改进 PNG 优化 Gulp 任务

Question

这是具有透明度的源 PNG：http://i.imgur.com/7m0zIBp.png (13.3kB)

• 使用compresspng.com优化：http://i.imgur.com/DHUiLuO.png (5.4kB)
• 使用 tinypng.com 优化：http://i.imgur.com/rEE2hzg.png (5.6kB)
• 使用 gulp-imagemin+imagemin-pngquant 优化：http://i.imgur.com/OTqI6lK.png (6.6kB)

正如您所见，在线工具比 Gulp 更好。有没有办法使用 Gulp 改进 PNG 优化？

以防万一，这是我的 gulp 任务：

gulp.task('images', function() {
  return gulp.src('frontend/images/*')
    .pipe(imagemin({
      progressive: true,
      use: [pngquant()]
    }))
    .pipe(gulp.dest('public/images'));
});

Answer 1

您可以使用 ImageMagick 的identify -verbose 工具查看各种算法的作用，如下所示

identify -verbose com.png    > com.txt
identify -verbose tin.png    > tin.txt
identify -verbose gulp.png   > gulp.txt

然后比较输出 - 我在 Mac 上使用 opendiff。如果将 com.txt (compresspng) 与 gulp.txt 进行比较，您会看到这一点

如果你比较 tiny (tinypng) 和 gulp.txt

区别在于保留的颜色数量 - gulp 使用 94 种颜色，compresspng 使用 66 种，tiny 使用 53 种。

如果您或其他任何人希望比较任何其他方面，我将粘贴在下面的 3 个输出文件中以供参考：

gulp.txt

Image: gulp.png
  Format: PNG (Portable Network Graphics)
  Mime type: image/png
  Class: DirectClass
  Geometry: 560x290+0+0
  Units: Undefined
  Type: PaletteAlpha
  Endianess: Undefined
  Colorspace: sRGB
  Depth: 8-bit
  Channel depth:
    red: 8-bit
    green: 8-bit
    blue: 8-bit
    alpha: 8-bit
  Channel statistics:
    Pixels: 162400
    Red:
      min: 1 (0.00392157)
      max: 245 (0.960784)
      mean: 110.922 (0.434989)
      standard deviation: 104.067 (0.408106)
      kurtosis: -1.74946
      skewness: 0.208663
      entropy: 0.3477
    Green:
      min: 40 (0.156863)
      max: 245 (0.960784)
      mean: 124.973 (0.490091)
      standard deviation: 61.139 (0.239761)
      kurtosis: -1.32326
      skewness: 0.222376
      entropy: 0.330503
    Blue:
      min: 113 (0.443137)
      max: 244 (0.956863)
      mean: 170.131 (0.667179)
      standard deviation: 53.7786 (0.210897)
      kurtosis: -1.86628
      skewness: 0.233095
      entropy: 0.346704
    Alpha:
      min: 0 (0)
      max: 255 (1)
      mean: 197.075 (0.772845)
      standard deviation: 106.443 (0.417423)
      kurtosis: -0.298155
      skewness: 1.3014
      entropy: 0.157855
  Image statistics:
    Overall:
      min: 0 (0)
      max: 255 (1)
      mean: 115.988 (0.454854)
      standard deviation: 84.8383 (0.332699)
      kurtosis: -0.730342
      skewness: 0.117783
      entropy: 0.295691
  Alpha: srgba(76,105,113,0)   #4C697100
  Colors: 94
  Histogram:
       660: (  1, 40,117,255) #012875 srgba(1,40,117,1)
         8: (  1, 58,131,255) #013A83 srgba(1,58,131,1)
         4: (  1, 66,138,255) #01428A srgba(1,66,138,1)
         6: (  1, 75,145,255) #014B91 srgba(1,75,145,1)
         2: (  1, 84,152,255) #015498 srgba(1,84,152,1)
         4: (  1, 93,159,255) #015D9F srgba(1,93,159,1)
         3: (  1,102,166,255) #0166A6 srgba(1,102,166,1)
         6: (  1,111,173,255) #016FAD srgba(1,111,173,1)
         4: (  1,119,180,255) #0177B4 srgba(1,119,180,1)
         4: (  1,128,187,255) #0180BB srgba(1,128,187,1)
         1: (  1,137,194,255) #0189C2 srgba(1,137,194,1)
        20: (  1,146,201,255) #0192C9 srgba(1,146,201,1)
         5: (  1,155,208,255) #019BD0 srgba(1,155,208,1)
