ImageMagick:PNG的无损最大压缩？

Question

我想使用ImageMagick保存到无损PNG时达到最大压缩量.我正在批量转换许多PSD.

我尝试了一些东西,但它看起来像我生成的PNG图像不像原始图像那样清晰,尽管我的妻子看不到它.

这些是我正在玩的当前论点:

convert -depth 24 -define png:compression-filter=1 \ 
  -define png:compression-level=9 -define png:compression-strategy=2 

根据:http: //www.imagemagick.org/script/command-line-options.php#define

和http://www.w3.org/TR/PNG-Filters.html

这意味着:

• 压缩过滤器是1(Sub)
• 最大压缩等级9
• 压缩策略是2 huffman_only(所以没有过滤,虽然这个压缩过滤器应该是无损的)

根据文档:"有效值为0到4,表示默认,过滤,huffman_only,rle和固定的ZLIB压缩策略.如果您使用的旧zlib不支持Z_RLE(1.2.0之前)或Z_FIXED(之前) 1.2.2.2),值3和4分别使用zlib默认策略."

顺便说一句,我的图像是960x720像素.

(如果我使用默认压缩策略0,我会得到大文件.可能是9的压缩过滤器和0的压缩策略产生较小尺寸的图像,但我仍然不确定它是否是无损的).

问题:

1. 这是无损压缩吗？如果没有,错误在哪里？
2. 知道如何实现更好的无损压缩吗？

Answer 1

I think you are at, or beyond, the limits of the ImageMagick documentation and would like to suggest you work out your answer empirically - or if you do get a definitive answer, that you at least test it empirically.

I don't have access to your images, so I generated a reference image myself, as follows. It contains a readily compressible block of solid colour (red), a black-white gradient and a bunch of noise, so there is something to make most types of compression happy or unhappy in there.

为了测试你是否有无损压缩,我建议你将图像转换为PPM格式 - 见这里.除了纯粹的图像数据和大小之外,它不包含日期,时间或统计数据或任何其他内容,因此可以比较像素值是否通过压缩而改变.

然后我写了一个脚本如下压缩参考图像使用所有可能的过滤器,策略和级别来查看文件大小,如果他们遭受任何损失,因此不同于参考PPM图像:

这是脚本:

#!/bin/bash
convert -depth 24 -size 200x200 xc:red gradient:black-white \( xc:white +noise random \) +append reference.png
convert reference.png reference.ppm
for f in {0..5}; do
   for l in {0..9}; do
      for s in {0..4}; do
         outfile="out_${f}_${l}_${s}.png"
         convert reference.png -define png:compression-filter=$f -define png:compression-level=$l -define png:compression-strategy=$s "$outfile"
         size=$(OSXFileSize "$outfile")
         echo filter:$f, level:$l, strategy:$s, size:$size
         convert "$outfile" "$outfile.ppm"
         diff "$outfile.ppm" reference.ppm
      done
   done
done

所有文件都进行了相同的比较,因此我使用的任何参数似乎都没有任何压缩损失.尺寸如下:

