GIF 文件格式探索

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本文深入探讨了GIF动画文件的格式细节，包括Header、LogicalScreenDescriptor、GlobalColorTable等关键组成部分，并通过Ruby代码示例展示了如何解析这些部分。

mini fang

最近，我们cute 的数字图像处理老师让我们看看GIF 的文件格式，然后实现一个均衡化算法。我准备用Ruby 做一个，

但Ruby 对位的操作不如C。还好找到了bit-struct，一个用string 来存储二进制数据的库。

我们会在后面对左图分析。

与针对相片影像而设计的JPEG 不同，GIF 由于采用了8位压缩，最多只能处理256种颜色（至少标准是这样），故不宜于显示真彩图片。

其实GIF 设计得很优美，有三个部分构成：Header，Data Stream，Trailer。

6 Byte 的Header 包括GIF 签名和版本号：

class GIF_Header < BitStruct # GIF Header =begin 7 6 5 4 3 2 1 0 Field Name Type +---------------+ 0 | | Signature 3 Bytes +- -+ 1 | | +- -+ 2 | | +---------------+ 3 | | Version 3 Bytes +- -+ 4 | | +- -+ 5 | | +---------------+ =end text :sign, 24, "Signature" text :v, 24, "Version" def print puts "+#{"-"*40}+" puts self.inspect_detailed puts "+#{"-"*40}+" end end

GIF 文件终结符是0x3b。

=begin 7 6 5 4 3 2 1 0 Field Name Type +---------------+ 0 | | GIF Trailer Byte +---------------+ =end

Data Stream由7 Byte 的Logical Screen Descriptor、Global Color Table（即调色板，可能是256×3 Byte，因为GIF 只能显示256色）以及多张图片组成。每张图片都有Image Descriptor，可能还有数据块和一些扩展模块。数据块包括Local Color Table 和Table Based Image Data。扩展模块有：Graphic Control Extension，Plain Text Extension，Comment Extension，Applicaton Extension。

Logical Screen Descriptor ：

class GIF_LSD < BitStruct # Logical Screen Descriptor =begin 7 6 5 4 3 2 1 0 Field Name Type +---------------+ 0 | | Logical Screen Width Unsigned +- -+ 1 | | +---------------+ 2 | | Logical Screen Height Unsigned +- -+ 3 | | +---------------+ 4 | | | | | <Packed Fields> See below +---------------+ 5 | | Background Color Index Byte +---------------+ 6 | | Pixel Aspect Ratio Byte +---------------+ =end unsigned :log_w, 16, "Logical Screen Width" unsigned :log_h, 16, "Logical Screen Height" hex_octets :h_bits, 8, "<Packed Fields>" unsigned :h_idx, 8, "Background Color Index" unsigned :radio, 8, "Pixel Aspect Ratio" def print_packed_fields(pf) $global_color_table_flag = pf[7] p "Global Color Table Flag = #{$global_color_table_flag}" cr = (pf[6] << 2) | (pf[5] << 1) | pf[4] p "Color Resolution = #{cr}" p "Sort Flag = #{pf[3]}" val = (pf[2] << 2) | (pf[1] << 1) | pf[0] p "Size of Global Color Table = #{val}" $size_of_gct = 3 * 2 ** (val+1) ar = (self.radio + 15) / 64 p "Aspect Ratio = #{ar}" if self.radio != 0 end def print puts "+#{"-"*40}+" puts self.inspect_detailed self.print_packed_fields Integer("0x" << self.h_bits) puts "+#{"-"*40}+" end end

