Color Space
Table of Contents
Y'CbCr from RGB
YPbPr
def YPbPr(r, g, b, Kb=0.114, Kr=0.299): """Returns YPbPr (analog version of Y'CbCr) from R'G'B'. Y' = Kr * R' + (1 - Kr - Kb) * G' + Kb * B' Pb = 0.5 * (B' - Y') / (1 - Kb) Pr = 0.5 * (R' - Y') / (1 - Kr) R', G', B' in [0, 1] Y' in [0, 1] Pb in [-0.5, 0.5] Pr in [-0.5, 0.5] ref. http://en.wikipedia.org/wiki/YCbCr """ Y = Kr * r + (1 - Kr - Kb) * g + Kb * b Pb = 0.5 * (b - Y) / (1 - Kb) Pr = 0.5 * (r - Y) / (1 - Kr) return Y, Pb, Pr
CCIR601
def CCIR601(r, g, b): """Returns CCIR-YCbCr (601) from RGB. CCIR 601 defines the relationship between YCbCr and RGB values: Ey = 0.299R + 0.587G + 0.114B Ecb = 0.564(B - Ey) = -0.169R - 0.331G + 0.500B Ecr = 0.713(R - Ey) = 0.500R - 0.419G - 0.081B where Ey, R, G and B are in the range [0, 1] and Ecr and Ecb are in the range [-0.5, 0.5]. ref. http://www.fourcc.org/fccyvrgb.php """ y = 0.299*r + 0.587*g + 0.114*b cb = (b-y)*0.564 cr = (r-y)*0.713 return y, cb, cr def Rec601(r, g, b): """Returns Rec-YCbCr (601-1) from RGB. CCIR Rec. 601-1 spec used by TIFF & JPEG (from David): Y = 0.2989R + 0.5866G + 0.1145B R = Y + 0.0000Cb + 1.4022Cr Cb = -0.1687R - 0.3312G + 0.5000B G = Y - 0.3456Cb - 0.7145Cr Cr = 0.5000R - 0.4183G - 0.0816B B = Y + 1.7710Cb + 0.0000Cr where R, G, B in [0, 255]; Y in [0, 255]; and Cb, Cr in [-128, 127] """ y = 0.299*r + 0.587*g + 0.114*b cb = -0.1687*r - 0.3312*g + 0.5000*b cr = 0.5000*r - 0.4183*g - 0.0816*b return y, cb, cr
JFIF601
def JFIF601(r, g, b): """Returns JFIF-Y'CbCr (601) from "digital 8-bit R'G'B'" Y' = + 0.299 * R'd + 0.587 * G'd + 0.114 * B'd Cb = 128 - 0.168736 * R'd - 0.331264 * G'd + 0.5 * B'd Cr = 128 + 0.5 * R'd - 0.418688 * G'd - 0.081312 * B'd R'd, G'd, B'd in [0..255] Y', Cb, Cr in [0..255] ref. http://en.wikipedia.org/wiki/YCbCr Note PIL use this. """ y = 0.299 * r + 0.587 * g + 0.114 * b cb = 128 - 0.168736 * r - 0.331264 * g + 0.5 * b cr = 128 + 0.5 * r - 0.418688 * g - 0.081312 * b return y, cb, cr def PIL(r, g, b): """Returns PIL's JFIF-YCbCr (601) from 8-bit RGB. R, G, G in [0..255] Y, Cb, Cr in [0..255] """ from PIL import Image im = Image.fromstring('RGB', (1,1), chr(r)+chr(g)+chr(b)) return im.convert('YCbCr').getdata()[0]
Conversions
def Clip(y, cb, cr): clip = lambda x: int((x + 256) % 256) y, cb, cr = clip(y), clip(cb), clip(cr) return y, cb, cr def CCIR601FromJFIF601(y, cb, cr): return y, cb-128, cr-128
Usage Example