filter:0, level:0, strategy:0, size:720796
filter:0, level:0, strategy:1, size:720796
filter:0, level:0, strategy:2, size:720801
filter:0, level:0, strategy:3, size:718136
filter:0, level:0, strategy:4, size:720796
filter:0, level:1, strategy:0, size:246377
filter:0, level:1, strategy:1, size:246377
filter:0, level:1, strategy:2, size:524864
filter:0, level:1, strategy:3, size:517549
filter:0, level:1, strategy:4, size:259348
filter:0, level:2, strategy:0, size:246377
filter:0, level:2, strategy:1, size:246377
filter:0, level:2, strategy:2, size:524864
filter:0, level:2, strategy:3, size:517549
filter:0, level:2, strategy:4, size:259348
filter:0, level:3, strategy:0, size:246377
filter:0, level:3, strategy:1, size:246377
filter:0, level:3, strategy:2, size:524864
filter:0, level:3, strategy:3, size:517549
filter:0, level:3, strategy:4, size:259348
filter:0, level:4, strategy:0, size:244894
filter:0, level:4, strategy:1, size:244859
filter:0, level:4, strategy:2, size:524864
filter:0, level:4, strategy:3, size:517549
filter:0, level:4, strategy:4, size:258039
filter:0, level:5, strategy:0, size:244916
filter:0, level:5, strategy:1, size:244881
filter:0, level:5, strategy:2, size:524864
filter:0, level:5, strategy:3, size:517549
filter:0, level:5, strategy:4, size:258064
filter:0, level:6, strategy:0, size:244916
filter:0, level:6, strategy:1, size:244881
filter:0, level:6, strategy:2, size:524864
filter:0, level:6, strategy:3, size:517549
filter:0, level:6, strategy:4, size:258064
filter:0, level:7, strategy:0, size:244916
filter:0, level:7, strategy:1, size:244881
filter:0, level:7, strategy:2, size:524864
filter:0, level:7, strategy:3, size:517549
filter:0, level:7, strategy:4, size:258064
filter:0, level:8, strategy:0, size:244433
filter:0, level:8, strategy:1, size:244405
filter:0, level:8, strategy:2, size:524864
filter:0, level:8, strategy:3, size:517549
filter:0, level:8, strategy:4, size:257674
filter:0, level:9, strategy:0, size:244433
filter:0, level:9, strategy:1, size:244405
filter:0, level:9, strategy:2, size:524864
filter:0, level:9, strategy:3, size:517549
filter:0, level:9, strategy:4, size:257674
filter:1, level:0, strategy:0, size:720796
filter:1, level:0, strategy:1, size:720796
filter:1, level:0, strategy:2, size:720801
filter:1, level:0, strategy:3, size:286904
filter:1, level:0, strategy:4, size:720796
filter:1, level:1, strategy:0, size:247643
filter:1, level:1, strategy:1, size:247643
filter:1, level:1, strategy:2, size:331829
filter:1, level:1, strategy:3, size:245708
filter:1, level:1, strategy:4, size:260505
filter:1, level:2, strategy:0, size:247375
filter:1, level:2, strategy:1, size:247375
filter:1, level:2, strategy:2, size:331829
filter:1, level:2, strategy:3, size:245708
filter:1, level:2, strategy:4, size:260452
filter:1, level:3, strategy:0, size:247375
filter:1, level:3, strategy:1, size:247375
filter:1, level:3, strategy:2, size:331829
filter:1, level:3, strategy:3, size:245708
filter:1, level:3, strategy:4, size:260452
filter:1, level:4, strategy:0, size:245515
filter:1, level:4, strategy:1, size:245489
filter:1, level:4, strategy:2, size:331829
filter:1, level:4, strategy:3, size:245708
filter:1, level:4, strategy:4, size:258810
filter:1, level:5, strategy:0, size:245544
filter:1, level:5, strategy:1, size:245519
filter:1, level:5, strategy:2, size:331829
filter:1, level:5, strategy:3, size:245708
filter:1, level:5, strategy:4, size:258835
filter:1, level:6, strategy:0, size:245597
filter:1, level:6, strategy:1, size:245570
filter:1, level:6, strategy:2, size:331829
filter:1, level:6, strategy:3, size:245708
filter:1, level:6, strategy:4, size:258885
filter:1, level:7, strategy:0, size:245597
filter:1, level:7, strategy:1, size:245570
filter:1, level:7, strategy:2, size:331829
filter:1, level:7, strategy:3, size:245708
filter:1, level:7, strategy:4, size:258885
filter:1, level:8, strategy:0, size:245251
filter:1, level:8, strategy:1, size:245230
filter:1, level:8, strategy:2, size:331829
filter:1, level:8, strategy:3, size:245708
filter:1, level:8, strategy:4, size:258587
filter:1, level:9, strategy:0, size:245267
filter:1, level:9, strategy:1, size:245254
filter:1, level:9, strategy:2, size:331829
filter:1, level:9, strategy:3, size:245708
filter:1, level:9, strategy:4, size:258589
