IBM UltiMotion

This page is based on the document 'Description of the IBM UltiMotion (ULTI) Video Codec' by Mike Melanson and Konstantin Shishkov found at http://multimedia.cx/ultimotion-format.txt.

• FourCC: ULTI
• Company: IBM
• Official Description: http://multimedia.cx/UMSPEC.ZIP
• Samples: http://www.mplayerhq.hu/MPlayer/samples/V-codecs/ULTI/

IBM UltiMotion (henceforth ULTI) is a video codec typically seen in AVI files, though there is no reason it could not be used in other container formats.

Decoding Algorithm

The ULTI algorithm operates natively on a scaled-down YUV 4:1:0 planar colorspace. This means that for each 4x4 block of pixels, each of the 16 pixels has a luminance (Y) sample and the entire block shares one blue chrominance sample (C_b or U) and one red chrominance sample (C_r or V). The colorspace is actually non-linear quantized to fixed values from 2 tables. Indices into these tables (64 possible values for luminance and 16 for chrominance) are transmitted in the final bitstream.

The ULTI algorithm codes a frame by dividing it into a series of 8x8 blocks. Each 8x8 block is subdivided and coded as 4 4x4 blocks. The 4 sub blocks, 0-3, are coded in the following arrangement:

 0 3
 1 2

Each block can be coded using the same chrominance samples, or each sub block can be coded with its own pair of chrominance samples. Each sub block has 16 luminance samples that can be coded using a variety of methods.

To decode a frame of UltiMotion data, follow this process:

initialize uniq and mode flags to 0, initialize modifier to 0

for each 8x8 block in the frame, iterating from left -> right, top -> bottom:

 get the next byte in the stream (b0)
 if (b0 & 0xF8) == 0x70, handle escape code:
   if b0 is 0x70
     modifier = next byte in stream
     note: only modifier values of 0 or 1 are valid
   if b0 is 0x71
     set uniq flag
   if b0 is 0x72
     toggle mode flag
   if b0 is 0x73
     end of frame, stop decoding
   if b0 is 0x74
     get the next byte in stream (b1)
     skip next (b1) blocks in the output frame (unchanged from previous 
       frame)

 else
   chrominance byte = 0
   if either the mode or uniq flags are set
     color flag = 1, each sub block has a different chrominance byte
     uniq = 0
   else
     color flag = 0, all 4 sub blocks use the same chrominance byte
     if b0 is non-zero
       chrominance byte = next byte from stream

   for each 4x4 sub block in the block, arranged in the sub block pattern:

     extract sub block coding mode from b0:
       bits 7-6: sub block 0 coding mode
       bits 5-4: sub block 1 coding mode
       bits 3-2: sub block 2 coding mode
       bits 1-0: sub block 3 coding mode

     if coding mode is non-zero and color flag is 1
       chrominance byte = next byte from stream

     coding mode 0:
       skip sub block (unchanged from the previous frame)

     coding mode 1:
       paint the luminance samples using a gradient pattern based on one 
         6-bit sample coded in the stream

       get next byte from stream (b0)
       bits 7-6 of b0 indicate gradient fill pattern:
         0 = gradient fill pattern 0
         1 = gradient fill pattern 2
         2 = gradient fill pattern 6
         3 = gradient fill pattern 4, swap Y0 with Y3 and Y1 with Y2 
             after unpacking Y samples
       bits 5-0 of b1 indicate luminance sample Y0
       Y1 = Y0
       if gradient fill pattern is pattern 0
         Y2 = Y0 + 1 (saturated to an upper limit of 0x3F)
         Y3 = Y2
       else
         Y2 = Y3 = Y0
       fill luminance samples according to Y0..Y3 and the gradient fill 
         pattern (see section Gradient Fill Patterns)

     coding mode 2:
       paint the luminance samples using a gradient pattern based on 
         either 4 6-bit samples coded in the stream or 4 6-bit samples 
         retrieved from a 16,384-entry codebook using an index coded in 
         the stream
       if modifier is non-zero
         get the next 3 bytes from the stream as a big endian 24-bit 
           number:
         Y0 = bits 23-18
         Y1 = bits 17-12
         Y2 = bits 11-6
         Y3 = bits 5-0
         fill luminance samples according to Y0..Y3 and gradient fill 
           pattern 8 (see section Gradient Fill Patterns)

       else (modifier is 0)
         get the next 2 bytes from the stream as a big endian 16-bit 
           number:
         gradient fill pattern = bits 15-12
         luminance codebook index = bits 11-0
         Y0..Y3 are set according to the codebook entry (see References 
           for UltiMotion luminance codebook)
         if bit 3 of the gradient fill pattern is set, swap Y0 with Y3 
           and Y1 with Y2; clear bit 3 of the gradient fill pattern
         fill luminance samples according to Y0..Y3 and the gradient fill 
           pattern (see section Gradient Fill Patterns)