         3: (  1,163,215,255) #01A3D7 srgba(1,163,215,1)
         5: (  1,172,222,255) #01ACDE srgba(1,172,222,1)
     59271: (  1,181,229,255) #01B5E5 srgba(1,181,229,1)
        91: (  1,181,229,143) #01B5E58F srgba(1,181,229,0.560784)
        80: (  1,181,229,224) #01B5E5E0 srgba(1,181,229,0.878431)
        79: (  1,181,229,  1) #01B5E501 srgba(1,181,229,0.00392157)
        66: (  1,181,229, 64) #01B5E540 srgba(1,181,229,0.25098)
        61: (  1,181,229, 16) #01B5E510 srgba(1,181,229,0.0627451)
        54: (  1,181,229, 36) #01B5E524 srgba(1,181,229,0.141176)
        50: (  1,181,229, 99) #01B5E563 srgba(1,181,229,0.388235)
        46: (  1,181,229,168) #01B5E5A8 srgba(1,181,229,0.658824)
        46: (  1,181,229,  9) #01B5E509 srgba(1,181,229,0.0352941)
        45: (  1,181,229,  4) #01B5E504 srgba(1,181,229,0.0156863)
        39: (  1,181,229,195) #01B5E5C3 srgba(1,181,229,0.764706)
        32: (  1,181,229, 25) #01B5E519 srgba(1,181,229,0.0980392)
        30: (  1,181,229,120) #01B5E578 srgba(1,181,229,0.470588)
        29: (  1,181,229, 80) #01B5E550 srgba(1,181,229,0.313725)
        29: (  1,181,229, 49) #01B5E531 srgba(1,181,229,0.192157)
         4: ( 15, 41,118,255) #0F2976 srgba(15,41,118,1)
        64: ( 16,185,230,255) #10B9E6 srgba(16,185,230,1)
         4: ( 30, 42,119,255) #1E2A77 srgba(30,42,119,1)
        40: ( 32,189,231,255) #20BDE7 srgba(32,189,231,1)
         3: ( 44, 43,119,255) #2C2B77 srgba(44,43,119,1)
        46: ( 47,193,232,255) #2FC1E8 srgba(47,193,232,1)
         7: ( 59, 44,120,255) #3B2C78 srgba(59,44,120,1)
       281: ( 62,197,233,255) #3EC5E9 srgba(62,197,233,1)
         3: ( 73, 45,121,255) #492D79 srgba(73,45,121,1)
     35876: ( 76,105,113,  0) #4C697100 srgba(76,105,113,0)
        29: ( 77,201,234,255) #4DC9EA srgba(77,201,234,1)
         1: ( 88, 46,122,255) #582E7A srgba(88,46,122,1)
        39: ( 93,205,235,255) #5DCDEB srgba(93,205,235,1)
         5: (102, 47,123,255) #662F7B srgba(102,47,123,1)
        24: (108,209,236,255) #6CD1EC srgba(108,209,236,1)
        18: (117, 48,124,255) #75307C srgba(117,48,124,1)
       267: (123,213,237,255) #7BD5ED srgba(123,213,237,1)
         3: (131, 49,124,255) #83317C srgba(131,49,124,1)
        27: (138,217,237,255) #8AD9ED srgba(138,217,237,1)
         2: (145, 50,125,255) #91327D srgba(145,50,125,1)
        28: (154,221,238,255) #9ADDEE srgba(154,221,238,1)
         4: (160, 51,126,255) #A0337E srgba(160,51,126,1)
        16: (169,225,239,255) #A9E1EF srgba(169,225,239,1)
        16: (174, 52,127,255) #AE347F srgba(174,52,127,1)
       202: (184,229,240,255) #B8E5F0 srgba(184,229,240,1)
        41: (199,233,241,255) #C7E9F1 srgba(199,233,241,1)
         2: (203, 54,128,255) #CB3680 srgba(203,54,128,1)
        43: (215,237,242,255) #D7EDF2 srgba(215,237,242,1)
         2: (216, 55,129,195) #D83781C3 srgba(216,55,129,0.764706)
         3: (218, 55,129,255) #DA3781 srgba(218,55,129,1)
        49: (230,241,243,255) #E6F1F3 srgba(230,241,243,1)
     53788: (232, 56,130,255) #E83882 srgba(232,56,130,1)
        77: (232, 56,130, 99) #E8388263 srgba(232,56,130,0.388235)
        72: (232, 56,130, 16) #E8388210 srgba(232,56,130,0.0627451)