filter:2, level:0, strategy:0, size:720796
filter:2, level:0, strategy:1, size:720796
filter:2, level:0, strategy:2, size:720801
filter:2, level:0, strategy:3, size:628470
filter:2, level:0, strategy:4, size:720796
filter:2, level:1, strategy:0, size:246114
filter:2, level:1, strategy:1, size:246114
filter:2, level:1, strategy:2, size:439545
filter:2, level:1, strategy:3, size:358177
filter:2, level:1, strategy:4, size:258999
filter:2, level:2, strategy:0, size:246114
filter:2, level:2, strategy:1, size:246114
filter:2, level:2, strategy:2, size:439545
filter:2, level:2, strategy:3, size:358177
filter:2, level:2, strategy:4, size:258999
filter:2, level:3, strategy:0, size:246114
filter:2, level:3, strategy:1, size:246114
filter:2, level:3, strategy:2, size:439545
filter:2, level:3, strategy:3, size:358177
filter:2, level:3, strategy:4, size:258999
filter:2, level:4, strategy:0, size:244701
filter:2, level:4, strategy:1, size:244679
filter:2, level:4, strategy:2, size:439545
filter:2, level:4, strategy:3, size:358177
filter:2, level:4, strategy:4, size:257722
filter:2, level:5, strategy:0, size:244721
filter:2, level:5, strategy:1, size:244700
filter:2, level:5, strategy:2, size:439545
filter:2, level:5, strategy:3, size:358177
filter:2, level:5, strategy:4, size:257744
filter:2, level:6, strategy:0, size:244727
filter:2, level:6, strategy:1, size:244704
filter:2, level:6, strategy:2, size:439545
filter:2, level:6, strategy:3, size:358177
filter:2, level:6, strategy:4, size:257744
filter:2, level:7, strategy:0, size:244727
filter:2, level:7, strategy:1, size:244704
filter:2, level:7, strategy:2, size:439545
filter:2, level:7, strategy:3, size:358177
filter:2, level:7, strategy:4, size:257744
filter:2, level:8, strategy:0, size:244340
filter:2, level:8, strategy:1, size:244322
filter:2, level:8, strategy:2, size:439545
filter:2, level:8, strategy:3, size:358177
filter:2, level:8, strategy:4, size:257436
filter:2, level:9, strategy:0, size:244155
filter:2, level:9, strategy:1, size:244130
filter:2, level:9, strategy:2, size:439545
filter:2, level:9, strategy:3, size:358177
filter:2, level:9, strategy:4, size:257298
filter:3, level:0, strategy:0, size:720796
filter:3, level:0, strategy:1, size:720796
filter:3, level:0, strategy:2, size:720801
filter:3, level:0, strategy:3, size:600694
filter:3, level:0, strategy:4, size:720796
filter:3, level:1, strategy:0, size:247741
filter:3, level:1, strategy:1, size:247741
filter:3, level:1, strategy:2, size:429487
filter:3, level:1, strategy:3, size:346943
filter:3, level:1, strategy:4, size:260468
filter:3, level:2, strategy:0, size:247711
filter:3, level:2, strategy:1, size:247711
filter:3, level:2, strategy:2, size:429487
filter:3, level:2, strategy:3, size:346943
filter:3, level:2, strategy:4, size:260444
filter:3, level:3, strategy:0, size:247463
filter:3, level:3, strategy:1, size:247463
filter:3, level:3, strategy:2, size:429487
filter:3, level:3, strategy:3, size:346943
filter:3, level:3, strategy:4, size:260331
filter:3, level:4, strategy:0, size:245681
filter:3, level:4, strategy:1, size:245659
filter:3, level:4, strategy:2, size:429487
filter:3, level:4, strategy:3, size:346943
filter:3, level:4, strategy:4, size:258797
filter:3, level:5, strategy:0, size:245685
filter:3, level:5, strategy:1, size:245663
filter:3, level:5, strategy:2, size:429487
filter:3, level:5, strategy:3, size:346943
filter:3, level:5, strategy:4, size:258796
filter:3, level:6, strategy:0, size:245686
filter:3, level:6, strategy:1, size:245665
filter:3, level:6, strategy:2, size:429487
filter:3, level:6, strategy:3, size:346943
filter:3, level:6, strategy:4, size:258796
filter:3, level:7, strategy:0, size:245686
filter:3, level:7, strategy:1, size:245665
filter:3, level:7, strategy:2, size:429487
filter:3, level:7, strategy:3, size:346943
filter:3, level:7, strategy:4, size:258796
filter:3, level:8, strategy:0, size:245474
filter:3, level:8, strategy:1, size:245458
filter:3, level:8, strategy:2, size:429487
filter:3, level:8, strategy:3, size:346943
filter:3, level:8, strategy:4, size:258628
filter:3, level:9, strategy:0, size:245508
filter:3, level:9, strategy:1, size:245491
filter:3, level:9, strategy:2, size:429487
filter:3, level:9, strategy:3, size:346943
filter:3, level:9, strategy:4, size:258639