Global Color Table ：

class GIF_GCT < BitStruct # Global Color Table($size_of_gct x 3 bytes) if $global_color_table_flag is one =begin 7 6 5 4 3 2 1 0 Field Name Type +===============+ 0 | | Red 0 Byte +- -+ 1 | | Green 0 Byte +- -+ 2 | | Blue 0 Byte +- -+ 3 | | Red 1 Byte +- -+ | | Green 1 Byte +- -+ up | | +- . . . . -+ ... to | | +- -+ | | Green 255 Byte +- -+ 767 | | Blue 255 Byte +===============+ =end rest :GCT, "Global Color Table" def print b = [] self.GCT.each_byte { |byte| b << byte } puts "+#{"-"*40}+" puts "Global Color Table:" (b.size/3).times do |idx| printf("color #{idx} black: 0x%02x, 0x%02x, 0x%02x/n", b[3*idx], b[3*idx+1], b[3*idx+2]) end puts "+#{"-"*40}+" end end

Image Descriptor：

Local Color Table：

class GIF_LCT < BitStruct # Local Color Table($size_of_lct x 3 bytes) if $local_color_table_flag is one =begin 7 6 5 4 3 2 1 0 Field Name Type +===============+ 0 | | Red 0 Byte +- -+ 1 | | Green 0 Byte +- -+ 2 | | Blue 0 Byte +- -+ 3 | | Red 1 Byte +- -+ | | Green 1 Byte +- -+ up | | +- . . . . -+ ... to | | +- -+ | | Green 255 Byte +- -+ 767 | | Blue 255 Byte +===============+ =end rest :LCT, "Local Color Table" def print b = [] self.LCT.each_byte { |byte| b << byte } (b.size/4).times do |idx| printf("#{idx}: 0x%02x, 0x%02x, 0x%02x, 0x%02x/n", b[4*idx], b[4*idx+1], b[4*idx+2], b[4*idx+3]) end end end

Table Based Image Data：

class GIF_TBID < BitStruct # Table Based Image Data =begin 7 6 5 4 3 2 1 0 Field Name Type +---------------+ | | LZW Minimum Code Size Byte +---------------+ +===============+ | | / / Image Data Data Sub-blocks | | +===============+ =end def print_data(file) code_size = Integer("0x" << Byte.new(file.read(1)).byte) puts "LZW Minimum Code Size = #{code_size}" while (blk_size = Integer("0x" << Byte.new(file.read(1)).byte)) != 0x00 puts "Block Size = #{blk_size}" data = file.read(blk_size) data.each_byte { |byte| printf "%02x, ", byte } p "/nblock size = #{data.size}" end printf "Block Terminator = 0x%02x/n", blk_size puts "+#{"-"*40}+" end end

Graphic Control Extension Block：

class GIF_GCEB < BitStruct # Graphic Control Extension Block =begin 7 6 5 4 3 2 1 0 Field Name Type +---------------+ 0 | | Extension Introducer Byte +---------------+ 1 | | Graphic Control Label Byte +---------------+ +---------------+ 0 | | Block Size Byte +---------------+ 1 | | | | | <Packed Fields> See below +---------------+ 2 | | Delay Time Unsigned +- -+ 3 | | +---------------+ 4 | | Transparent Color Index Byte +---------------+ +---------------+ 0 | | Block Terminator Byte +---------------+ =end # hex_octets :intro, 8, "Extension Introducer(0x21)" # hex_octets :label, 8, "Graphic Control Label(0xf9)" hex_octets :b_size, 8, "Block Size(0x04)" hex_octets :b_bits, 8, "<Packed Fields>" unsigned :time, 16, "Delay Time" unsigned :b_idx, 8, "Transparent Color Index" hex_octets :term, 8, "Block Terminator(0x00)" end

Comment Extension Block：

class GIF_CEB < BitStruct # Comment Extension Block =begin 7 6 5 4 3 2 1 0 Field Name Type +---------------+ 0 | | Extension Introducer Byte +---------------+ 1 | | Comment Label Byte +---------------+ +===============+ | | N | | Comment Data Data Sub-blocks | | +===============+ +---------------+ 0 | | Block Terminator Byte +---------------+ =end def print(file) printf "+#{"-"*18}0x%02x#{"-"*18}+/n", $intro puts "Comment Extension Block:" while (blk_size = Integer("0x" << Byte.new(file.read(1)).byte)) != 0x00 puts "Block Size = #{blk_size}" pp data = file.read(blk_size) end puts "+#{"-"*40}+" end end

Plain Text Extension Block：

class GIF_PTEB < BitStruct # Plain Text Extension Block =begin 7 6 5 4 3 2 1 0 Field Name Type +---------------+ 0 | | Extension Introducer Byte +---------------+ 1 | | Plain Text Label Byte +---------------+ +---------------+ 0 | | Block Size Byte +---------------+ 1 | | Text Grid Left Position Unsigned +- -+ 2 | | +---------------+ 3 | | Text Grid Top Position Unsigned +- -+ 4 | | +---------------+ 5 | | Text Grid Width Unsigned +- -+ 6 | | +---------------+ 7 | | Text Grid Height Unsigned +- -+ 8 | | +---------------+ 9 | | Character Cell Width Byte +---------------+ 10 | | Character Cell Height Byte +---------------+ 11 | | Text Foreground Color Index Byte +---------------+ 12 | | Text Background Color Index Byte +---------------+ +===============+ | | N | | Plain Text Data Data Sub-blocks | | +===============+ +---------------+ 0 | | Block Terminator Byte +---------------+ =end # hex_octets :x_intro, 8, "Extension Introducer(0x21)" # hex_octets :label, 8, "Plain Text Label(0x01)" unsigned :blk_size, 8, "Block Size(0x0c)" unsigned :left, 16, "Text Grid Left Position" unsigned :top, 16, "Text Grid Top Position" unsigned :g_w, 16, "Text Grid Width" unsigned :g_h, 16, "Text Grid Height" unsigned :c_w, 8, "Character Cell Width" unsigned :c_h, 8, "Character Cell Height" unsigned :fore, 8, "Text Foreground Color Index" unsigned :back, 8, "Text Background Color Index" #hex_octets :term, 8, "Block Terminator(0x00)" def print file printf "+#{"-"*18}0x%02x#{"-"*18}+/n", $intro puts "Plain Text Extension Block:" teb = GIF_TEB.new(file.read(13)) puts self.inspect_detailed while (blk_size = Integer("0x" << Byte.new(file.read(1)).byte)) != 0x00 puts "Block Size = #{blk_size}" pp data = f.read(blk_size) end puts "+#{"-"*40}+" end end

Application Extension Block：

class GIF_AEB < BitStruct # Application Extension Block =begin 7 6 5 4 3 2 1 0 Field Name Type +---------------+ 0 | | Extension Introducer Byte +---------------+ 1 | | Extension Label Byte +---------------+ +---------------+ 0 | | Block Size Byte +---------------+ 1 | | +- -+ 2 | | +- -+ 3 | | Application Identifier 8 Bytes +- -+ 4 | | +- -+ 5 | | +- -+ 6 | | +- -+ 7 | | +- -+ 8 | | +---------------+ 9 | | +- -+ 10 | | Appl. Authentication Code 3 Bytes +- -+ 11 | | +---------------+ +===============+ | | | | Application Data Data Sub-blocks | | | | +===============+ +---------------+ 0 | | Block Terminator Byte +---------------+ =end # hex_octets :x_intro, 8, "Extension Introducer(0x21)" # hex_octets :label, 8, "Application Label(0xff)" unsigned :blk_size, 8, "Block Size(0x0b)" text :id, 64, "Application Identifire" def print(file) printf "+#{"-"*18}0x%02x#{"-"*18}+/n", $intro puts "Application Extension Block:" puts self.inspect_detailed while (blk_size = Integer("0x" << Byte.new(file.read(1)).byte)) != 0x00 puts "Block Size = #{blk_size}" pp data = file.read(blk_size) end puts "+#{"-"*40}+" end end

GIF 有两个标准87a（即87版）和89a（即89版）。GIF 89a 只是在87a 的基础上扩充了一点支持动画的功能。
87a 包括GIF Header，Image Block，Trailer 三个部分。而89a包括GIF Header，Graphic Control Extension，Image Block，Trailer 四个部分。

GIF 最大的特点就是支持动画。其实GIF Animation 的格式差不多，也分为四部分：GIF Header，Application Extension，任意个Graphic Control Extension Image Block，Trailer。

由于BitStruct 其实是一个String，我需要一个辅助类来转换成十六进制数。

class Byte < BitStruct hex_octets :byte, 8 end

首先，对Header 分析。

path = "f:/gif/dobry.gif" f = File.open(path, "rb") # note: it must be opened in binary mode. header = GIF_Header.new(f.read(6)) header.print

接着是分析Logical Screen Descriptor 的各个字段。

lsd = GIF_LSD.new(f.read(7)) lsd.print

根据Logical Screen Descriptor 的Logical Screen Descriptor 判断是否存在全局调色板。

if $global_color_table_flag == 1 gct = GIF_GCT.new(f.read($size_of_gct)) gct.print end

接下来是处理图片，看流程图：

GIF 处理的流程图

$intro = -1 $Trailer = 0x3b while ($intro = Integer("0x" << Byte.new(f.read(1)).byte)) != $Trailer if $intro == 0x2c # Image Descriptor id = GIF_ID.new(f.read(9)) id.print if $local_color_table_flag == 1 lct = GIF_LCT.new(f.read($size_of_lct)) lct.print_lct end tbid = GIF_TBID.new tbid.print_data f elsif $intro == 0x21 case Integer("0x" << Byte.new(f.read(1)).byte) when 0xf9: gceb = GIF_GCEB.new(f.read(6)) gceb.print when 0xfe: ceb = GIF_CEB.new ceb.print f when 0x01: pteb = GIF_PTEB.new pteb.print f when 0xff: aeb = GIF_AEB.new(f.read(11)) aeb.print f else # ... end else printf "error: 0x%02x/n", $intro break end end printf "+#{"-"*18}0x%02x#{"-"*18}+/n", $intro printf "Trailer(0x3b) = 0x%02x/n", $intro puts "+#{"-"*40}+" f.close