        71: (232, 56,130,143) #E838828F srgba(232,56,130,0.560784)
        69: (232, 56,130,224) #E83882E0 srgba(232,56,130,0.878431)
        65: (232, 56,130, 64) #E8388240 srgba(232,56,130,0.25098)
        62: (232, 56,130,195) #E83882C3 srgba(232,56,130,0.764706)
        52: (232, 56,130, 36) #E8388224 srgba(232,56,130,0.141176)
        52: (232, 56,130,  4) #E8388204 srgba(232,56,130,0.0156863)
        52: (232, 56,130,  1) #E8388201 srgba(232,56,130,0.00392157)
        46: (232, 56,130,  9) #E8388209 srgba(232,56,130,0.0352941)
        34: (232, 56,130, 80) #E8388250 srgba(232,56,130,0.313725)
        33: (232, 56,130,168) #E83882A8 srgba(232,56,130,0.658824)
        27: (232, 56,130, 25) #E8388219 srgba(232,56,130,0.0980392)
        26: (232, 56,130,120) #E8388278 srgba(232,56,130,0.470588)
        22: (232, 56,130, 49) #E8388231 srgba(232,56,130,0.192157)
        57: (233, 68,137,255) #E94489 srgba(233,68,137,1)
        34: (234, 80,144,255) #EA5090 srgba(234,80,144,1)
        62: (234, 91,151,255) #EA5B97 srgba(234,91,151,1)
       402: (235,103,159,255) #EB679F srgba(235,103,159,1)
        51: (236,115,166,255) #EC73A6 srgba(236,115,166,1)
        35: (237,127,173,255) #ED7FAD srgba(237,127,173,1)
        34: (238,139,180,255) #EE8BB4 srgba(238,139,180,1)
        43: (239,151,187,255) #EF97BB srgba(239,151,187,1)
        44: (239,162,194,255) #EFA2C2 srgba(239,162,194,1)
        56: (240,174,201,255) #F0AEC9 srgba(240,174,201,1)
        38: (241,186,208,255) #F1BAD0 srgba(241,186,208,1)
        58: (242,198,216,255) #F2C6D8 srgba(242,198,216,1)
        41: (243,210,223,255) #F3D2DF srgba(243,210,223,1)
        53: (243,221,230,255) #F3DDE6 srgba(243,221,230,1)
        71: (244,233,237,255) #F4E9ED srgba(244,233,237,1)
      8841: (245,245,244,255) #F5F5F4 srgba(245,245,244,1)
  Rendering intent: Perceptual
  Gamma: 0.45455
  Chromaticity:
    red primary: (0.64,0.33)
    green primary: (0.3,0.6)
    blue primary: (0.15,0.06)
    white point: (0.3127,0.329)
  Background color: white
  Border color: srgba(223,223,223,1)
  Matte color: grey74
  Transparent color: none
  Interlace: None
  Intensity: Undefined
  Compose: Over
  Page geometry: 560x290+0+0
  Dispose: Undefined
  Iterations: 0
  Compression: Zip
  Orientation: Undefined
  Properties:
    date:create: 2015-03-19T10:05:06+00:00
    date:modify: 2015-03-19T10:05:06+00:00
    png:cHRM: chunk was found (see Chromaticity, above)
    png:gAMA: gamma=0.45455 (See Gamma, above)
    png:IHDR.bit-depth-orig: 8
    png:IHDR.bit_depth: 8
    png:IHDR.color-type-orig: 3
    png:IHDR.color_type: 3 (Indexed)
    png:IHDR.interlace_method: 0 (Not interlaced)
    png:IHDR.width,height: 560, 290
    png:PLTE.number_colors: 94
    png:sRGB: intent=0 (Perceptual Intent)
    png:tRNS: chunk was found
    signature: 91476421108f784ce82d392aa2e58bc6c8c5991cf6466f5db98809cc16f0f2ca
  Artifacts:
    filename: gulp.png
    verbose: true
  Tainted: False
  Filesize: 6.63KB
  Number pixels: 162K
  Pixels per second: 0B
  User time: 0.000u
  Elapsed time: 0:01.000
  Version: ImageMagick 6.9.0-10 Q16 x86_64 2015-03-10 http://www.imagemagick.org

