# IBM UltiMotion

- FourCC: ULTI
- Company: IBM
- Official Description: Ultimotion Digital Video Data Stream Specification
- Additional Documentation: 'Description of the IBM UltiMotion (ULTI) Video Codec' by Mike Melanson and Konstantin Shishkov .
- Samples: http://samples.mplayerhq.hu/V-codecs/ULTI/
- Codec: Win32 Ultimotion decoder

IBM Ultimotion is a video codec typically seen in AVI files, though there is no reason it could not be used in other container formats. Full codecs were available for Windows 3.1 (VfW), OS/2 and AIX. It is primarily a vector quantizing algorithm with simple inter-frame coding (unchanged block). Ultimotion encoding is significantly more computationally intensive than decoding.

## Decoding Algorithm

The Ultimotion algorithm operates natively on a scaled-down YUV 4:1:0 planar colorspace. This means that for each 4x4 block of pixels (quadrant), each of the 16 pixels has a luminance (Y) sample and the entire block shares one chrominance sample expressed as two color difference components : C_{b} (or U) and 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 each chrominance component) are transmitted in the final bitstream.

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

0 3 1 2

Each block can be encoded using a single chrominance sample or unique chrominance sample for each quadrant. Each quadrant 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 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 mode = next byte in stream note: only mode values of 0 or 1 are valid if b0 is 0x71 uniq flag = -1 if b0 is 0x72 toggle uniq flag (0/1) 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 if b0 is non-zero and uniq flag is 0 chrominance byte = next byte from stream for each 4x4 quadrant in the block, arranged in the quadrant pattern: extract quadrant coding mode from b0: bits 7-6: quadrant 0 coding mode bits 5-4: quadrant 1 coding mode bits 3-2: quadrant 2 coding mode bits 1-0: quadrant 3 coding mode if coding mode is non-zero and uniq flag is non-zero chrominance byte = next byte from stream coding mode 0: skip quadrant (unchanged from the previous frame) coding mode 1: paint the luminance samples using a gradient pattern based on one sample coded in the stream get next byte from stream (b1) bits 7-6 of b1 indicate gradient fill pattern: 0 = gradient fill pattern A 1 = gradient fill pattern 2 2 = gradient fill pattern 6 3 = gradient fill pattern B bits 5-0 of b1 indicate luminance sample Y0 Y1 = Y0, Y2 = Y0 + 1, Y3 = Y0 + 1 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 four samples retrieved from a 4,096-entry codebook using an index coded in the stream or four samples coded in the stream if mode 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 section Luminance Codebook Enumeration) 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) else (mode 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 C (see section Gradient Fill Patterns) coding mode 3: flexible coding mode that can paint the luminance samples with an arbitrary pattern using two samples and a set of flags coded in the stream, or with a gradient fill pattern and four samples coded in the stream, or with 16 samples coded in the stream if mode is 0 if bit 7 of b1 is 0 flagsA = b1 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 quadrant, else Y0 else gradient fill pattern = bits 6-4 of b1 get the next byte in the stream (b2) Y0 = ((b1 & 0x0F) << 2) | (b2 >> 6) Y1 = bits 5-0 of b2 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 (mode is non-zero) get the next 12 bytes from the stream as 16 6-bit numbers as the 16 luminance samples (Y0..Y15) for the quadrant fill luminance samples according to Y0..Y15 and gradient fill pattern D (see section Gradient Fill Patterns) finally, output quadrant: bits 7-4 of the chrominance byte represent the Cr (or V) component while bits 3-0 represent the Cb (U) component convert the 16 luminance values and the 2 chrominance values to a proper YUV colorspace using the conversion tables in Appendix A if uniq flag is -1 uniq flag = 0

## Gradient Fill Patterns

The ULTI codec has 12 gradient fill patterns for painting 4x4 sub blocks of luminance data using 4 (or 16) luminance samples.