这里是完整源码。

输出：

=begin +----------------------------------------+ GIF_Header: Signature = "GIF" Version = "89a" +----------------------------------------+ +----------------------------------------+ GIF_LSD: Logical Screen Width = 12800 Logical Screen Height = 13056 <Packed Fields> = "d1" Background Color Index = 0 Pixel Aspect Ratio = 0 "Global Color Table Flag = 1" "Color Resolution = 5" "Sort Flag = 0" "Size of Global Color Table = 1" +----------------------------------------+ +----------------------------------------+ Global Color Table: color 0 black: 0x00, 0x00, 0x00 color 1 black: 0xff, 0xff, 0xff color 2 black: 0x00, 0x00, 0x00 color 3 black: 0x00, 0x00, 0x00 +----------------------------------------+ +------------------0x21------------------+ Comment Extension Block: Block Size = 194 "http://www.rtlsoft.com/animagic//n/nCreated with Animagic GIF V 1.22a/nby Right to Left Software Inc./n/nTo suppress this message in the registered version/nuncheck /"Options | Animagic comment frame/"/n" +----------------------------------------+ +------------------0x21------------------+ Graphic Control Extension Block: GIF_GCEB: Block Size(0x04) = "04" <Packed Fields> = "00" Delay Time = 6400 Transparent Color Index = 0 Block Terminator(0x00) = "00" +----------------------------------------+ +------------------0x2c------------------+ GIF_ID: Image Left Position = 0 Image Top Position = 0 Image Width = 12800 Image Height = 12800 <Packed Fields> = "00" "Local Color Table Flag, 0" "Interlace Flag = 0" "Sort Flag = 0" "Size of Local Color Table = 0" LZW Minimum Code Size = 2 Block Size = 203 84, 8f, 16, cb, ed, 1f, 40, 4c, b4, 52, 88, f3, b4, 3c, e9, 8f, 75, 1d, 48, 3e, 97, 58, a6, 9b, 78, a9, 1f, 3b, ba, 19, 1c, cb, 21, dd, da, 10, bd, 2a, fa, 8c, 43, fc, 80, 41, df, 70, 57, 94, 1c, 91, a3, ca, d2, 94, 54, 3e, 1b, d1, a9, 23, 2a, 25, 1d, a8, d0, 64, 6a, cb, cd, 62, b5, e0, 85, c7, 8c, cd, 32, d4, 67, e7, 04, 8d, bb, 1a, e1, a8, 5e, 90, 5a, 06, 86, d3, 74, 5d, 7a, 3e, f4, 97, f7, 23, 08, 68, 53, 68, 88, 44, 24, e4, 55, a2, 46, 57, f8, 22, 24, 87, f8, 08, 39, 78, c9, 77, 65, 77, 53, 69, b9, d2, e9, 29, e3, 79, e6, 42, 3a, c9, 54, 76, 0a, 78, b2, 91, c9, 58, b5, 96, ea, 63, f1, ca, 22, 2b, c9, 81, d7, a8, 27, 9b, 63, 5b, a7, e2, b6, 16, eb, f8, 4b, 5c, 4c, 86, ba, cb, 0b, 52, 4a, 39, a6, 9c, 88, e8, 8c, 09, 5c, a4, b1, cc, 1c, 19, ba, a8, b9, e8, 9d, dc, 95, 88, 1c, bd, 09, 99, 0d, 53, 00, "/nblock size = 203" Block Terminator = 0x00 +----------------------------------------+ +------------------0x21------------------+ Graphic Control Extension Block: GIF_GCEB: Block Size(0x04) = "04" <Packed Fields> = "00" Delay Time = 6400 Transparent Color Index = 0 Block Terminator(0x00) = "00" +----------------------------------------+ +------------------0x2c------------------+ GIF_ID: Image Left Position = 0 Image Top Position = 512 Image Width = 12800 Image Height = 12544 <Packed Fields> = "00" "Local Color Table Flag, 