tin.txt

Image: tin.png
  Format: PNG (Portable Network Graphics)
  Mime type: image/png
  Class: DirectClass
  Geometry: 560x290+0+0
  Units: Undefined
  Type: PaletteAlpha
  Endianess: Undefined
  Colorspace: sRGB
  Depth: 8-bit
  Channel depth:
    red: 8-bit
    green: 8-bit
    blue: 8-bit
    alpha: 8-bit
  Channel statistics:
    Pixels: 162400
    Red:
      min: 0 (0)
      max: 245 (0.960784)
      mean: 94.0738 (0.368917)
      standard deviation: 113.927 (0.446772)
      kurtosis: -1.82471
      skewness: 0.407541
      entropy: 0.400756
    Green:
      min: 0 (0)
      max: 245 (0.960784)
      mean: 101.679 (0.398739)
      standard deviation: 81.0101 (0.317687)
      kurtosis: -1.50733
      skewness: 0.171586
      entropy: 0.386438
    Blue:
      min: 0 (0)
      max: 244 (0.956863)
      mean: 145.019 (0.568702)
      standard deviation: 89.1803 (0.349727)
      kurtosis: -1.06731
      skewness: -0.563292
      entropy: 0.389441
    Alpha:
      min: 0 (0)
      max: 255 (1)
      mean: 197.073 (0.772837)
      standard deviation: 106.446 (0.417434)
      kurtosis: -0.298278
      skewness: 1.30136
      entropy: 0.179828
  Image statistics:
    Overall:
      min: 0 (0)
      max: 255 (1)
      mean: 99.6745 (0.39088)
      standard deviation: 98.5213 (0.386358)
      kurtosis: -1.37999
      skewness: 0.35773
      entropy: 0.339116
  Alpha: none   #00000000
  Colors: 53
  Histogram:
     36007: (  0,  0,  0,  0) #00000000 none
       664: (  1, 40,117,255) #012875 srgba(1,40,117,1)
        12: (  1, 60,133,255) #013C85 srgba(1,60,133,1)
        12: (  1, 82,151,255) #015297 srgba(1,82,151,1)
        17: (  1,115,177,255) #0173B1 srgba(1,115,177,1)
        29: (  1,149,204,255) #0195CC srgba(1,149,204,1)
     59276: (  1,181,229,255) #01B5E5 srgba(1,181,229,1)
        95: (  1,181,229, 69) #01B5E545 srgba(1,181,229,0.270588)
        93: (  1,181,229, 19) #01B5E513 srgba(1,181,229,0.0745098)
        91: (  1,181,229,143) #01B5E58F srgba(1,181,229,0.560784)
        83: (  1,181,229, 40) #01B5E528 srgba(1,181,229,0.156863)
        80: (  1,181,229,224) #01B5E5E0 srgba(1,181,229,0.878431)
        50: (  1,181,229, 99) #01B5E563 srgba(1,181,229,0.388235)
        46: (  1,181,229,168) #01B5E5A8 srgba(1,181,229,0.658824)
        39: (  1,181,229,195) #01B5E5C3 srgba(1,181,229,0.764706)
        30: (  1,181,229,120) #01B5E578 srgba(1,181,229,0.470588)
        64: ( 16,185,230,255) #10B9E6 srgba(16,185,230,1)
         7: ( 36, 42,119,255) #242A77 srgba(36,42,119,1)
        86: ( 40,191,232,255) #28BFE8 srgba(40,191,232,1)
       281: ( 62,197,233,255) #3EC5E9 srgba(62,197,233,1)
        11: ( 65, 44,120,255) #412C78 srgba(65,44,120,1)
        68: ( 86,204,235,255) #56CCEB srgba(86,204,235,1)
        24: (108,209,236,255) #6CD1EC srgba(108,209,236,1)
        28: (118, 48,124,255) #76307C srgba(118,48,124,1)
       267: (123,213,237,255) #7BD5ED srgba(123,213,237,1)
