Enhanced Motion Estimation via Edge Detection Using PLX Sub-Word Parallel ISA

Acceleration of motion estimation by edge detection algorithm using PLX sub-word parallel ISA Dongkeun Oh Sanghamitra Roy

Low bit rate Video coding(1) • Block based algorithms • H.263, MPEG-1,2 • Good • easy to implement, good image quality at low bit rates • Bad • Image quality degraded at very low bit rates

Low bit rate video coding (2) • Object or Segmentation based algorithm • Subdividing an image into moving objects and background • Good : Efficient compression rate • Bad : Hard to implement • Necessary condition • Accurate representation of the shape of Objects

Edge detection for object recognition • Block is visually continuous and discontinuous • Lines of discontinuous interface: edge • Coded edges : structure of an image • Edge detection • Sobel • Laplace • Canny’s

Canny’s Edge detection • Stages • 1. Gaussian Smoothing • 2. First derivative for x,y of all pixels • 3. Magnitude of the gradient • 4. Non-maximal suppression • 5. Use hysteresis to mark the edge pixels • We simulate 2nd stages using PLX code

Derivative Mask Gx(z5)=(z6-z4) Gy(z5)=(z8-z2 )

Unfold C code for x-derivative calculation for(r=0; r < rows; r++) { pos = r * cols; del_x[pos] = s[pos + 1] – s[pos]; for(c = 1; c < (cols – 1); c++, pos++) { del_x[pos] = s[pos + 1] – s[pos – 1]; } del_x[pos] = s[pos] – s[pos – 1]; }

Loop unfolded C code for sub-word parallel implementation for(r=0; r < 100; r++) { pos = r * cols; del_x[pos] = s[pos + 1] – s[pos]; for(c = 1; c < 24; c++, pos+= 4) { del_x[pos] = s[pos + 1] – s[pos – 1]; del_x[pos + 1] = s[pos + 2] – s[pos]; del_x[pos + 2] = s[pos + 3] – s[pos + 1]; del_x[pos + 3] = s[pos + 4] – s[pos + 2]; } …. del_x[pos] = s[pos] – s[pos – 1]; }

PLX sub-word parallel ISA • Sub-word parallel ISA • 1, 2, 4, or 8 bytes sub-words • 32 general purpose registers • Aligned memory address • 4/8 bytes • SIMD instructions allow parallel operations with faster performance

Issues in PLX implementation • Interfacing with C code • short int = 2 bytes • use fwrite/fread to write/read binary data from C • Memory aligned load • load address: multiple of 4 bytes to avoid trap • Load from aligned address and shift/add to get required sub-words • Loops • using predicated jump instruction

Results PLX FFCF, FFB5, FFB5, 0002 C

Snapshot of PLX code

Thanks !

Enhanced Motion Estimation via Edge Detection Using PLX Sub-Word Parallel ISA