0" "Interlace Flag = 0" "Sort Flag = 0" "Size of Local Color Table = 0" LZW Minimum Code Size = 2 Block Size = 251 8c, 8f, a9, 1b, 00, 0c, a3, 34, 6e, bd, 89, 73, b3, f6, ea, e4, 81, e1, 51, 89, 9f, e2, 8c, 54, 67, 9e, a8, da, a8, 25, 35, bb, 48, 4d, 32, 5e, 6a, b3, 24, de, 81, f5, 64, a1, 8b, 11, 28, e1, e9, 50, af, 18, 32, f9, 5c, 8a, 94, 2e, 6a, f3, b7, 4b, 45, 27, 5a, e8, b4, db, 73, 96, 88, 37, ad, b5, 6a, ae, cc, d2, 6c, e1, 27, 2d, 86, b3, c3, 5f, 1a, ae, ed, 3e, cd, 8b, ea, 39, 1d, db, 77, 84, b7, a5, 37, 68, f8, f7, 65, 56, e6, 87, 08, d8, c5, 83, d7, e8, 08, 96, 98, 67, 03, 17, b3, 11, 47, 58, 78, b8, 69, a9, f1, 20, a7, f8, 09, 1a, 3a, ba, c6, 88, d8, b7, b8, 48, ba, 7a, 76, f7, 09, 92, c3, 05, 69, 29, a8, d4, 86, f1, 48, 24, ba, 5b, 6a, da, 5b, b9, 3b, 68, 3b, 96, 6a, c8, 3a, 0c, 95, 95, 3b, e9, 09, 0a, 96, ac, 3c, 9a, d9, fc, 4a, 75, 5b, cd, 09, fc, 82, cc, 8d, fd, 2a, ee, 19, 14, 79, 5c, ad, 93, be, 42, 5c, ee, 1a, cd, c7, 4d, 09, bd, 27, ff, 7b, 6e, 77, 68, 1f, 88, 1f, 1e, bc, af, 08, 20, 3f, 81, 01, e7, 45, fb, 47, 50, 99, 13, 5a, 02, 37, 24, 8c, 17, 4e, 94, 26, 7d, 0f, 23, 69, 29, 00, "/nblock size = 251" Block Terminator = 0x00 +----------------------------------------+ +------------------0x21------------------+ Graphic Control Extension Block: GIF_GCEB: Block Size(0x04) = "04" <Packed Fields> = "00" Delay Time = 6400 Transparent Color Index = 0 Block Terminator(0x00) = "00" +----------------------------------------+ +------------------0x2c------------------+ GIF_ID: Image Left Position = 0 Image Top Position = 256 Image Width = 12032 Image Height = 12544 <Packed Fields> = "00" "Local Color Table Flag, 0" "Interlace Flag = 0" "Sort Flag = 0" "Size of Local Color Table = 0" LZW Minimum Code Size = 2 Block Size = 230 8c, 8f, a9, cb, ed, 7f, 80, 9c, 12, 5a, 47, 73, 05, b7, 1b, ae, 85, 95, 87, 45, a2, 48, 5a, e7, 99, 3e, eb, 14, 68, 2d, 32, 52, f1, 6b, cf, f7, d8, ac, 7a, 06, 61, b5, 64, 2a, 94, 27, 74, 24, 5e, 90, 29, 65, 10, c8, 5b, 3a, 19, 20, 63, b2, ca, 79, 4e, a5, 39, 17, 6e, 41, b4, 65, bd, b8, 5a, 17, 3b, c6, 94, 77, a6, 33, 90, 8a, f6, c1, 76, 73, 7a, 34, 51, 16, 47, b3, 3c, 58, 9a, e6, f3, c1, 57, a7, 06, b7, 06, 78, 67, 18, d1, 76, 68, 57, f4, 66, f7, 22, d8, a5, b6, 31, 96, d7, a7, f7, 07, 76, c3, 78, 68, 55, 92, 99, 87, b8, 49, 65, 28, 27, ba, d4, f3, 45, 58, ea, 85, 87, a9, b3, 08, cb, 4a, eb, 57, 69, db, 48, d8, 09, b6, 1b, cb, c8, 75, 37, 1a, 23, 48, fc, b8, 19, 6b, d9, 41, e9, 89, ca, 7b, dc, bb, 06, 59, e8, 1a, f9, fb, 5a, 89, c9, cc, 49, 86, 24, c9, 1d, 0c, 19, 38, 97, 98, bd, 6d, 5d, bd, cc, 74, 2a, db, 5c, ae, 50, 9d, 9e, 7b, ae, d2, 13, bd, 1e, 1e, 3d, 3f, dd, bd, eb, 38, 29, a4, 9f, b6, 00, 05, 00, "/nblock size = 230" Block Terminator = 0x00 +----------------------------------------+ +------------------0x21------------------+ Graphic Control Extension Block: GIF_GCEB: Block Size(0x04) = "04" <Packed Fields> = "00" Delay Time = 6400 Transparent Color Index = 0 