     coding mode 3:
       flexible coding mode that can paint the luminance samples with 16 
         6-bit samples coded in the stream, or with a gradient fill 
         pattern and 4 6-bit luminance samples coded in the stream, or 
         with an arbitrary pattern using 2 luminance samples and a set of 
         flags coded in the stream
       if modifier is non-zero
         get the next 16 6-bit numbers from the stream as the 16 
           luminance samples for the sub block, thus consuming 96 bits, 
           or 12 bytes from the stream
       if modifier is 0
         get the next byte in the stream (b0)
         if bit 7 of b0 is set
           gradient fill pattern = bits 6-4 of b0
           get the next byte in the stream (b1)
           Y0 = ((b0 & 0x0F) << 2) | (b1 >> 6)
           Y1 = bits 5-0 of b1
           Y2 = next byte in stream & 0x3F
           Y3 = next byte in stream & 0x3F
           fill luminance samples according to Y0..Y3 and the gradient 
             fill pattern (see section Gradient Fill Patterns)
         else
           flagsA = b0
           flagsB = next byte in the stream
           Y0 = next byte in stream & 0x3F
           Y1 = next byte in stream & 0x3F
           the 16 bits between flagsA and flagsB represent the pattern 
             used to place either Y0 or Y1 into the luminance grid

             A7 A6 A5 A4
             A3 A2 A1 A0
             B7 B6 B5 B4
             B3 B2 B1 B0

             for example, if bit 3 of flagsB is 1, Y1 would be used in 
             the lower left corner of the sub block, else Y0

     finally, output sub block:
       bits 7-4 of the chrominance byte represent the red chrominance 
         value for the sub block while bits 3-0 represent the blue value
       convert the 16 luminance values and the 2 chrominance values to a 
         proper YUV colorspace using the conversion tables in Appendix A

Gradient Fill Patterns

The ULTI codec has 9 gradient fill patterns for painting 4x4 sub blocks of luminance data using 4 luminance samples.

• Gradient Pattern 0:

 0 1 2 3
 0 1 2 3
 0 1 2 3
 0 1 2 3

• Gradient Pattern 1:

 1 2 3 3
 0 1 2 3
 0 1 2 3
 0 0 1 2

• Gradient Pattern 2:

 1 2 3 3
 1 2 2 3
 0 1 1 2
 0 0 1 2

• Gradient Pattern 3:

 2 3 3 3
 1 2 2 3
 0 1 1 2
 0 0 0 1

• Gradient Pattern 4:

 3 3 3 3
 2 2 2 2
 1 1 1 1
 0 0 0 0

• Gradient Pattern 5:

 3 3 3 2
 3 2 2 1
 2 1 1 0
 1 0 0 0

• Gradient Pattern 6:

 3 3 2 2
 3 2 1 1
 2 2 1 0
 1 1 0 0

• Gradient Pattern 7:

 3 3 2 1
 3 2 1 0
 3 2 1 0
 2 1 0 0

• Gradient Pattern 8:

 0 0 1 1
 0 0 1 1
 2 2 3 3
 2 2 3 3

Converting UltiMotion Scaled YUV To Correct YUV

To convert UltiMotion 6-bit luminance values to proper luminance samples, use the following conversion table:

unsigned char ulti_lumas[64] =
   { 0x10, 0x13, 0x17, 0x1A, 0x1E, 0x21, 0x25, 0x28,
     0x2C, 0x2F, 0x33, 0x36, 0x3A, 0x3D, 0x41, 0x44,
     0x48, 0x4B, 0x4F, 0x52, 0x56, 0x59, 0x5C, 0x60,
     0x63, 0x67, 0x6A, 0x6E, 0x71, 0x75, 0x78, 0x7C,
     0x7F, 0x83, 0x86, 0x8A, 0x8D, 0x91, 0x94, 0x98,
     0x9B, 0x9F, 0xA2, 0xA5, 0xA9, 0xAC, 0xB0, 0xB3,
     0xB7, 0xBA, 0xBE, 0xC1, 0xC5, 0xC8, 0xCC, 0xCF,
     0xD3, 0xD6, 0xDA, 0xDD, 0xE1, 0xE4, 0xE8, 0xEB};
     

To convert UltiMotion 4-bit chrominance values to proper chrominance samples, use the following conversion table:

unsigned char ulti_chromas[16] =
   { 0x60, 0x67, 0x6D, 0x73, 0x7A, 0x80, 0x86, 0x8D,
     0x93, 0x99, 0xA0, 0xA6, 0xAC, 0xB3, 0xB9, 0xC0};

References

• XAnim

• UltiMotion Luminance Codebook