TGA file format (waveform sound file format)

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Tga Common formats are uncompressed RGB And compression RGB Two formats , The third of the document Byte Bit as a marker ：2 Is uncompressed RGB Format ,10 For compression RGB Format . The classes here only implement reading in uncompressed format tga file .

Given first tga The file format of the file :

name		The offset	length	explain
Length of image information field		0	1	This field is 1 Byte unsigned integer , Point out the image information field （ See the back of this sub table ） length , Its value range is 0 To 255 , When it's for 0 When there is no image information field .
Color table type		1	1	0 Indicates that there is no color table ,1 Indicates that the color table exists . Because this format has no color table , Therefore, this item is usually ignored .
Image type code		2	1	This field is always 2 , This is also the format of this type 2 Why .
Color table specification field	The first address of the color table	3	2	The entry index at the beginning of the color table , integer （ Low position - High position ）	If the color table field is 0, Then ignore the field
	The length of the color table	5	2	The total number of items in the color table , integer （ Low position – High position ）
	Number of color table entries	7	1	digit （bit）,16 representative 16 position TGA ,24 representative 24 position TGA ,32 representative 32 position TGA
Image specification field	Images X Coordinate starting position	8	2	Lower left corner of the image X Integer of coordinates （ Low position – High position ） value
	Images Y Coordinate starting position	10	2	Lower left corner of the image Y Integer of coordinates （ Low position – High position ） value
	The width of the image	12	2	In pixels , Integer of image width （ Low position – High position ）
	Height of the image	14	2	In pixels , Integer of image width （ Low position – High position ）
	Image storage occupancy per pixel	16	2	Its value is 16,24 or 32 wait . Determines that the image is TGA 16,TGA24,TGA 32 wait .
	Image descriptor bytes	17	1	bits 3-0 – The number of attribute bits per pixel ; about TGA 16, The value is 0 or 1, about TGA 24, The value is 0, about TGA 32, The value is 8. bit 4 – Retain , It has to be for 0 bit 5 – Screen start position flag 0 = The origin is in the lower left corner 1 = Origin in the upper left corner about truevision The image must be 0 bits 7-6 – Cross data storage flag 00 = No cross 01 = Two roads / Even crossing 10 = Four way intersection 11 = Retain
Image information field		18	variable	Contains a free-form , The length of the image is determined by “ Image information field ” Appoint . It is often overlooked （ That is, offset 0 The value at is 0 ）, Note that it can contain 255 Characters . If you need to store more information , It can be placed after the image data .
Color table data		variable	variable	If the color table type is 0, Then the domain does not exist , Otherwise, read the number of bytes of each item in the image color table specification directly across this field , by 2,3,4 One of .
Image data		variable	variable	RGB Color data , The storage order is ：BBB GGG RRR (AAA)

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