Block Terminator(0x00) = "00" +----------------------------------------+ +------------------0x2c------------------+ GIF_ID: Image Left Position = 0 Image Top Position = 0 Image Width = 12800 Image Height = 12800 <Packed Fields> = "00" "Local Color Table Flag, 0" "Interlace Flag = 0" "Sort Flag = 0" "Size of Local Color Table = 0" LZW Minimum Code Size = 2 Block Size = 232 0c, 8e, a9, cb, ed, 0f, a3, 9c, b4, da, 8b, 4c, d8, 1a, 63, 0e, 86, a2, f7, 88, e6, 49, 1e, e7, 6a, a6, 2a, 0b, 6f, 2e, 10, c7, 33, 5d, b3, 77, ae, cf, 7c, bf, 90, 49, 7e, 2b, 46, 68, 48, 1c, 29, 5a, 91, a4, 86, b3, 44, 95, 92, 38, 61, 46, 3a, 75, 42, af, 58, 47, b1, 96, 28, 36, b5, db, d7, d6, 9a, e5, 55, 0d, 5c, f6, 0b, 49, 6e, cb, c7, 71, b3, 3b, 43, 87, fe, b8, a4, fd, 9a, 0d, d2, a7, a6, 44, 58, 71, 24, 76, f4, 57, 16, 96, 06, a3, 68, 97, 68, d6, a8, 33, e2, 68, e7, 05, f6, 08, a4, 14, 14, f8, 15, a8, 98, 69, a4, 87, 12, e9, d4, e0, 29, 1a, 6a, 83, 4a, 6a, d9, a6, 36, 2a, f3, fa, 94, 79, 87, 0a, 0b, 8a, b7, ca, 79, a1, db, 19, 6b, 38, 44, c3, db, 3b, 86, b3, 1b, 96, 5a, 48, 51, 5b, 9b, ac, da, 0c, 89, 66, c5, 6a, e1, fc, 4b, 0d, d4, dc, 25, 99, cb, 24, dd, 08, 6c, 4c, 87, f9, ab, 0c, 0e, 71, ce, 18, 29, bb, 68, 7e, d6, 21, 76, f3, b8, 8b, 8d, e6, 82, 05, 88, 4d, 9c, bf, 4d, 9c, 4e, d0, a6, 7e, f2, 6e, 14, 00, "/nblock size = 232" Block Terminator = 0x00 +----------------------------------------+ +------------------0x21------------------+ Graphic Control Extension Block: GIF_GCEB: Block Size(0x04) = "04" <Packed Fields> = "00" Delay Time = 6400 Transparent Color Index = 0 Block Terminator(0x00) = "00" +----------------------------------------+ +------------------0x2c------------------+ GIF_ID: Image Left Position = 0 Image Top Position = 0 Image Width = 12800 Image Height = 12800 <Packed Fields> = "00" "Local Color Table Flag, 0" "Interlace Flag = 0" "Sort Flag = 0" "Size of Local Color Table = 0" LZW Minimum Code Size = 2 Block Size = 190 8c, 8f, a9, cb, ed, cf, 00, 9c, 74, 81, 8b, 73, dd, 36, 7b, cd, 55, df, e8, 85, 13, 49, 9a, 27, 3a, 06, 98, 1a, 95, 9f, 02, c2, 47, bb, 49, b6, 3b, 87, ba, 8a, f3, fd, 84, 2f, db, 30, 57, 83, 1d, 29, 3d, e3, 12, d2, 54, 3e, 1f, 51, 25, b1, b8, bb, 70, 4a, 3b, 83, 76, 9b, 94, 5e, a7, 60, e0, 97, 86, bd, a1, 4c, e7, 4e, 1b, c4, 15, f1, c8, 73, 5d, 33, 4d, 8d, 27, ee, 2d, bc, c3, de, e6, a5, 71, a4, 95, b2, 52, 35, 46, a7, f6, 12, 68, d6, e8, f6, a3, c8, e4, 17, f3, 28, 65, 89, e6, d2, 85, 10, f6, b7, b9, 47, f9, 69, 01, aa, 29, 8a, a6, c7, 63, fa, 17, 26, 49, 25, c2, 9a, 75, 58, 67, aa, 28, d3, 69, b4, ba, 46, 5b, 79, da, 2a, 07, 86, c9, 46, b4, 2b, 44, eb, cb, a9, 5a, 9a, 93, cc, 6c, e5, d5, 1b, dc, c5, 82, c8, 3c, 1d, fd, 69, 7d, ec, 34, 5d, 51, 00, "/nblock size = 190" Block Terminator = 0x00 +----------------------------------------+ +------------------0x3b------------------+ Trailer(0x3b) = 0x3b +----------------------------------------+ =end

可以看出这幅gif 图像有15个模块，掐头去尾共5幅画：

five persons