codebook - Developer IT

Encryption: TCB (Tweaked CodeBook) algorithm - what is it?

- by FractalizeR

Can someone please provide a description of TCB algorithm?

Hello! Recently I wrote the algorithm to quantize an RGB image. Every pixel is represented by an (R,G,B) vector, and quantization codebook is a couple of 3-dimensional vectors. Every pixel of the image needs to be mapped to (say, "replaced by") the codebook pixel closest in terms of euclidean distance (more exactly, squared euclidean). I did it as follows: class EuclideanMetric(DistanceMetric): def __call__(self, x, y): d = x - y return sqrt(sum(d * d, -1)) class Quantizer(object): def __init__(self, codebook, distanceMetric = EuclideanMetric()): self._codebook = codebook self._distMetric = distanceMetric def quantize(self, imageArray): quantizedRaster = zeros(imageArray.shape) X = quantizedRaster.shape[0] Y = quantizedRaster.shape[1] for i in xrange(0, X): print i for j in xrange(0, Y): dist = self._distMetric(imageArray[i,j], self._codebook) code = argmin(dist) quantizedRaster[i,j] = self._codebook[code] return quantizedRaster ...and it works awfully, almost 800 seconds on my Pentium Core Duo 2.2 GHz, 4 Gigs of memory and an image of 2600*2700 pixels:( Is there a way to somewhat optimize this? Maybe the other algorithm or some Python-specific optimizations.

Read the article

Building ARM assembler vorbis decoder lib 'Tremolo' for iPhone

- by Joachim Bengtsson

I'm trying to compile Tremolo for iPhone. I've pulled in the files bitwise.c bitwiseARM.s codebook.c dpen.s dsp.c floor0.c floor1.c floor1ARM.s floor_lookup.c framing.c info.c mapping0.c mdct.c mdctARM.s misc.c res012.c into a new target, added the following custom settings: GCC_PREPROCESSOR_DEFINITIONS = _ARM_ASSEM_ GCC_C_LANGUAGE_STANDARD = gnu99 GCC_THUMB_SUPPORT = YES ... but as soon as xcode reaches the first assembler file, bitwiseARM.s, I get errors like these: /tremolo/bitwiseARM.s:3:Unknown pseudo-op: .global /tremolo/bitwiseARM.s:3:Rest of line ignored. 1st junk character valued 111 (o). /tremolo/bitwiseARM.s:4:Unknown pseudo-op: .global /tremolo/bitwiseARM.s:4:Rest of line ignored. 1st junk character valued 111 (o). /tremolo/bitwiseARM.s:5:Unknown pseudo-op: .global /tremolo/bitwiseARM.s:5:Rest of line ignored. 1st junk character valued 111 (o). /tremolo/bitwiseARM.s:6:Unknown pseudo-op: .global /tremolo/bitwiseARM.s:6:Rest of line ignored. 1st junk character valued 111 (o). /tremolo/bitwiseARM.s:11:bad instruction `STMFD r13!,{r10,r11,r14}' /tremolo/bitwiseARM.s:12:bad instruction `LDMIA r0,{r2,r3,r12}' /tremolo/bitwiseARM.s:16:bad instruction `SUBS r2,r2,r1' /tremolo/bitwiseARM.s:17:bad instruction `BLT look_slow' /tremolo/bitwiseARM.s:19:bad instruction `LDR r10,[r3]' The first error I could google, and changing .global to .globl fixed the first errors, but I still get the bad instructions, and I don't get why. Googling for the ARM instruction set, the above instructions look valid to me. I've tried toggling thumb support, and building for just armv7 instead of armv6, but neither helped.

Developer IT