How to threshold an image to get about same amount of black and white?

[konstantin]

Yes, in fact I need a cumulative histogram, but I had no clue that ImageMagick can provide it.

[fmw42]

Yes, in fact I need a cumulative histogram, but I had no clue that ImageMagick can provide it.

It does not have the ability to output a cumulative histogram directly. You can script that. But both -contrast-stretch and -linear-stretch use it when expressing arguments in percent.

[snibgo]

Cumulative histograms, and related processes, are available with my process modules:

Code: Select all

f:\web\im>"%IMDEV%convert" 7cXqWHe.jpg -colorspace gray -process 'mkhisto cumulnorm' -process invclut -crop 2x1@ -delete 0 +repage -crop 1x1+0+0 +repage txt:

# ImageMagick pixel enumeration: 1,1,255,gray
0,0: (79,79,79)  #4F4F4F  gray(79)

[fmw42]

I have a script to do that also for Unix systems. See http://www.fmwconcepts.com/imagemagick/ ... /index.php, though it is 8 bit (256 bins) limited, now.

[konstantin]

JB in facebook colours:

[konstantin]

Maybe such a bisection / binary search method should be implemented in ImageMagick (similarly to Excel solver) to help maximize certain image properties. For example to find a gamma value against maximizing the black-white pixel transitions (edges) on the thresholded image, or simply find the thresholding graylevel value for maximizing a term defined by the ImageMagick built-in fx-language: http://www.imagemagick.org/script/fx.php

[snibgo]

It's a technique that I use frequently, for example "Find the gamma that maximises standard deviation", or "Find the sigmoidal-contrast setting that results in a desired standard deviation".

Including a generic solver in IM would be useful, and faster than doing it in a script (because it wouldn't need to write and re-read). The software engineering would be non-trivial. But don't let that put you off if you have a spare month or three.

[konstantin]

I cant' help, I can't code in C. Only Ruby, as I am a self-taught hobby programmer.

[konstantin]

Sometimes the histogram data is provided in a different way, which doesn't show the usual graylevels, I have no clue why:

Code: Select all

Histogram:
         1: ( 19, 19, 19) #131313 srgb(19,19,19)
         2: ( 20, 20, 20) #141414 grey8
         4: ( 22, 22, 22) #161616 srgb(22,22,22)
         4: ( 23, 23, 23) #171717 grey9
         8: ( 24, 24, 24) #181818 srgb(24,24,24)
         5: ( 25, 25, 25) #191919 srgb(25,25,25)
         9: ( 26, 26, 26) #1A1A1A grey10
        16: ( 27, 27, 27) #1B1B1B srgb(27,27,27)
        13: ( 28, 28, 28) #1C1C1C grey11
        13: ( 29, 29, 29) #1D1D1D srgb(29,29,29)
        15: ( 30, 30, 30) #1E1E1E srgb(30,30,30)
        17: ( 31, 31, 31) #1F1F1F grey12
        16: ( 32, 32, 32) #202020 srgb(32,32,32)
        24: ( 33, 33, 33) #212121 grey13
        20: ( 34, 34, 34) #222222 srgb(34,34,34)
        31: ( 35, 35, 35) #232323 srgb(35,35,35)
        28: ( 36, 36, 36) #242424 grey14
        30: ( 37, 37, 37) #252525 srgb(37,37,37)
        36: ( 38, 38, 38) #262626 grey15
        29: ( 39, 39, 39) #272727 srgb(39,39,39)
        28: ( 40, 40, 40) #282828 srgb(40,40,40)
        45: ( 41, 41, 41) #292929 grey16
        42: ( 42, 42, 42) #2A2A2A srgb(42,42,42)
        36: ( 43, 43, 43) #2B2B2B grey17
        33: ( 44, 44, 44) #2C2C2C srgb(44,44,44)
        36: ( 45, 45, 45) #2D2D2D srgb(45,45,45)
        40: ( 46, 46, 46) #2E2E2E grey18
        43: ( 47, 47, 47) #2F2F2F srgb(47,47,47)
        36: ( 48, 48, 48) #303030 grey19
        50: ( 49, 49, 49) #313131 srgb(49,49,49)
        42: ( 50, 50, 50) #323232 srgb(50,50,50)
        37: ( 51, 51, 51) #333333 grey20
        30: ( 52, 52, 52) #343434 srgb(52,52,52)
        40: ( 53, 53, 53) #353535 srgb(53,53,53)
        45: ( 54, 54, 54) #363636 grey21
        33: ( 55, 55, 55) #373737 srgb(55,55,55)
        38: ( 56, 56, 56) #383838 grey22
        31: ( 57, 57, 57) #393939 srgb(57,57,57)
        30: ( 58, 58, 58) #3A3A3A srgb(58,58,58)
        49: ( 59, 59, 59) #3B3B3B grey23
        41: ( 60, 60, 60) #3C3C3C srgb(60,60,60)
        35: ( 61, 61, 61) #3D3D3D grey24
        39: ( 62, 62, 62) #3E3E3E srgb(62,62,62)
        43: ( 63, 63, 63) #3F3F3F srgb(63,63,63)
        25: ( 64, 64, 64) #404040 grey25
        26: ( 65, 65, 65) #414141 srgb(65,65,65)
        30: ( 66, 66, 66) #424242 grey26
        22: ( 67, 67, 67) #434343 srgb(67,67,67)
        25: ( 68, 68, 68) #444444 srgb(68,68,68)
        26: ( 69, 69, 69) #454545 grey27
        21: ( 70, 70, 70) #464646 srgb(70,70,70)
        24: ( 71, 71, 71) #474747 grey28
        15: ( 72, 72, 72) #484848 srgb(72,72,72)
        25: ( 73, 73, 73) #494949 srgb(73,73,73)
        22: ( 74, 74, 74) #4A4A4A grey29
        18: ( 75, 75, 75) #4B4B4B srgb(75,75,75)
        30: ( 76, 76, 76) #4C4C4C srgb(76,76,76)
        19: ( 77, 77, 77) #4D4D4D grey30
        15: ( 78, 78, 78) #4E4E4E srgb(78,78,78)
        21: ( 79, 79, 79) #4F4F4F grey31
        31: ( 80, 80, 80) #505050 srgb(80,80,80)
        24: ( 81, 81, 81) #515151 srgb(81,81,81)
        24: ( 82, 82, 82) #525252 grey32
        26: ( 83, 83, 83) #535353 srgb(83,83,83)
        25: ( 84, 84, 84) #545454 grey33
        31: ( 85, 85, 85) #555555 srgb(85,85,85)
        31: ( 86, 86, 86) #565656 srgb(86,86,86)
        32: ( 87, 87, 87) #575757 grey34
        43: ( 88, 88, 88) #585858 srgb(88,88,88)
        29: ( 89, 89, 89) #595959 grey35
        40: ( 90, 90, 90) #5A5A5A srgb(90,90,90)
        33: ( 91, 91, 91) #5B5B5B srgb(91,91,91)
        42: ( 92, 92, 92) #5C5C5C grey36
        37: ( 93, 93, 93) #5D5D5D srgb(93,93,93)
        45: ( 94, 94, 94) #5E5E5E grey37
        55: ( 95, 95, 95) #5F5F5F srgb(95,95,95)
        34: ( 96, 96, 96) #606060 srgb(96,96,96)
        34: ( 97, 97, 97) #616161 grey38
        39: ( 98, 98, 98) #626262 srgb(98,98,98)
        45: ( 99, 99, 99) #636363 grey39
        44: (100,100,100) #646464 srgb(100,100,100)
        48: (101,101,101) #656565 srgb(101,101,101)
        39: (102,102,102) #666666 grey40