- Gradient Pattern 0: (0 degrees)

Y0 Y1 Y2 Y3 Y0 Y1 Y2 Y3 Y0 Y1 Y2 Y3 Y0 Y1 Y2 Y3

- Gradient Pattern 1: (22.5 degrees)

Y1 Y2 Y3 Y3 Y0 Y1 Y2 Y3 Y0 Y1 Y2 Y3 Y0 Y0 Y1 Y2

- Gradient Pattern 2: (45 degrees)

Y1 Y2 Y3 Y3 Y1 Y2 Y2 Y3 Y0 Y1 Y1 Y2 Y0 Y0 Y1 Y2

- Gradient Pattern 3: (67.5 degrees)

Y2 Y3 Y3 Y3 Y1 Y2 Y2 Y3 Y0 Y1 Y1 Y2 Y0 Y0 Y0 Y1

- Gradient Pattern 4: (90 degrees)

Y3 Y3 Y3 Y3 Y2 Y2 Y2 Y2 Y1 Y1 Y1 Y1 Y0 Y0 Y0 Y0

- Gradient Pattern 5: (112.5 degrees)

Y3 Y3 Y3 Y2 Y3 Y2 Y2 Y1 Y2 Y1 Y1 Y0 Y1 Y0 Y0 Y0

- Gradient Pattern 6: (135 degrees)

Y3 Y3 Y2 Y2 Y3 Y2 Y1 Y1 Y2 Y2 Y1 Y0 Y1 Y1 Y0 Y0

- Gradient Pattern 7: (157.5 degrees)

Y3 Y3 Y2 Y1 Y3 Y2 Y1 Y0 Y3 Y2 Y1 Y0 Y2 Y1 Y0 Y0

- Gradient Pattern A: (homogeneous)

Y0 Y0 Y0 Y0 Y0 Y0 Y0 Y0 Y0 Y0 Y0 Y0 Y0 Y0 Y0 Y0

- Gradient Pattern B: (270 degrees)

Y0 Y0 Y0 Y0 Y1 Y1 Y1 Y1 Y2 Y2 Y2 Y2 Y3 Y3 Y3 Y3

- Gradient Pattern C: (subsampled)

Y0 Y0 Y1 Y1 Y0 Y0 Y1 Y1 Y2 Y2 Y3 Y3 Y2 Y2 Y3 Y3

- Gradient Pattern D: (16 samples)

Y0 Y1 Y2 Y3 Y4 Y5 Y6 Y7 Y8 Y9 Y10 Y11 Y12 Y13 Y14 Y15

## Luminance Codebook Enumeration

The following pseudo-code creates the Ultimotion Luminance Transition Coding codebook

i = 0 for Y0 = 0 to 61 for Y3 = Y0 + 2 to 63 Yd = Y3 - Y0 if Yd in (2,3,5,6,7,8,11,14,17,20) LTC[i++] = (Y0, Y0 + Yd/3, Y3 - Yd/3, Y3) endif if Yd in (4,5,6,7,8,11,14,17,20,23,26,29,32,36) LTC[i++] = (Y0, Y0 + Yd/2, Y3 - Yd/4, Y3) LTC[i++] = (Y0, Y0 + Yd/4, Y3 - Yd/4, Y3) LTC[i++] = (Y0, Y0 + Yd/4, Y3 - Yd/2, Y3) endif if Yd in (6,8,11,14,17,20,23,26,29,32,35,40,46) LTC[i++] = (Y0, Y3, Y3, Y3) LTC[i++] = (Y0, Y0, Y3, Y3) LTC[i++] = (Y0, Y0, Y0, Y3) endif next Y3 next Y0

It should be noted there is an error in the "Ultimotion Digital Video Data Stream Specification" - the pre-determined linear transitions are for Y deltas of 2, 3, 5, 6, 7, 8, 11, 14, 17, 20 (not 4). (If 4 is included then there are 4156 transitions. The various transitions are handled by the low contrast edge transitions.)

## 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};