r, g, b = 0, 0, 255 print JFIF601(r, g, b) print PIL(r, g, b) print print CCIR601FromJFIF601(*JFIF601(r, g, b)) print CCIR601FromJFIF601(*PIL(r, g, b)) print YPbPr(r, g, b) print CCIR601(r, g, b) print Rec601(r, g, b) print print Clip(*CCIR601FromJFIF601(*JFIF601(r, g, b))) print Clip(*CCIR601FromJFIF601(*PIL(r, g, b))) print Clip(*YPbPr(r, g, b)) print Clip(*CCIR601(r, g, b)) print Clip(*Rec601(r, g, b))
Chroma Subsampling
Conversion between YUV422 and YUV444
def YUV444FromYUV422(YUV422): """Returns the YUV444 string from a given YUV422 string An input byte stream with the order: Y0 U0 Y1 V1 Y2 U2 Y3 V3 is reordered into: [Y0 U0 V1] [Y1 U0 V1] [Y2 U2 V3] [Y3 U2 V3] Example ------- >>> YUV444FromYUV422('00112233YUYVYUYV') '001101223323YUVYUVYUVYUV' See Also -------- http://en.wikipedia.org/wiki/Chroma_subsampling """ Y = YUV422[::2] U = "".join((u*2 for u in YUV422[1::4])) V = "".join((v*2 for v in YUV422[3::4])) return "".join(y+u+v for y, u, v in zip(Y,U,V)) def YUV422FromYUV444(YUV444): """Returns the YUV422 string from a given YUV444 string An input byte stream with the order: [Y0 U0 V0] [Y1 U1 V1] [Y2 U2 V2] [Y3 U3 V3] is reordered into: Y0 U0 Y1 V1 Y2 U2 Y3 V3 Example ------- >>> YUV422FromYUV444('000111222333YUVYUVYUVYUV') '00112233YUYVYUYV' See Also -------- http://en.wikipedia.org/wiki/Chroma_subsampling """ Y = YUV444[::3] U = YUV444[1::6] V = YUV444[5::6] UV = "".join((u+v for u, v in zip(U,V))) return "".join((y+uv for y, uv in zip(Y,UV)))
Conversion between YUV411 and YUV444
def YUV444FromYUV411(YUV411): """Returns the YUV444 string from a given YUV411 string An input byte stream with the order: Y0 U0 Y1 Y2 V2 Y3 is reordered into: [Y0 U0 V2] [Y1 U0 V2] [Y2 U0 V2] [Y3 U0 V2] Example ------- >>> YUV444FromYUV411('001223YUYYVY') '002102202302YUVYUVYUVYUV' See Also -------- http://en.wikipedia.org/wiki/Chroma_subsampling """ Y = "".join((y0+y1 for y0, y1 in zip(YUV411[::3], YUV411[2::3]))) U = "".join((u*4 for u in YUV411[1::6])) V = "".join((v*4 for v in YUV411[4::6])) return "".join((y+u+v for y, u, v in zip(Y,U,V))) def YUV411FromYUV444(YUV444): """Returns the YUV411 string from a given YUV444 string An input byte stream with the order: [Y0 U0 V0] [Y1 U1 V1] [Y2 U2 V2] [Y3 U3 V3] is reordered into: Y0 U0 Y1 Y2 V2 Y3 Example ------- >>> YUV411FromYUV444('000111222333YUVYUVYUVYUV') '001223YUYYVY' See Also -------- http://en.wikipedia.org/wiki/Chroma_subsampling """ Y0 = YUV444[::12] Y1 = YUV444[3::12] Y2 = YUV444[6::12] Y3 = YUV444[9::12] U0 = YUV444[1::12] V2 = YUV444[8::12] return "".join(("".join([y0,u0,y1,y2,v2,y3]) for y0,u0,y1,y2,v2,y3 in zip(Y0,U0,Y1,Y2,V2,Y3)))