        47: (103,103,103) #676767 srgb(103,103,103)
        41: (104,104,104) #686868 srgb(104,104,104)
        57: (105,105,105) #696969 DimGray
        48: (106,106,106) #6A6A6A srgb(106,106,106)
        58: (107,107,107) #6B6B6B grey42
        63: (108,108,108) #6C6C6C srgb(108,108,108)
        61: (109,109,109) #6D6D6D srgb(109,109,109)
        58: (110,110,110) #6E6E6E grey43
        73: (111,111,111) #6F6F6F srgb(111,111,111)
        80: (112,112,112) #707070 grey44
        66: (113,113,113) #717171 srgb(113,113,113)
        58: (114,114,114) #727272 srgb(114,114,114)
        74: (115,115,115) #737373 grey45
        70: (116,116,116) #747474 srgb(116,116,116)
        76: (117,117,117) #757575 grey46
        68: (118,118,118) #767676 srgb(118,118,118)
        62: (119,119,119) #777777 srgb(119,119,119)
        59: (120,120,120) #787878 grey47
        70: (121,121,121) #797979 srgb(121,121,121)
        71: (122,122,122) #7A7A7A grey48
        57: (123,123,123) #7B7B7B srgb(123,123,123)
        54: (124,124,124) #7C7C7C srgb(124,124,124)
        65: (125,125,125) #7D7D7D grey49
        68: (126,126,126) #7E7E7E gray
        66: (127,127,127) #7F7F7F grey50
        64: (128,128,128) #808080 fractal
        67: (129,129,129) #818181 srgb(129,129,129)
        72: (130,130,130) #828282 grey51
        64: (131,131,131) #838383 srgb(131,131,131)
        72: (132,132,132) #848484 srgb(132,132,132)
        83: (133,133,133) #858585 grey52
        57: (134,134,134) #868686 srgb(134,134,134)
        69: (135,135,135) #878787 grey53
        58: (136,136,136) #888888 srgb(136,136,136)
        74: (137,137,137) #898989 srgb(137,137,137)
        69: (138,138,138) #8A8A8A grey54
        64: (139,139,139) #8B8B8B srgb(139,139,139)
        68: (140,140,140) #8C8C8C grey55
        72: (141,141,141) #8D8D8D srgb(141,141,141)
        93: (142,142,142) #8E8E8E srgb(142,142,142)
        79: (143,143,143) #8F8F8F grey56
        74: (144,144,144) #909090 srgb(144,144,144)
        80: (145,145,145) #919191 grey57
       106: (146,146,146) #929292 srgb(146,146,146)
        93: (147,147,147) #939393 srgb(147,147,147)
        70: (148,148,148) #949494 grey58
        87: (149,149,149) #959595 srgb(149,149,149)
        83: (150,150,150) #969696 grey59
       101: (151,151,151) #979797 srgb(151,151,151)
        81: (152,152,152) #989898 srgb(152,152,152)
        84: (153,153,153) #999999 grey60
       109: (154,154,154) #9A9A9A srgb(154,154,154)
       101: (155,155,155) #9B9B9B srgb(155,155,155)
        93: (156,156,156) #9C9C9C grey61
        98: (157,157,157) #9D9D9D srgb(157,157,157)
        84: (158,158,158) #9E9E9E grey62
        96: (159,159,159) #9F9F9F srgb(159,159,159)
        85: (160,160,160) #A0A0A0 srgb(160,160,160)
        80: (161,161,161) #A1A1A1 grey63
        79: (162,162,162) #A2A2A2 srgb(162,162,162)
       107: (163,163,163) #A3A3A3 grey64
        68: (164,164,164) #A4A4A4 srgb(164,164,164)
        73: (165,165,165) #A5A5A5 srgb(165,165,165)
        73: (166,166,166) #A6A6A6 grey65
        71: (167,167,167) #A7A7A7 srgb(167,167,167)
        96: (168,168,168) #A8A8A8 grey66
        69: (169,169,169) #A9A9A9 DarkGray
        84: (170,170,170) #AAAAAA srgb(170,170,170)
        88: (171,171,171) #ABABAB grey67
        82: (172,172,172) #ACACAC srgb(172,172,172)
       101: (173,173,173) #ADADAD grey68
        79: (174,174,174) #AEAEAE srgb(174,174,174)
        54: (175,175,175) #AFAFAF srgb(175,175,175)
        86: (176,176,176) #B0B0B0 grey69
        61: (177,177,177) #B1B1B1 srgb(177,177,177)
        70: (178,178,178) #B2B2B2 srgb(178,178,178)
        52: (179,179,179) #B3B3B3 grey70
        52: (180,180,180) #B4B4B4 srgb(180,180,180)
        63: (181,181,181) #B5B5B5 grey71
        58: (182,182,182) #B6B6B6 srgb(182,182,182)
        70: (183,183,183) #B7B7B7 srgb(183,183,183)