       189: (133,121,180,  6) #8579B406 srgba(133,121,180,0.0235294)
        55: (146,219,238,255) #92DBEE srgba(146,219,238,1)
        22: (174, 52,127,255) #AE347F srgba(174,52,127,1)
       218: (183,229,240,255) #B7E5F0 srgba(183,229,240,1)
        84: (208,235,242,255) #D0EBF2 srgba(208,235,242,1)
        49: (230,241,243,255) #E6F1F3 srgba(230,241,243,1)
     53791: (232, 56,130,255) #E83882 srgba(232,56,130,1)
       103: (232, 56,130,104) #E8388268 srgba(232,56,130,0.407843)
        99: (232, 56,130, 18) #E8388212 srgba(232,56,130,0.0705882)
        87: (232, 56,130, 60) #E838823C srgba(232,56,130,0.235294)
        71: (232, 56,130,143) #E838828F srgba(232,56,130,0.560784)
        69: (232, 56,130,224) #E83882E0 srgba(232,56,130,0.878431)
        64: (232, 56,130,195) #E83882C3 srgba(232,56,130,0.764706)
        52: (232, 56,130, 36) #E8388224 srgba(232,56,130,0.141176)
        34: (232, 56,130, 80) #E8388250 srgba(232,56,130,0.313725)
        33: (232, 56,130,168) #E83882A8 srgba(232,56,130,0.658824)
        91: (234, 72,140,255) #EA488C srgba(234,72,140,1)
        62: (234, 91,151,255) #EA5B97 srgba(234,91,151,1)
       402: (235,103,159,255) #EB679F srgba(235,103,159,1)
        51: (236,115,166,255) #EC73A6 srgba(236,115,166,1)
        35: (237,127,173,255) #ED7FAD srgba(237,127,173,1)
        77: (239,146,184,255) #EF92B8 srgba(239,146,184,1)
        44: (239,162,194,255) #EFA2C2 srgba(239,162,194,1)
        56: (240,174,201,255) #F0AEC9 srgba(240,174,201,1)
        96: (242,194,213,255) #F2C2D5 srgba(242,194,213,1)
        94: (243,217,227,255) #F3D9E3 srgba(243,217,227,1)
        71: (244,233,237,255) #F4E9ED srgba(244,233,237,1)
      8841: (245,245,244,255) #F5F5F4 srgba(245,245,244,1)
  Rendering intent: Perceptual
  Gamma: 0.454545
  Chromaticity:
    red primary: (0.64,0.33)
    green primary: (0.3,0.6)
    blue primary: (0.15,0.06)
    white point: (0.3127,0.329)
  Background color: white
  Border color: srgba(223,223,223,1)
  Matte color: grey74
  Transparent color: none
  Interlace: None
  Intensity: Undefined
  Compose: Over
  Page geometry: 560x290+0+0
  Dispose: Undefined
  Iterations: 0
  Compression: Zip
  Orientation: Undefined
  Properties:
    date:create: 2015-03-19T10:04:55+00:00
    date:modify: 2015-03-19T10:04:55+00:00
    png:IHDR.bit-depth-orig: 8
    png:IHDR.bit_depth: 8
    png:IHDR.color-type-orig: 3
    png:IHDR.color_type: 3 (Indexed)
    png:IHDR.interlace_method: 0 (Not interlaced)
    png:IHDR.width,height: 560, 290
    png:PLTE.number_colors: 53
    png:sRGB: intent=0 (Perceptual Intent)
    png:tRNS: chunk was found
    signature: f7e69fb1d6be1bde229a91d820f0f42330b923a37e28f0fccb181fdd6485c81c
  Artifacts:
    filename: tin.png
    verbose: true
  Tainted: False
  Filesize: 5.59KB
  Number pixels: 162K
  Pixels per second: 0B
  User time: 0.000u
  Elapsed time: 0:01.000
  Version: ImageMagick 6.9.0-10 Q16 x86_64 2015-03-10 http://www.imagemagick.org

