我有一个透明区域（矩形）的图像。 我需要检测左上角透明像素的坐标和右下角像素的坐标。 如何用imagemagick或ruby做到这一点？
答案 0 :(得分：1)
图像magick identify command使用选项-verbose -alpha应该打印您需要的信息。
devin@debian-desktop-1:~$ identify -verbose -alpha Extract http://upload.wikimedia.org/wikipedia/commons/5/51/Google.png
Image: /tmp/magick-XXy36tWu
Base filename: Google.png
Format: PNG (Portable Network Graphics)
Class: DirectClass
Geometry: 1192x432+0+0
Resolution: 28.35x28.35
Print size: 42.0459x15.2381
Units: PixelsPerCentimeter
Type: Grayscale
Base type: Grayscale
Endianess: Undefined
Colorspace: RGB
Depth: 8-bit
Channel depth:
gray: 8-bit
Channel statistics:
Gray:
min: 0 (0)
max: 255 (1)
mean: 78.1591 (0.306506)
standard deviation: 117.214 (0.459663)
kurtosis: -1.28542
skewness: 0.843321
Histogram:
350312: ( 0, 0, 0) #000000 black
66: ( 9, 9, 9) #090909 rgb(9,9,9)
182: ( 10, 10, 10) #0A0A0A grey4
2866: ( 11, 11, 11) #0B0B0B rgb(11,11,11)
177: ( 13, 13, 13) #0D0D0D grey5
113: ( 15, 15, 15) #0F0F0F grey6
50: ( 19, 19, 19) #131313 rgb(19,19,19)
138: ( 20, 20, 20) #141414 grey8
1902: ( 22, 22, 22) #161616 rgb(22,22,22)
149: ( 27, 27, 27) #1B1B1B rgb(27,27,27)
18: ( 28, 28, 28) #1C1C1C grey11
83: ( 30, 30, 30) #1E1E1E rgb(30,30,30)
50: ( 31, 31, 31) #1F1F1F grey12
631: ( 33, 33, 33) #212121 grey13
9: ( 38, 38, 38) #262626 grey15
53: ( 40, 40, 40) #282828 rgb(40,40,40)
11: ( 41, 41, 41) #292929 grey16
200: ( 44, 44, 44) #2C2C2C rgb(44,44,44)
24: ( 45, 45, 45) #2D2D2D rgb(45,45,45)
2: ( 47, 47, 47) #2F2F2F rgb(47,47,47)
11: ( 51, 51, 51) #333333 grey20
17: ( 54, 54, 54) #363636 grey21
148: ( 55, 55, 55) #373737 rgb(55,55,55)
5: ( 57, 57, 57) #393939 rgb(57,57,57)
10: ( 60, 60, 60) #3C3C3C rgb(60,60,60)
10: ( 61, 61, 61) #3D3D3D grey24
2: ( 66, 66, 66) #424242 grey26
119: ( 67, 67, 67) #434343 rgb(67,67,67)
1: ( 71, 71, 71) #474747 grey28
8: ( 75, 75, 75) #4B4B4B rgb(75,75,75)
79: ( 78, 78, 78) #4E4E4E rgb(78,78,78)
7: ( 81, 81, 81) #515151 rgb(81,81,81)
3: ( 82, 82, 82) #525252 grey32
1: ( 85, 85, 85) #555555 rgb(85,85,85)
66: ( 89, 89, 89) #595959 grey35
1: ( 90, 90, 90) #5A5A5A rgb(90,90,90)
7: ( 92, 92, 92) #5C5C5C grey36
5: ( 94, 94, 94) #5E5E5E grey37
50: (100,100,100) #646464 rgb(100,100,100)
4: (102,102,102) #666666 grey40
1: (104,104,104) #686868 rgb(104,104,104)
9: (105,105,105) #696969 DimGray
3: (107,107,107) #6B6B6B grey42
49: (111,111,111) #6F6F6F rgb(111,111,111)
2: (112,112,112) #707070 grey44
2: (120,120,120) #787878 grey47
4: (121,121,121) #797979 rgb(121,121,121)
44: (122,122,122) #7A7A7A grey48
1: (132,132,132) #848484 rgb(132,132,132)
42: (133,133,133) #858585 grey52
1: (134,134,134) #868686 rgb(134,134,134)
1: (135,135,135) #878787 grey53
3: (142,142,142) #8E8E8E rgb(142,142,142)
3: (143,143,143) #8F8F8F grey56
46: (144,144,144) #909090 rgb(144,144,144)
4: (150,150,150) #969696 grey59
2: (153,153,153) #999999 grey60
31: (155,155,155) #9B9B9B rgb(155,155,155)
1: (161,161,161) #A1A1A1 grey63
2: (163,163,163) #A3A3A3 grey64
2: (165,165,165) #A5A5A5 rgb(165,165,165)
25: (166,166,166) #A6A6A6 grey65
1: (170,170,170) #AAAAAA rgb(170,170,170)
2: (173,173,173) #ADADAD grey68
2: (174,174,174) #AEAEAE rgb(174,174,174)
30: (177,177,177) #B1B1B1 rgb(177,177,177)
3: (180,180,180) #B4B4B4 rgb(180,180,180)
21: (188,188,188) #BCBCBC rgb(188,188,188)
3: (194,194,194) #C2C2C2 grey76
1: (195,195,195) #C3C3C3 rgb(195,195,195)
1: (198,198,198) #C6C6C6 rgb(198,198,198)
23: (200,200,200) #C8C8C8 rgb(200,200,200)
1: (201,201,201) #C9C9C9 grey79
1: (204,204,204) #CCCCCC grey80
2: (208,208,208) #D0D0D0 rgb(208,208,208)
23: (211,211,211) #D3D3D3 LightGray
2: (214,214,214) #D6D6D6 grey84
2: (217,217,217) #D9D9D9 grey85
30: (222,222,222) #DEDEDE grey87
1: (225,225,225) #E1E1E1 rgb(225,225,225)
2: (227,227,227) #E3E3E3 grey89
1: (228,228,228) #E4E4E4 rgb(228,228,228)
24: (233,233,233) #E9E9E9 rgb(233,233,233)
1: (240,240,240) #F0F0F0 grey94
25: (244,244,244) #F4F4F4 rgb(244,244,244)
2: (245,245,245) #F5F5F5 grey96
1: (246,246,246) #F6F6F6 rgb(246,246,246)
156871: (255,255,255) #FFFFFF white
Rendering intent: Undefined
Gamma: 0.45454
Chromaticity:
red primary: (0.63999,0.33001)
green primary: (0.3,0.6)
blue primary: (0.15,0.05999)
white point: (0.31269,0.32899)
Interlace: None
Background color: white
Border color: rgb(223,223,223)
Matte color: grey74
Transparent color: black
Compose: Over
Page geometry: 1192x432+0+0
Dispose: Undefined
Iterations: 0
Compression: Zip
Orientation: Undefined
Properties:
date:create: 2011-06-03T16:04:15-07:00
date:modify: 2011-06-03T16:04:15-07:00
signature: 7e7bb49c70ea3ef7fec10871b5cf1650af0b072b6d5c997db85f8c69015d0345
Artifacts:
verbose: true
Tainted: True
Filesize: 243KB
Number pixels: 515KB
Pixels per second: 17.16MB
User time: 0.020u
Elapsed time: 0:01.030
Version: ImageMagick 6.6.0-4 2010-11-16 Q16 http://www.imagemagick.org
devin@debian-desktop-1:~$
此命令使Google logo具有透明背景并仅提取Alpha通道。然后它获取此图像的属性（preview）。并将它们输出到命令行。