filter:4, level:0, strategy:0, size:720796
filter:4, level:0, strategy:1, size:720796
filter:4, level:0, strategy:2, size:720801
filter:4, level:0, strategy:3, size:284043
filter:4, level:0, strategy:4, size:720796
filter:4, level:1, strategy:0, size:246892
filter:4, level:1, strategy:1, size:246892
filter:4, level:1, strategy:2, size:331489
filter:4, level:1, strategy:3, size:245305
filter:4, level:1, strategy:4, size:259428
filter:4, level:2, strategy:0, size:246299
filter:4, level:2, strategy:1, size:246299
filter:4, level:2, strategy:2, size:331489
filter:4, level:2, strategy:3, size:245305
filter:4, level:2, strategy:4, size:259021
filter:4, level:3, strategy:0, size:246316
filter:4, level:3, strategy:1, size:246316
filter:4, level:3, strategy:2, size:331489
filter:4, level:3, strategy:3, size:245305
filter:4, level:3, strategy:4, size:259026
filter:4, level:4, strategy:0, size:244335
filter:4, level:4, strategy:1, size:244259
filter:4, level:4, strategy:2, size:331489
filter:4, level:4, strategy:3, size:245305
filter:4, level:4, strategy:4, size:257491
filter:4, level:5, strategy:0, size:244343
filter:4, level:5, strategy:1, size:244260
filter:4, level:5, strategy:2, size:331489
filter:4, level:5, strategy:3, size:245305
filter:4, level:5, strategy:4, size:257494
filter:4, level:6, strategy:0, size:244350
filter:4, level:6, strategy:1, size:244262
filter:4, level:6, strategy:2, size:331489
filter:4, level:6, strategy:3, size:245305
filter:4, level:6, strategy:4, size:257500
filter:4, level:7, strategy:0, size:244350
filter:4, level:7, strategy:1, size:244262
filter:4, level:7, strategy:2, size:331489
filter:4, level:7, strategy:3, size:245305
filter:4, level:7, strategy:4, size:257500
filter:4, level:8, strategy:0, size:244282
filter:4, level:8, strategy:1, size:244251
filter:4, level:8, strategy:2, size:331489
filter:4, level:8, strategy:3, size:245305
filter:4, level:8, strategy:4, size:257461
filter:4, level:9, strategy:0, size:244321
filter:4, level:9, strategy:1, size:244284
filter:4, level:9, strategy:2, size:331489
filter:4, level:9, strategy:3, size:245305
filter:4, level:9, strategy:4, size:257473
filter:5, level:0, strategy:0, size:720796
filter:5, level:0, strategy:1, size:720796
filter:5, level:0, strategy:2, size:720801
filter:5, level:0, strategy:3, size:287526
filter:5, level:0, strategy:4, size:720796
filter:5, level:1, strategy:0, size:247117
filter:5, level:1, strategy:1, size:247117
filter:5, level:1, strategy:2, size:331910
filter:5, level:1, strategy:3, size:246241
filter:5, level:1, strategy:4, size:259811
filter:5, level:2, strategy:0, size:246903
filter:5, level:2, strategy:1, size:246903
filter:5, level:2, strategy:2, size:331910
filter:5, level:2, strategy:3, size:246241
filter:5, level:2, strategy:4, size:259757
filter:5, level:3, strategy:0, size:246976
filter:5, level:3, strategy:1, size:246976
filter:5, level:3, strategy:2, size:331910
filter:5, level:3, strategy:3, size:246241
filter:5, level:3, strategy:4, size:259742
filter:5, level:4, strategy:0, size:245005
filter:5, level:4, strategy:1, size:244969
filter:5, level:4, strategy:2, size:331910
filter:5, level:4, strategy:3, size:246241
filter:5, level:4, strategy:4, size:258135
filter:5, level:5, strategy:0, size:245025
filter:5, level:5, strategy:1, size:244985
filter:5, level:5, strategy:2, size:331910
filter:5, level:5, strategy:3, size:246241
filter:5, level:5, strategy:4, size:258149
filter:5, level:6, strategy:0, size:245056
filter:5, level:6, strategy:1, size:245009
filter:5, level:6, strategy:2, size:331910
filter:5, level:6, strategy:3, size:246241
filter:5, level:6, strategy:4, size:258176
filter:5, level:7, strategy:0, size:245056
filter:5, level:7, strategy:1, size:245009
filter:5, level:7, strategy:2, size:331910
filter:5, level:7, strategy:3, size:246241
filter:5, level:7, strategy:4, size:258176
filter:5, level:8, strategy:0, size:244838
filter:5, level:8, strategy:1, size:244841
filter:5, level:8, strategy:2, size:331910
filter:5, level:8, strategy:3, size:246241
filter:5, level:8, strategy:4, size:258009
filter:5, level:9, strategy:0, size:244857
filter:5, level:9, strategy:1, size:244857
filter:5, level:9, strategy:2, size:331910
filter:5, level:9, strategy:3, size:246241
filter:5, level:9, strategy:4, size:258009

显然你的数字会有所不同,因为你的图像不同,所以你必须看看什么对你的数据有用 - 但希望这将是一个起点.

请注意,如果按大小对上面的内容进行排序,我会得到:

filter:2, level:9, strategy:1, size:244127
filter:2, level:9, strategy:0, size:244156
filter:4, level:8, strategy:1, size:244251
filter:4, level:4, strategy:1, size:244258
filter:4, level:5, strategy:1, size:244260
filter:4, level:6, strategy:1, size:244262
filter:4, level:7, strategy:1, size:244262
filter:4, level:8, strategy:0, size:244283
filter:4, level:9, strategy:1, size:244285
filter:2, level:8, strategy:1, size:244319
filter:4, level:9, strategy:0, size:244321
filter:4, level:4, strategy:0, size:244333
filter:2, level:8, strategy:0, size:244341
filter:4, level:5, strategy:0, size:244341
filter:4, level:6, strategy:0, size:244350
filter:4, level:7, strategy:0, size:244350
filter:0, level:8, strategy:1, size:244408
filter:0, level:9, strategy:1, size:244408
filter:0, level:8, strategy:0, size:244442
filter:0, level:9, strategy:0, size:244442
filter:2, level:4, strategy:1, size:244677
filter:2, level:5, strategy:1, size:244699
filter:2, level:4, strategy:0, size:244701
filter:2, level:6, strategy:1, size:244704
filter:2, level:7, strategy:1, size:244704
filter:2, level:5, strategy:0, size:244723
filter:2, level:6, strategy:0, size:244729
filter:2, level:7, strategy:0, size:244729
filter:5, level:8, strategy:1, size:244813
filter:5, level:8, strategy:0, size:244822
filter:5, level:9, strategy:1, size:244840
filter:5, level:9, strategy:0, size:244853
filter:0, level:4, strategy:1, size:244860
filter:0, level:5, strategy:1, size:244885
filter:0, level:6, strategy:1, size:244885
filter:0, level:7, strategy:1, size:244885
filter:0, level:4, strategy:0, size:244897
filter:0, level:5, strategy:0, size:244922
filter:0, level:6, strategy:0, size:244922
filter:0, level:7, strategy:0, size:244922
filter:5, level:4, strategy:1, size:244940
filter:5, level:5, strategy:1, size:244956
filter:5, level:6, strategy:1, size:244980
filter:5, level:7, strategy:1, size:244980
filter:5, level:4, strategy:0, size:244982
filter:5, level:5, strategy:0, size:245000
filter:5, level:6, strategy:0, size:245030
filter:5, level:7, strategy:0, size:245030
filter:1, level:8, strategy:1, size:245243
filter:1, level:9, strategy:1, size:245245
filter:1, level:8, strategy:0, size:245267
filter:1, level:9, strategy:0, size:245270
filter:4, level:1, strategy:3, size:245307
filter:4, level:2, strategy:3, size:245307
filter:4, level:3, strategy:3, size:245307
filter:4, level:4, strategy:3, size:245307
filter:4, level:5, strategy:3, size:245307
filter:4, level:6, strategy:3, size:245307
filter:4, level:7, strategy:3, size:245307
filter:4, level:8, strategy:3, size:245307
filter:4, level:9, strategy:3, size:245307
filter:3, level:8, strategy:1, size:245460
filter:5, level:1, strategy:3, size:245469
filter:5, level:2, strategy:3, size:245469
filter:5, level:3, strategy:3, size:245469
filter:5, level:4, strategy:3, size:245469
filter:5, level:5, strategy:3, size:245469
filter:5, level:6, strategy:3, size:245469
filter:5, level:7, strategy:3, size:245469
filter:5, level:8, strategy:3, size:245469
filter:5, level:9, strategy:3, size:245469
filter:3, level:8, strategy:0, size:245487
filter:3, level:9, strategy:1, size:245493
filter:1, level:4, strategy:1, size:245503
filter:3, level:9, strategy:0, size:245521
filter:1, level:4, strategy:0, size:245529
filter:1, level:5, strategy:1, size:245533
filter:1, level:5, strategy:0, size:245559
filter:1, level:6, strategy:1, size:245584
filter:1, level:7, strategy:1, size:245584
filter:1, level:6, strategy:0, size:245606