com.txt

Image: com.png
  Format: PNG (Portable Network Graphics)
  Mime type: image/png
  Class: DirectClass
  Geometry: 560x290+0+0
  Units: Undefined
  Type: PaletteAlpha
  Endianess: Undefined
  Colorspace: sRGB
  Depth: 8-bit
  Channel depth:
    red: 8-bit
    green: 8-bit
    blue: 8-bit
    alpha: 8-bit
  Channel statistics:
    Pixels: 162400
    Red:
      min: 1 (0.00392157)
      max: 245 (0.960784)
      mean: 110.909 (0.434937)
      standard deviation: 104.021 (0.407927)
      kurtosis: -1.74831
      skewness: 0.209362
      entropy: 0.377289
    Green:
      min: 40 (0.156863)
      max: 245 (0.960784)
      mean: 124.952 (0.490008)
      standard deviation: 61.1171 (0.239675)
      kurtosis: -1.32134
      skewness: 0.22372
      entropy: 0.367959
    Blue:
      min: 113 (0.443137)
      max: 244 (0.956863)
      mean: 170.07 (0.66694)
      standard deviation: 53.7829 (0.210913)
      kurtosis: -1.86532
      skewness: 0.235003
      entropy: 0.37823
    Alpha:
      min: 0 (0)
      max: 255 (1)
      mean: 197.074 (0.772839)
      standard deviation: 106.445 (0.417433)
      kurtosis: -0.298201
      skewness: 1.30139
      entropy: 0.169804
  Image statistics:
    Overall:
      min: 0 (0)
      max: 255 (1)
      mean: 115.964 (0.454761)
      standard deviation: 84.8218 (0.332635)
      kurtosis: -0.729488
      skewness: 0.118667
      entropy: 0.32332
  Alpha: srgba(76,105,113,0)   #4C697100
  Colors: 66
  Histogram:
       664: (  1, 40,117,255) #012875 srgba(1,40,117,1)
        12: (  1, 60,133,255) #013C85 srgba(1,60,133,1)
        12: (  1, 82,151,255) #015297 srgba(1,82,151,1)
        17: (  1,115,177,255) #0173B1 srgba(1,115,177,1)
        29: (  1,149,204,255) #0195CC srgba(1,149,204,1)
     59276: (  1,181,229,255) #01B5E5 srgba(1,181,229,1)
        91: (  1,181,229,143) #01B5E58F srgba(1,181,229,0.560784)
        91: (  1,181,229,  6) #01B5E506 srgba(1,181,229,0.0235294)
        86: (  1,181,229, 32) #01B5E520 srgba(1,181,229,0.12549)
        80: (  1,181,229,224) #01B5E5E0 srgba(1,181,229,0.878431)
        66: (  1,181,229, 64) #01B5E540 srgba(1,181,229,0.25098)
        61: (  1,181,229, 16) #01B5E510 srgba(1,181,229,0.0627451)
        50: (  1,181,229, 99) #01B5E563 srgba(1,181,229,0.388235)
        46: (  1,181,229,168) #01B5E5A8 srgba(1,181,229,0.658824)
        39: (  1,181,229,195) #01B5E5C3 srgba(1,181,229,0.764706)
