Optimization optimization PNG Gulp

Question

This is the original PNG with transparency: http://i.imgur.com/7m0zIBp.png (13.3kB)

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

As you can see, online tools are better than gulp. Is there a way to improve PNG optimization with Gulp?

Just in case, here is my gulp task:

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

Answer 1

You can verify that you have done various algorithms using the ImageMagick tool identify -verbose , for example

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

and then compare the outputs - I use opendiff on a Mac. You will see this if you compare com.txt (compresspng) and gulp.txt

and if you compare tinypng against gulp.txt

The difference in the number of colors saved is that gulp uses 94 colors, compresspng uses 66, and tiny uses 53.

If you or anyone else wants to compare any other aspects, I insert the 3 outoput files below for reference:

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

I spent a lot of time implementing and developing compression algorithms, so let me give a partial answer - although this is probably not what you want to hear.

If you read about how png file compression works, f.ex. here , you will find out that it uses Deflate compression along with a predictor. Deflate compression is a lossless compression algorithm - and even if you can implement it with better or worse compression, I would assume that most implementations will produce about the same result in terms of compression level. Nowadays, most people are no longer bothered by the introduction of deflate, so squeezing it yourself probably won't do you any good.

A method similar to the one you are associated with is matching RGB colors with indexed colors. If you have only a limited number of colors (say 256), you can convert your image to an indexed view and save it again. Fewer colors mean less coding information, which means that the compression level is increasing. If your image uses only a few colors or if you want to lose information, this may be an option.

Knowing what to look for, I think you can do the same trick in almost any image package that includes, for example, f.ex. ImageMagick, Gimp. (In Gimp f.ex. you can make the image mode → -> indexed and save again with all the parameters).