filter:1, level:7, strategy:0, size:245606
filter:3, level:4, strategy:1, size:245663
filter:3, level:5, strategy:1, size:245668
filter:3, level:6, strategy:1, size:245669
filter:3, level:7, strategy:1, size:245669
filter:3, level:4, strategy:0, size:245696
filter:3, level:5, strategy:0, size:245700
filter:3, level:6, strategy:0, size:245701
filter:3, level:7, strategy:0, size:245701
filter:1, level:1, strategy:3, size:245704
filter:1, level:2, strategy:3, size:245704
filter:1, level:3, strategy:3, size:245704
filter:1, level:4, strategy:3, size:245704
filter:1, level:5, strategy:3, size:245704
filter:1, level:6, strategy:3, size:245704
filter:1, level:7, strategy:3, size:245704
filter:1, level:8, strategy:3, size:245704
filter:1, level:9, strategy:3, size:245704
filter:2, level:1, strategy:0, size:245967
filter:2, level:1, strategy:1, size:245967
filter:2, level:2, strategy:0, size:245967
filter:2, level:2, strategy:1, size:245967
filter:2, level:3, strategy:0, size:245967
filter:2, level:3, strategy:1, size:245967
filter:4, level:2, strategy:0, size:246294
filter:4, level:2, strategy:1, size:246294
filter:4, level:3, strategy:0, size:246309
filter:4, level:3, strategy:1, size:246309
filter:0, level:1, strategy:0, size:246391
filter:0, level:1, strategy:1, size:246391
filter:0, level:2, strategy:0, size:246391
filter:0, level:2, strategy:1, size:246391
filter:0, level:3, strategy:0, size:246391
filter:0, level:3, strategy:1, size:246391
filter:4, level:1, strategy:0, size:246407
filter:4, level:1, strategy:1, size:246407
filter:5, level:2, strategy:0, size:246920
filter:5, level:2, strategy:1, size:246920
filter:5, level:1, strategy:0, size:246926
filter:5, level:1, strategy:1, size:246926
filter:5, level:3, strategy:0, size:246955
filter:5, level:3, strategy:1, size:246955
filter:1, level:2, strategy:0, size:247380
filter:1, level:2, strategy:1, size:247380
filter:1, level:3, strategy:0, size:247380
filter:1, level:3, strategy:1, size:247380
filter:3, level:1, strategy:0, size:247619
filter:3, level:1, strategy:1, size:247619
filter:3, level:2, strategy:0, size:247704
filter:3, level:2, strategy:1, size:247704
filter:3, level:3, strategy:0, size:247725
filter:3, level:3, strategy:1, size:247725
filter:1, level:1, strategy:0, size:247811
filter:1, level:1, strategy:1, size:247811
filter:2, level:9, strategy:4, size:257312
filter:2, level:8, strategy:4, size:257451
filter:4, level:8, strategy:4, size:257506
filter:4, level:9, strategy:4, size:257519
filter:4, level:4, strategy:4, size:257536
filter:4, level:5, strategy:4, size:257539
filter:4, level:6, strategy:4, size:257546
filter:4, level:7, strategy:4, size:257546
filter:0, level:8, strategy:4, size:257721
filter:0, level:9, strategy:4, size:257721
filter:2, level:4, strategy:4, size:257737
filter:2, level:5, strategy:4, size:257759
filter:2, level:6, strategy:4, size:257759
filter:2, level:7, strategy:4, size:257759
filter:5, level:8, strategy:4, size:258068
filter:5, level:9, strategy:4, size:258075
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filter:0, level:5, strategy:4, size:258105
filter:0, level:6, strategy:4, size:258105
filter:0, level:7, strategy:4, size:258105
filter:5, level:4, strategy:4, size:258190
filter:5, level:5, strategy:4, size:258203
filter:5, level:6, strategy:4, size:258230
filter:5, level:7, strategy:4, size:258230
filter:3, level:8, strategy:4, size:258614
filter:1, level:8, strategy:4, size:258625
filter:1, level:9, strategy:4, size:258625
filter:3, level:9, strategy:4, size:258626