        30: (  1,181,229,120) #01B5E578 srgba(1,181,229,0.470588)
        29: (  1,181,229, 49) #01B5E531 srgba(1,181,229,0.192157)
        29: (  1,181,229, 80) #01B5E550 srgba(1,181,229,0.313725)
        64: ( 16,185,230,255) #10B9E6 srgba(16,185,230,1)
        40: ( 32,189,231,255) #20BDE7 srgba(32,189,231,1)
        46: ( 47,193,232,255) #2FC1E8 srgba(47,193,232,1)
        17: ( 52, 43,120,255) #342B78 srgba(52,43,120,1)
       281: ( 62,197,233,255) #3EC5E9 srgba(62,197,233,1)
     36007: ( 76,105,113,  0) #4C697100 srgba(76,105,113,0)
        29: ( 77,201,234,255) #4DC9EA srgba(77,201,234,1)
        39: ( 93,205,235,255) #5DCDEB srgba(93,205,235,1)
        24: (108,209,236,255) #6CD1EC srgba(108,209,236,1)
        27: (115, 48,124,255) #73307C srgba(115,48,124,1)
       267: (123,213,237,255) #7BD5ED srgba(123,213,237,1)
        27: (138,217,237,255) #8AD9ED srgba(138,217,237,1)
        44: (160,223,239,255) #A0DFEF srgba(160,223,239,1)
        22: (169, 51,127,255) #A9337F srgba(169,51,127,1)
       202: (184,229,240,255) #B8E5F0 srgba(184,229,240,1)
        41: (199,233,241,255) #C7E9F1 srgba(199,233,241,1)
         5: (212, 54,129,255) #D43681 srgba(212,54,129,1)
        43: (215,237,242,255) #D7EDF2 srgba(215,237,242,1)
         2: (216, 55,129,195) #D83781C3 srgba(216,55,129,0.764706)
        49: (230,241,243,255) #E6F1F3 srgba(230,241,243,1)
     53788: (232, 56,130,255) #E83882 srgba(232,56,130,1)
        99: (232, 56,130, 18) #E8388212 srgba(232,56,130,0.0705882)
        98: (232, 56,130,  6) #E8388206 srgba(232,56,130,0.0235294)
        77: (232, 56,130, 99) #E8388263 srgba(232,56,130,0.388235)
        71: (232, 56,130,143) #E838828F srgba(232,56,130,0.560784)
        69: (232, 56,130,224) #E83882E0 srgba(232,56,130,0.878431)
        65: (232, 56,130, 64) #E8388240 srgba(232,56,130,0.25098)
        62: (232, 56,130,195) #E83882C3 srgba(232,56,130,0.764706)
        52: (232, 56,130, 36) #E8388224 srgba(232,56,130,0.141176)
        34: (232, 56,130, 80) #E8388250 srgba(232,56,130,0.313725)
        33: (232, 56,130,168) #E83882A8 srgba(232,56,130,0.658824)
        26: (232, 56,130,120) #E8388278 srgba(232,56,130,0.470588)
        22: (232, 56,130, 49) #E8388231 srgba(232,56,130,0.192157)
        57: (233, 68,137,255) #E94489 srgba(233,68,137,1)
        34: (234, 80,144,255) #EA5090 srgba(234,80,144,1)
        62: (234, 91,151,255) #EA5B97 srgba(234,91,151,1)
