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问ImageMagick: PNG的无损最大压缩？
EN

Stack Overflow用户

提问于 2014-12-03 08:41:30

回答 5查看 66.2K关注 0票数 50

当使用ImageMagick保存到无损PNG时，我希望达到最大的压缩量。我正在对许多PSD进行批量转换。

我尝试了一些东西，但在我看来，得到的PNG图像并不像原来的图像那么清晰，虽然我的妻子看不到它。

这些是我正在使用的当前论点：

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：

压缩滤波器为1(子)
最大压缩级别9
压缩策略是2 huffman_only (所以没有过滤，虽然这种压缩过滤器应该是无损的)

根据文档：“有效值为0到4，意味着默认、过滤、huffman_only、rle和固定的zlib压缩策略。如果您使用的是不支持Z_RLE (1.2.0之前)或Z_FIXED (1.2.2.2之前)的旧ZLIB，则值3和4将分别使用zlib默认策略。”

顺便说一下，我的图像是960x720像素。

(如果使用默认压缩策略0，则会得到大文件。可能是9的压缩过滤器和0的压缩策略正在产生更小的图像，但我仍然不确定它是否是无损的)。

问题：

这是无损压缩吗？如果没有，哪里有错误？
知道如何实现更好的无损压缩吗？

imagemagick

png

imagemagick-convert

libpng

回答 5

Stack Overflow用户

发布于 2014-12-03 10:29:10

我认为您已经达到或超过了ImageMagick文档的极限，我想建议您根据经验计算出您的答案--或者如果您确实得到了一个明确的答案，那么您至少要对其进行经验测试。

我无法访问您的图像，因此我自己生成了一个参考图像，如下所示。它包含一个易于压缩的固体颜色块(红色)，一个黑白梯度和一堆噪音，所以有一些东西可以使大多数类型的压缩快乐或不愉快。

为了测试您是否具有无损压缩，我建议您将图像转换为PPM格式-参见这里。这不包含日期，时间或统计数据或任何东西，但纯图像数据和大小的一种非常简单的格式-从而允许比较像素值是否已改变通过压缩。

然后，我编写了如下脚本，使用所有可能的过滤器、策略和级别来压缩参考图像，以查看文件大小，如果它们遭受了任何损失，因此与参考PPM图像不同：

下面是脚本：

#!/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，所以我使用的任何参数似乎都没有压缩损失。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，您的数字将是不同的，因为您的图像是不同的，所以您将不得不看看什么对您的数据-但希望这将是一个起点。

请注意，如果我按大小对上面的内容进行排序，就会得到以下结果：

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
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...

票数 72

Stack Overflow用户

发布于 2014-12-03 10:40:01

在压缩PNG时，我不会只依赖ImageMagick (除非有某种原因超出了您自己的控制范围，迫使您使用ImageMagick)。

要将ImageMagick的结果与之进行比较，一个很好的选择是压碎，或者它的较新的继承者optipng。

与ImageMagick相比，这两种方法在优化和压缩方面都取得了更好的效果。通常，他们也比IM慢，因为他们可以蛮力不同的方法，然后保持最小的结果。

话虽如此，现在ImageMagick.

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

不过，您使用通过使用-define png:...控件组合获得的更细粒度的控件是正确的。

用于PNG的-quality与JPEG的质量设置非常不同(后者只是从0到100的整数)。

对于PNG来说，它是由两个个位数组成的：

第一个数字({level})是(很大程度上) zlib压缩级别，它可以从0到9。 (然而，0的设置有一个特殊的含义:当您使用它时，您将得到Huffman压缩，而不是zlib压缩级别0。这往往更好..。奇怪但却是真的。
第二个数字({ filter })是PNG数据编码过滤器类型(在压缩之前)：

- 0 means none, 
- 1 means "sub", 
- 2 means "up", 
- 3 means "average", 
- 4 means "Paeth", and 
- 5 means "adaptive".

在实际中的结果是：

对于彩色实心序列的插图，霍夫曼用“无”滤波器(-quality 00)压缩通常是最合适的。
对于自然景观的照片，“自适应”滤波(-quality 05)通常是最好的。

若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，如果我真的想比较压缩后图像的不同(但接近)清晰度，我经常使用frequently的出色的flicker_cmp脚本。

让你妻子来测试..。:-)

P.S.：这里是关于PNG压缩技术的一个很好的指南。

票数 47

Stack Overflow用户

发布于 2014-12-03 18:54:47

压缩算法使用65K历史窗口。PNG压缩往往相当慢，因为进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。

通过限制对窗口的搜索，可以控制压缩的速度。您可能只搜索一半的缓冲区匹配，以加快进程(作为较低的压缩风险)。

在JPEG中，权衡的是质量和大小。在PNG压缩中，需要在速度和大小之间进行权衡。

无论如何，PNG压缩过程始终是无损的。

票数 8

页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持

原文链接：

https://stackoverflow.com/questions/27267073

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