Conversion between YUV420 and YUV444
def YUV444FromYUV420(YUV420, width): """Returns the YUV444 string from a given YUV420 string An input byte stream with the order: Yo0 Uo0 Yo1 Yo2 Uo2 Yo3 Ye0 Ve0 Ye1 Ye2 Ve2 Ye3 is reordered into: [Yo0 Uo0 Ve0] [Yo1 Uo0 Ve0] [Yo2 Uo2 Ve2] [Yo3 Uo2 Ve2] [Ye0 Uo0 Ve0] [Ye1 Uo0 Ve0] [Ye2 Uo2 Ve2] [Ye3 Uo2 Ve2] Example ------- >>> YUV444FromYUV420('001223001223ooooooeeeeeeYUYYUYYVYYVY', 4) '000100222322000100222322ooeooeooeooeeoeeoeeoeeoeYUVYUVYUVYUVYUVYUVYUVYUV' See Also -------- http://en.wikipedia.org/wiki/Chroma_subsampling """ from numpy import array, column_stack, hstack col = width*3/2 row = len(YUV420)/col YUV420 = array(tuple(YUV420)).reshape((row,col)) O420 = YUV420[0::2,:].flat E420 = YUV420[1::2,:].flat Yo = column_stack((O420[0::3], O420[2::3])).flat Ye = column_stack((E420[0::3], E420[2::3])).flat Uo0 = O420[1::6] Ve0 = E420[1::6] Uo2 = O420[4::6] Ve2 = E420[4::6] row /= 2 col *= 2 O444 = column_stack((Yo[0::4],Uo0,Ve0,Yo[1::4],Uo0,Ve0, Yo[2::4],Uo2,Ve2,Yo[3::4],Uo2,Ve2)).reshape((row,col)) E444 = column_stack((Ye[0::4],Uo0,Ve0,Ye[1::4],Uo0,Ve0, Ye[2::4],Uo2,Ve2,Ye[3::4],Uo2,Ve2)).reshape((row,col)) return "".join(hstack((O444, E444)).flat) def YUV420FromYUV444(YUV444, width): """Returns the YUV420 string from a given YUV444 string An input byte stream with the order: [Yo0 Uo0 Vo0] [Yo1 Uo1 Vo1] [Yo2 Uo2 Vo2] [Yo3 Uo3 Vo3] [Ye0 Ue0 Ve0] [Ye1 Ue1 Ve1] [Ye2 Ue2 Ve2] [Ye3 Ue3 Ve3] is reordered into: Yo0 Uo0 Yo1 Yo2 Uo2 Yo3 Ye0 Ve0 Ye1 Ye2 Ve2 Ye3 Example ------- >>> s = '000111222333000111222333ooooooooooooeeeeeeeeeeeeYUVYUVYUVYUVYUVYUVYUVYUV' >>> YUV420FromYUV444(s, 4) '001223001223ooooooeeeeeeYUYYUYYVYYVY' See Also -------- http://en.wikipedia.org/wiki/Chroma_subsampling """ from numpy import array, column_stack, hstack col = width*3 row = len(YUV444)/col YUV444 = array(tuple(YUV444)).reshape((row,col)) O444 = YUV444[0::2,:].flat E444 = YUV444[1::2,:].flat Yo0 = O444[0::12] Yo1 = O444[3::12] Yo2 = O444[6::12] Yo3 = O444[9::12] Uo0 = O444[1::12] Uo2 = O444[7::12] Ye0 = E444[0::12] Ye1 = E444[3::12] Ye2 = E444[6::12] Ye3 = E444[9::12] Ve0 = E444[2::12] Ve2 = E444[8::12] row /= 2 col /= 2 O420 = column_stack((Yo0,Uo0,Yo1,Yo2,Uo2,Yo3)).reshape((row,col)) E420 = column_stack((Ye0,Ve0,Ye1,Ye2,Ve2,Ye3)).reshape((row,col)) return "".join(hstack((O420, E420)).flat)
