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magic constants explained

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This commit is contained in:
Rostislav Vasilikhin 2017-07-06 00:23:58 +03:00
parent 704c688225
commit aa621d6f3c
2 changed files with 8 additions and 0 deletions
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4
modules/imgproc/src/color.cpp
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@ -7011,6 +7011,8 @@ struct RGB2Luv_b
const float* _whitept, bool _srgb ) const float* _whitept, bool _srgb )
: srccn(_srccn), cvt(3, blueIdx, _coeffs, _whitept, _srgb) : srccn(_srccn), cvt(3, blueIdx, _coeffs, _whitept, _srgb)
{ {
//0.72033 = 255/(220+134), 96.525 = 134*255/(220+134)
//0.9732 = 255/(140+122), 136.259 = 140*255/(140+122)
#if CV_NEON #if CV_NEON
v_scale_inv = vdupq_n_f32(1.f/255.f); v_scale_inv = vdupq_n_f32(1.f/255.f);
v_scale = vdupq_n_f32(2.55f); v_scale = vdupq_n_f32(2.55f);
@ -7211,6 +7213,8 @@ struct Luv2RGB_b
const float* _whitept, bool _srgb ) const float* _whitept, bool _srgb )
: dstcn(_dstcn), cvt(3, blueIdx, _coeffs, _whitept, _srgb ) : dstcn(_dstcn), cvt(3, blueIdx, _coeffs, _whitept, _srgb )
{ {
// 1.388235294117647 = (220+134)/255
// 1.027450980392157 = (140+122)/255
#if CV_NEON #if CV_NEON
v_scale_inv = vdupq_n_f32(100.f/255.f); v_scale_inv = vdupq_n_f32(100.f/255.f);
v_coeff1 = vdupq_n_f32(1.388235294117647f); v_coeff1 = vdupq_n_f32(1.388235294117647f);

4
modules/imgproc/src/opencl/cvtcolor.cl
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@ -2035,7 +2035,9 @@ __kernel void BGR2Luv(__global const uchar * src, int src_step, int src_offset,
float v = L*fma(2.25f, Y*d, -_vn); float v = L*fma(2.25f, Y*d, -_vn);
dst[0] = SAT_CAST(L * 2.55f); dst[0] = SAT_CAST(L * 2.55f);
//0.72033 = 255/(220+134), 96.525 = 134*255/(220+134)
dst[1] = SAT_CAST(fma(u, 0.72033898305084743f, 96.525423728813564f)); dst[1] = SAT_CAST(fma(u, 0.72033898305084743f, 96.525423728813564f));
//0.9732 = 255/(140+122), 136.259 = 140*255/(140+122)
dst[2] = SAT_CAST(fma(v, 0.9732824427480916f, 136.259541984732824f)); dst[2] = SAT_CAST(fma(v, 0.9732824427480916f, 136.259541984732824f));
++y; ++y;
@ -2137,7 +2139,9 @@ __kernel void Luv2BGR(__global const uchar * src, int src_step, int src_offset,
{ {
float d, X, Y, Z; float d, X, Y, Z;
float L = src[0]*(100.f/255.f); float L = src[0]*(100.f/255.f);
// 1.388235294117647 = (220+134)/255
float u = fma(convert_float(src[1]), 1.388235294117647f, -134.f); float u = fma(convert_float(src[1]), 1.388235294117647f, -134.f);
// 1.027450980392157 = (140+122)/255
float v = fma(convert_float(src[2]), 1.027450980392157f, - 140.f); float v = fma(convert_float(src[2]), 1.027450980392157f, - 140.f);
if(L >= 8) if(L >= 8)
{ {