文件 1.pgm 压缩为 1.jlsxn 。

Use following command to compress 1.pgm to 1.jlsxn

JLSx.exe 1.pgm 1.jlsxn <near>

Where [near] is a optional parameter of range 0~9 :

• 0 : lossless (default)
• 1~9 : lossy. The larger the near value, the higher distortion and the lower compressed size.

Use following command to compress 1.jlsxn to 1.pgm

JLSx.exe 1.jlsxn 1.pgm

Run in Linux

The command format is similar to Windows. You only need to replace the executable file name with ./JLSx .

　

Evaluating compression ratio

This section presents the results of comparing enhanced JPEG-LS extension (this design) to other lossless image compression formats.

Formats for participating in comparison

The following table shows the formats involved in the comparison and how they were generated. Note that they all operate in lossless compression mode.

Compressed format	Using what software?	options	meaning of options
PNG	OptiPNG [3]	-o7	heaviest compression
JPEG2000	Python Pillow 9.5.0 [4]	irreversible=False	lossless compression
WEBP	Python Pillow 9.5.0 [4]	lossless=True, method=6	lossless heaviest compression
FLIF (now part of JPEG-XL) [5]	FLIF [5]	-N -E100	non-interlaced, heaviest compression
CALIC [6]	CALIC executable file [7]	-	-
JPEG-LS baseline (ITU-T T.87) [8]	Python Pillow-jpls [9]	near=0	lossless compression
JPEG-LS extension (ITU-T T.870) [1]	我按照文档实现，未开源	near=0	lossless compression
enhanced JPEG-LS extension	This repo	near=0	lossless compression

Benchmark

Use the following two image datasets to compare compression ratios.

	small image benchmark	large image benchmark
source	Kodak Image Suite [10]	Gray 8 bit in this website
preprocess	convert RGB to grey 8-bit	needn't
pixel format before compression	grey 8-bit	grey 8-bit
file format before compression	.pgm	.pgm
data volume before compression	9437544 bytes	162870743 bytes
image count	24	15
notes	See img_kodak in this repo	didn't include in this repo. Download it yourself

result of compression ratio

Compress the above two benchmarks and obtain the compression ratio as follows.

Note: Compression ratio=size before compression/size after compression. The larger the better.

Compressed format	small image benchmark	large image benchmark
PNG	1.725	2.202
JPEG2000	1.793	2.309
WEBP	1.847	2.356
FLIF (now part of JPEG-XL)	1.864	2.534 (1st)
CALIC	1.913 (1st)	2.458
JPEG-LS baseline (ITU-T T.87)	1.845	2.333
JPEG-LS extension (ITU-T T.870)	1.884	2.411
enhanced JPEG-LS extension (this repo)	1.911 (2nd)	2.470 (2nd)

　

　

　

Reference

[1] JPEG-LS extension (ITU-T T.870) : https://www.itu.int/rec/T-REC-T.870/en

[2] PGM Image File Specification : https://netpbm.sourceforge.net/doc/pgm.html#index

[3] OptiPNG: Advanced PNG Optimizer : https://optipng.sourceforge.net/

[4] Python Pillow Supported Image file formats : https://pillow.readthedocs.io/en/stable/handbook/image-file-formats.html

[5] FLIF: Free Lossless Image Format : https://github.com/FLIF-hub/FLIF

[6] CALIC paper: Context-based, adaptive, lossless image coding : https://ieeexplore.ieee.org/document/585919/

[7] CALIC executable file : https://www.ece.mcmaster.ca/~xwu/calicexe/

[8] JPEG-LS baseline (ITU-T T.87) : https://www.itu.int/rec/T-REC-T.87/en

[9] pillow-jpls: A JPEG-LS plugin for the Python Pillow library: https://github.com/planetmarshall/pillow-jpls

[10] Kodak Lossless True Color Image Suite : https://r0k.us/graphics/kodak/