filter:3, level:5, strategy:4, size:258783
filter:3, level:6, strategy:4, size:258783
filter:3, level:7, strategy:4, size:258783
filter:3, level:4, strategy:4, size:258784
filter:1, level:4, strategy:4, size:258847
filter:1, level:5, strategy:4, size:258872
filter:1, level:6, strategy:4, size:258922
filter:1, level:7, strategy:4, size:258922
filter:2, level:1, strategy:4, size:258953
filter:2, level:2, strategy:4, size:258953
filter:2, level:3, strategy:4, size:258953
filter:4, level:2, strategy:4, size:259066
filter:4, level:3, strategy:4, size:259070
filter:4, level:1, strategy:4, size:259143
filter:0, level:1, strategy:4, size:259394
filter:0, level:2, strategy:4, size:259394
filter:0, level:3, strategy:4, size:259394
filter:5, level:3, strategy:4, size:259786
filter:5, level:2, strategy:4, size:259810
filter:5, level:1, strategy:4, size:259811
filter:3, level:1, strategy:4, size:260389
filter:3, level:2, strategy:4, size:260449
filter:3, level:3, strategy:4, size:260473
filter:1, level:2, strategy:4, size:260490
filter:1, level:3, strategy:4, size:260490
filter:1, level:1, strategy:4, size:260568
filter:4, level:0, strategy:3, size:284075
filter:5, level:0, strategy:3, size:284320
filter:1, level:0, strategy:3, size:286960
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filter:4, level:2, strategy:2, size:331440
filter:4, level:3, strategy:2, size:331440
filter:4, level:4, strategy:2, size:331440
filter:4, level:5, strategy:2, size:331440
filter:4, level:6, strategy:2, size:331440
filter:4, level:7, strategy:2, size:331440
filter:4, level:8, strategy:2, size:331440
filter:4, level:9, strategy:2, size:331440
filter:5, level:1, strategy:2, size:331550
filter:5, level:2, strategy:2, size:331550
filter:5, level:3, strategy:2, size:331550
filter:5, level:4, strategy:2, size:331550
filter:5, level:5, strategy:2, size:331550
filter:5, level:6, strategy:2, size:331550
filter:5, level:7, strategy:2, size:331550
filter:5, level:8, strategy:2, size:331550
filter:5, level:9, strategy:2, size:331550
filter:1, level:1, strategy:2, size:331823
filter:1, level:2, strategy:2, size:331823
filter:1, level:3, strategy:2, size:331823
filter:1, level:4, strategy:2, size:331823
filter:1, level:5, strategy:2, size:331823
filter:1, level:6, strategy:2, size:331823
filter:1, level:7, strategy:2, size:331823
filter:1, level:8, strategy:2, size:331823
filter:1, level:9, strategy:2, size:331823
filter:3, level:1, strategy:3, size:346952
filter:3, level:2, strategy:3, size:346952
filter:3, level:3, strategy:3, size:346952
filter:3, level:4, strategy:3, size:346952
filter:3, level:5, strategy:3, size:346952
filter:3, level:6, strategy:3, size:346952
filter:3, level:7, strategy:3, size:346952
filter:3, level:8, strategy:3, size:346952
filter:3, level:9, strategy:3, size:346952
filter:2, level:1, strategy:3, size:358276
filter:2, level:2, strategy:3, size:358276
filter:2, level:3, strategy:3, size:358276
filter:2, level:4, strategy:3, size:358276
filter:2, level:5, strategy:3, size:358276
filter:2, level:6, strategy:3, size:358276
filter:2, level:7, strategy:3, size:358276
filter:2, level:8, strategy:3, size:358276
filter:2, level:9, strategy:3, size:358276
filter:3, level:1, strategy:2, size:429431
filter:3, level:2, strategy:2, size:429431
filter:3, level:3, strategy:2, size:429431
filter:3, level:4, strategy:2, size:429431
filter:3, level:5, strategy:2, size:429431
filter:3, level:6, strategy:2, size:429431
filter:3, level:7, strategy:2, size:429431
filter:3, level:8, strategy:2, size:429431
...

