一种基于字节型多变长码的串匹配的Alpha图像编码算法

doi:10.11959/j.issn.1000-0801.2018285

Abstract

Abstract:

According to the characteristics of Alpha image and the statistical characteristics of coding parameters of string matching algorithm,an Alpha image coding algorithm based on byte-size multi-variable long-length string matching was proposed.The algorithm firstly used a byte-type multi-variable long-code scheme for joint optimization coding of multiple string matching coding parameters,the offset parameter was then encoded using a segmentation mapping scheme with proximity offset prioritization.Finally,the matching string length parameter was matched with a segmentation coding scheme.The experimental results show that compared with LZ4HC,zlib,PNG and HEVC (x265),the proposed algorithm has the advantages of ultra-low complexity and high coding efficiency.

Key words: image coding, Alpha image, variable-length-code, fixed-length-code, string matching

CLC Number:

TN919.81

Liping ZHAO,Tao LIN,Kailun ZHOU,Hua PENG,Keli HU. A byte-size multi-variable-length-code based string matching algorithm for Alpha image coding[J]. Telecommunications Science, 2018, 34(11): 96-104.

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References 16

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语法元素	取值范围	编码方案
未匹配串长度	<15	用标识字节的前4位表示，不再需要额外字节
	≥15	标识字节的前4位为1111，用额外的1~N byte表示长度减去15的部分
未匹配字节数值	0~255	定长码：1 byte
匹配串偏移量	0~65 535	定长码：2 byte
匹配串长度	<15	用标识字节的后4位表示，不再需要额外字节
	≥15	标识字节的后4位为1111，其余的按未匹配串长度的编码方案编码

语法元素	含义	每个类别中的取值说明
T1	未匹配串长度是否为0	第1、2类中T1取值为0（表示为0），第3类中取值为1
T2	Offset是否为1或W	第1类中T2取值为0，第2类中取值为1
T3	Offset是1或W	T3为0表示Offset为1，否则表示Offset为W
T4	Offset是W-1或W+1，或其他值	T4为00表示Offset为W-1，01表示Offset为W+1，10表示Offset≤256（用1字节表示），11表示Offset>256（用2字节表示）

映射前的Offset值	映射后的Offset值
W-6~W+6（12个Offset，不含W）	1~12
2W-1~2W+1（3个Offset）	13~15
W-9~W-7（3个Offset）	2W-1~2W+1
1~W-10	16~W+5
其他值	不变

匹配串长度（ml）的值	分段编码方案
ml<30	用标识字节的最低5 bit表示
30≤ml≤30+255	标识字节的最低5 bit设置为11110，减去30的部分，用1 byte表示
31+255≤ml≤31+255+65 534	标识字节的最低5 bit设置为11111，减去31+255的部分，用2 byte表示
ml≥31+255+65 535	标识字节的后5 bit设置为11111，接着2 byte全设置为1，减去655 665的部分，用表1中LZ4HC
	算法进行编码

编码算法	配置参数
LZ4HC、BMVLC-SM	level 1~level 4
zlib、PNG	fast（level 1）、default（level 6）、slow（level 9）
x265	fast（preset 0）、default（preset 5）、slow（preset 9）

A byte-size multi-variable-length-code based string matching algorithm for Alpha image coding

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BMVLC-SM / LZ4HC	单个序列结果（分辨率：6 614 dpi×5 093 dpi，图2第2行第6幅）					所有序列汇总结果
BMVLC-SM / LZ4HC	level1	level2	level3	level4	平均	level1	level2	level3	level4	平均
压缩码流总字节数比值	55.22%	55.04%	54.93%	54.86%	55.01%	87.56%	88.27%	88.92%	89.38%	88.53%
编码时间比值	95.84%	87.22%	75.42%	61.30%	79.95%	95.32%	88.53%	79.24%	69.25%	83.10%
解码时间比值	100.72%	99.35%	97.71%	98.22%	99.00%	115.14%	118.23%	117.08%	116.81%	116.82%
编码+解码时间比值	96.73%	89.27%89.27%	78.81%	65.89%	82.68%	98.45%	92.86%	84.06%	74.33%	87.42%

	zlib (fast)	zlib (default)	zlib (slow)	PNG (fast)	PNG (default)	PNG (slow)	x265 (fast)	x265 (default)	x265 (slow)
压缩码流总字节数比值	91.69%	114.88%	119.39%	100.97%	131.67%	137.33%	93.89%	137.63%	139.95%
编码时间比值	87.06%	30.45%	10.77%	31.30%	17.18%	4.74%	8.00%	3.49%	3.05%
解码时间比值	21.73%	20.12%	20.34%	18.57%	15.92%	16.19%	1.35%	1.57%	1.57%