       402: (235,103,159,255) #EB679F srgba(235,103,159,1)
        51: (236,115,166,255) #EC73A6 srgba(236,115,166,1)
        69: (238,133,177,255) #EE85B1 srgba(238,133,177,1)
        43: (239,151,187,255) #EF97BB srgba(239,151,187,1)
        44: (239,162,194,255) #EFA2C2 srgba(239,162,194,1)
        56: (240,174,201,255) #F0AEC9 srgba(240,174,201,1)
        38: (241,186,208,255) #F1BAD0 srgba(241,186,208,1)
        58: (242,198,216,255) #F2C6D8 srgba(242,198,216,1)
        41: (243,210,223,255) #F3D2DF srgba(243,210,223,1)
        53: (243,221,230,255) #F3DDE6 srgba(243,221,230,1)
        71: (244,233,237,255) #F4E9ED srgba(244,233,237,1)
      8841: (245,245,244,255) #F5F5F4 srgba(245,245,244,1)
  Rendering intent: Perceptual
  Gamma: 0.454545
  Chromaticity:
    red primary: (0.64,0.33)
    green primary: (0.3,0.6)
    blue primary: (0.15,0.06)
    white point: (0.3127,0.329)
  Background color: white
  Border color: srgba(223,223,223,1)
  Matte color: grey74
  Transparent color: none
  Interlace: None
  Intensity: Undefined
  Compose: Over
  Page geometry: 560x290+0+0
  Dispose: Undefined
  Iterations: 0
  Compression: Zip
  Orientation: Undefined
  Properties:
    date:create: 2015-03-19T10:04:45+00:00
    date:modify: 2015-03-19T10:04:45+00:00
    png:IHDR.bit-depth-orig: 8
    png:IHDR.bit_depth: 8
    png:IHDR.color-type-orig: 3
    png:IHDR.color_type: 3 (Indexed)
    png:IHDR.interlace_method: 0 (Not interlaced)
    png:IHDR.width,height: 560, 290
    png:PLTE.number_colors: 66
    png:sRGB: intent=0 (Perceptual Intent)
    png:tRNS: chunk was found
    signature: 4fe0f71265e48080cff87d20e1ddb116af764c8429df9e1ef2b1460aeaf6b6a6
  Artifacts:
    filename: com.png
    verbose: true
  Tainted: False
  Filesize: 5.41KB
  Number pixels: 162K
  Pixels per second: 0B
  User time: 0.000u
  Elapsed time: 0:01.000
  Version: ImageMagick 6.9.0-10 Q16 x86_64 2015-03-10 http://www.imagemagick.org

Answer 2

我花了很多时间来实现和设计压缩算法，所以让我给出一个部分答案——尽管这可能不是你想听到的。

如果您了解 png 文件格式的压缩是如何工作的，请阅读 f.ex。 here，您会发现它使用 Deflate 压缩和预测器。 Deflate 压缩是一种无损压缩算法——即使你可以用更好或更差的压缩来实现它，我认为大多数实现在压缩级别方面会产生大致相同的结果。现在大多数人不再费心实现 deflate，所以压缩本身可能对你没有任何好处。

您所链接的工具之类的工作方式是将 RGB 颜色映射到索引颜色。如果您只有有限数量的颜色（例如 256 种），您可以将图像转换为索引表示并再次保存。更少的颜色意味着要编码的信息更少，这意味着您的压缩级别正在上升。如果您的图像仅使用几种颜色，或者您愿意放弃信息，则可以选择此选项。

知道要查找什么，我认为您几乎可以在任何图像包中使用相同的技巧，包括 f.ex。 ImageMagick，瘸子。 （在 Gimp f.ex. 中，您可以执行图像 -> 模式 -> 索引并在所有选项关闭的情况下再次保存）。