Answer 2

在压缩PNG时我不会仅依赖ImageMagick(除非你自己控制之外的某些原因迫使你去ImageMagick).

比较ImageMagick的结果pngcrush,或者是它的新的继承者,是一个很好的替代方案optipng.

与ImageMagick相比,这两者在优化和压缩方面通常都能获得更好的效果.通常,它们也比IM慢,因为它们可以强制使用不同的方法,然后仅保留最小的结果.

话虽如此,现在使用ImageMagick ......

定义PNG质量的标准方法convert是使用-quality {level}{filter}参数.

-define png:...但是,通过使用控件组合,您可以正确使用更细粒度的控件.

-quality对于PNG很不像JPEG质量设置(这仅仅是一个整数0到100).

对于PNG它是由 -由两个单数字组成:

• 第一个数字({水平})是(主要)zlib压缩级,并且它可以从去0到9.
  (但是,设置0具有特殊含义:当你使用它时,你将得到霍夫曼压缩,而不是zlib压缩等级0.这通常更好......很奇怪但是真的.)

• 第二个数字({filter})是PNG数据编码过滤器类型(在压缩之前):

  • 0表示没有,
  • 1表示"sub",
  • 2表示"向上",
  • 3表示"平均",
  • 4表示"Paeth",和
  • 5表示"自适应".

实际上导致:

• 对于具有固体颜色序列的插图,使用"无"滤波器(-quality 00)的霍夫曼压缩通常是最合适的.
• 对于自然景观的照片,"自适应"过滤(-quality 05)通常是最好的.

要将其转换为命令行语法,请尝试以下设置:

 -define png:compression-level=0  \
 -define png:compression-filter=5 \ 
 -define png:compression-strategy=2 

最后,如果我想真正比较压缩后图像的不同(但接近)清晰度级别,我经常使用Fred Weinstein的精彩flicker_cmp脚本.

让你的妻子测试它...... :-)

PS:这是关于PNG压缩技术的一个很好的指南.

Answer 3

我得到的最佳压缩如下：

convert wallpsw.png -resize 1024x768 -quality 95 \
                    -depth 8 wallpsw-q95-r1024x768-d8.png

结果：

identify wallpsw*

 wallpsw.png PNG 1920x1080 1920x1080+0+0 16-bit DirectClass 4.63MB 0.000u 0:00.000
 wallpsw-q95-r1024x768-d8.png[1] PNG 1024x576 1024x576+0+0 8-bit DirectClass 854KB 0.000u 0:00.000

如果有人知道更好的方法，请告诉我。我找不到。

Answer 4

deflate压缩算法使用65K历史窗口.PNG压缩往往相当慢,因为该过程必须将压缩流中的字节序列与窗口中的字节序列进行比较.

您可以通过限制窗口的搜索来控制压缩的速度.您可能只搜索缓冲区的一半以进行匹配以加快进程(因为压缩率较低).

在JPEG中,权衡是在质量和大小之间.在PNG压缩中,权衡在速度和大小之间.

无论如何,PNG压缩过程总是无损的.

Answer 5

我花了半天时间玩。我确实将图片调整为360x240px。我得到了最好的结果：

 convert -depth 24 -define png:compression-filter=2 \
         -define png:compression-level=9 -define png:compression-strategy=1