The document discusses the .bmp image file format. It describes the basic structure of a .bmp file, which includes a bitmap file header containing metadata like file type and size, a bitmap information header containing image width, height and color properties, an optional color table, and the pixel data stored from bottom to top in uncompressed form. It notes that while .bmp files have a large size, the format is simple, well-documented, and supports lossless compression. Common uses of the .bmp format include its simplicity and lack of patents.

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Forerunners in Technical Education
A seminar on
.bmp Image Data format
Presented By
Mahesh Pawar (121697010)

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Forerunners in Technical Education
Some Common Image Formats
- JPG : Used for most digital photos but “lossy”
- GIF : Best for line drawings. 256 colors maximum. No loss
- BMP : Bitmap. Every pixel stored individually
- TIF : Standard in many technical applications. No loss
- PNG : Lossless image format
- RAW : Data as captured by digital camera

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Test Image in Various Formats
- JPG 67 kb
- GIF 185 kb (256 colors, optimized)
- BMP 899 kb (640*479*3/1024 =
898.125)
- TIF 902 kb
- PNG 418 kb
- RAW 900 kb
Test Image (640 x 479 pixels)

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GIF Versus JPG
GIF: 11 kb JPG: 78 kb

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.bmp format
-BMP file format called as bitmap or DIB file format
-DIB in memory
-Pixel storage :
- Pixels are stored with colour depth of 1,4,8,16,24,32 bits/pixel
Uncompressed bitmap files are typically much larger than compressed
-Colour palette

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Bitmap File structure
- Bitmap-file Header
- Bitmap information Header
- Colour table
Fig. Bitmap File Format

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Bitmap file Header
uint 2 bytes Filetype
Dword 4 bytes File size in bytes
Uint 2 bytes Reserved
Uint 2 bytes Reserved
dword 4 bytes Offset to data in
bytes
- Contains information about type, size and layout of a bitmap file
- First two characters – BM (0x42 0x4D)
- Next four bytes – file size
- Next four bytes are unused
- Final four bytes are an offset

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Bitmap information header
-Specifies the dimensions, compression type, and colour format for the bitmap
-First four bytes are header size – 40 bytes followed by width and height of the image
-Next two bytes – 1 i.e. number of planes
-Next two bytes – number of bits used to represent colour intensities of a pixel
-Next four bytes store the compression followed by the image size
-Next eight bytes store the X and Y resolution
-Final entries – number of colour map entries and the number of significant colours

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dword 4 Bitmap info header structure
size
Long 4 Bitmap width in pixels
Long 4 Bitmap height in pixels
Word 2 1
Word 2 Bits/pixel( 1 = monochrome )
Dword 4 Compression 0,8, 4
Dword 4 Image size in bytes
Long 4 Pixels/metre
Long 4 Pixels/metre
Dword 4 Number of colour indexes
Continued…….

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Colour Table & Image data
-Colour table is not present for bitmaps with 24 bit files.
-The format of the file depends on the number of bits used
to represent each pixel
-Bitmap data immediately following the colour table.
-Bitmap pixel data is stored upside down from its actual image
-A scan line must be zero padded to end
-The scan lines in the bitmap are stored from bottom to the top
-One important issue : managing junk bytes

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Usage of BMP format
-Simplicity
-Well documented and free of patents
-Most BMP files have a relatively large file size & can be compressed
with lossless data compression algorithm

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References
[1] https://en.Wikipedia.org/wiki/Image_file_formats
[2] John Miano, "Compressed Image File Formats“, ISBN - 0-201-60443-4,1999
[3] R. Witrow, “ OpenGL Graphics through Applications”, Springer-verlag London
Limited, 2008

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Forerunners in Technical Education
Thank you