BLP file A BLP file is a texture file format known to be used for games , including many Blizzard games such as " World of Warcraft " . The BLP file structure consists of a header including the palette , and up to 16 pre - rendered ' mipmaps ' . Texture sizes must be powers of two , though the two dimensions do not have to be equal ; 512x256 is valid , but 512x200 is not . The first mipmap ( ' mipmap ' level 0 ) is the full size image ; each subsequent mipmap halves both dimensions . The final ' mipmap ' should normally be 1x1 . Structure . BLP version 2 header . struct blp2header { Compression . BLP , DXT1 , DXT3 , DXT5 or Uncompressed 8 - bit per channel ARGB . BLP compression . This is the BLP specific image format , where the ' compression ' is via the use of a palette , and the use of alpha flags where ' alpha ' data is omitted if flags indicate that there is no alpha data at the end of the regular image data for a given ' mip ' level . If ' compression ' is 1 , each mipmap is stored as an array of 8 - bit values , one per pixel , left to right , top to bottom . Each value is an index to the palette . If ' alpha _ depth ' is > 0 , an alpha channel will immediately follow the image data , and comes in 1 , 4 , and 8 bit varieties . The 1 and 4 bit versions have multiple values packed into a single byte , with the least significant bit belonging to the first packed value . Uncompressed . If ' compression ' is 3 , each mipmap contains plain 32 - bit BGRA data . The ' alpha _ depth ' flag represents a set of bit flags rather than depth , as all images of this type seem to have 4 bytes per pixel regardless of depth , and it has been seen to exceed 8 . Their meaning is unknown . DXTC compression . DXT is an industry standard texture compression format , designed originally for efficiency in real time graphics rendering and decompression in hardware . Most current 3D hardware supports loading some form of DXTC data directly . See for more detail . If ' compression ' is 2 , each mipmap is composed of 4×4 blocks of pixels . The blocks and the pixels within each block are ordered from left to right , top to bottom . DXT1 . If ' alpha _ type ' is 0 , then DXT1 compression is used . Each block is 64 bits and begins with two 16 bit values , and are used to derived a 4 color palette . The values are interpreted as 565 RGB colors , with the least significant bits corresponding to blue , to create the first two colors in the palette . If the first value is less than or equal to the second , the final entry of the palette is reserved . If ' alpha _ depth ' is 0 , the reserved color is black . If ' alpha _ depth ' is 1 , the reserved color is transparent . The remaining colors are created by interpolating between the first two colors in the palette . The remaining 32 bits are 16 2 - bit values acting as a lookups to specify the colors in the block . DXT3 . If ' alpha _ type ' is 1 , then DXT3 compression is used . Each block is 128 bits and begins identically to DXT1 , except that no special color is reserved in the palette . It is followed by 16 4 - bit values corresponding to the alpha values for each of the pixels in the block . DXT5 . If ' alpha _ type ' is 7 , then DXT5 compression is used . This format was first used for Burning Crusade images . Each block is 128 bits and begins with two 8 - bit values to create an 8 element lookup table for alpha values . The first two elements in the lookup table are copies of those values . If the first value is less than or equal to the second , the final two entries of the lookup table are reserved for transparent and opaque . The remaining entries are created by interpolating between the first two entries in the lookup table . The next 48 bits make up 16 3 - bit values acting as lookups specifying the alpha values for each of the pixels in the block . The remaining 64 bits are identical to DXT1 , except that no special color is reserved in the palette . Sample Files . Below is a list of BLP files , each with some unique characteristic . The following files require an MPQ viewer to access , as they aren ' t exposed by Blizzard ' s AddOn Kit . Conversion tools . There exist BLP tools to convert both from and to the BLP format . They can be found in UI Authors resource list .