        54: (184,184,184) #B8B8B8 grey72
        52: (185,185,185) #B9B9B9 srgb(185,185,185)
        48: (186,186,186) #BABABA grey73
        56: (187,187,187) #BBBBBB srgb(187,187,187)
        48: (188,188,188) #BCBCBC srgb(188,188,188)
        45: (189,189,189) #BDBDBD grey74
        48: (190,190,190) #BEBEBE grey
        54: (191,191,191) #BFBFBF grey75
        65: (192,192,192) #C0C0C0 silver
        61: (193,193,193) #C1C1C1 srgb(193,193,193)
        42: (194,194,194) #C2C2C2 grey76
        52: (195,195,195) #C3C3C3 srgb(195,195,195)
        50: (196,196,196) #C4C4C4 grey77
        49: (197,197,197) #C5C5C5 srgb(197,197,197)
        39: (198,198,198) #C6C6C6 srgb(198,198,198)
        54: (199,199,199) #C7C7C7 grey78
        48: (200,200,200) #C8C8C8 srgb(200,200,200)
        46: (201,201,201) #C9C9C9 grey79
        36: (202,202,202) #CACACA srgb(202,202,202)
        27: (203,203,203) #CBCBCB srgb(203,203,203)
        38: (204,204,204) #CCCCCC grey80
        43: (205,205,205) #CDCDCD srgb(205,205,205)
        35: (206,206,206) #CECECE srgb(206,206,206)
        56: (207,207,207) #CFCFCF grey81
        41: (208,208,208) #D0D0D0 srgb(208,208,208)
        67: (209,209,209) #D1D1D1 grey82
        42: (210,210,210) #D2D2D2 srgb(210,210,210)
        69: (211,211,211) #D3D3D3 LightGray
        59: (212,212,212) #D4D4D4 grey83
        76: (213,213,213) #D5D5D5 srgb(213,213,213)
        69: (214,214,214) #D6D6D6 grey84
        74: (215,215,215) #D7D7D7 srgb(215,215,215)
        68: (216,216,216) #D8D8D8 srgb(216,216,216)
        83: (217,217,217) #D9D9D9 grey85
        67: (218,218,218) #DADADA srgb(218,218,218)
        83: (219,219,219) #DBDBDB grey86
        62: (220,220,220) #DCDCDC gainsboro
        63: (221,221,221) #DDDDDD srgb(221,221,221)
        60: (222,222,222) #DEDEDE grey87
        63: (223,223,223) #DFDFDF srgb(223,223,223)
        74: (224,224,224) #E0E0E0 grey88
        65: (225,225,225) #E1E1E1 srgb(225,225,225)
        58: (226,226,226) #E2E2E2 srgb(226,226,226)
        72: (227,227,227) #E3E3E3 grey89
        83: (228,228,228) #E4E4E4 srgb(228,228,228)
       135: (229,229,229) #E5E5E5 grey90
       204: (230,230,230) #E6E6E6 srgb(230,230,230)
       130: (231,231,231) #E7E7E7 srgb(231,231,231)
        69: (232,232,232) #E8E8E8 grey91
        94: (233,233,233) #E9E9E9 srgb(233,233,233)
        50: (234,234,234) #EAEAEA srgb(234,234,234)
        43: (235,235,235) #EBEBEB grey92
        30: (236,236,236) #ECECEC srgb(236,236,236)
        26: (237,237,237) #EDEDED grey93
        20: (238,238,238) #EEEEEE srgb(238,238,238)
        26: (239,239,239) #EFEFEF srgb(239,239,239)
        20: (240,240,240) #F0F0F0 grey94
        23: (241,241,241) #F1F1F1 srgb(241,241,241)
        31: (242,242,242) #F2F2F2 grey95
        33: (243,243,243) #F3F3F3 srgb(243,243,243)
        34: (244,244,244) #F4F4F4 srgb(244,244,244)
        32: (245,245,245) #F5F5F5 grey96
        61: (246,246,246) #F6F6F6 srgb(246,246,246)
       375: (247,247,247) #F7F7F7 grey97
       353: (248,248,248) #F8F8F8 srgb(248,248,248)
       158: (249,249,249) #F9F9F9 srgb(249,249,249)
       145: (250,250,250) #FAFAFA grey98
       135: (251,251,251) #FBFBFB srgb(251,251,251)
       203: (252,252,252) #FCFCFC grey99
       340: (253,253,253) #FDFDFD srgb(253,253,253)
       621: (254,254,254) #FEFEFE srgb(254,254,254)
         1: (255,255,250) #FFFFFA srgb(255,255,250)
       410: (255,255,255) #FFFFFF white

[snibgo]

If you mean the names at the end like "grey9" or "srgb(24,24,24)", I would ignore them. For each colour, IM looks to see if it has a name. If it has, like "grey9", it writes the name.

[konstantin]

Problem solved, I had to apply options:

Code: Select all

 -colorspace gray -type palette 

Spectre in 2 colours:
https://www.youtube.com/watch?v=ZCtWucorr7g

[konstantin]

Another animation by animating the threshold: