Example of converting yv12 to rgb24 using the lookup table method (with code)

Recently, many users frequently asked questions about YUV-to-RGB conversion. Here I will give a unified answer and sample code for your reference (using yv12-to-rgb24 as an example ).

Yv12 bytes are arranged as follows:

<-Width->
Yyyy... Yyyy ^
Y |
.. Height
... |
Yyyy... Yyyy v
<-Width/2->
VV... VV ^
... |
VV... VV height
UU... UU |
... |
UU... UU v

The format of rgb24 bytes is as follows:
<-Width * 3->
Bgrbgr... Bgrbgr ^
... |
.. Height
... |
Bgrbgr... Bgrbgr v

For details about pixel layout and word throttling, refer to the Microsoft website.
The conversion formula is in the following format:
R = Y + 1.402 (Cr-128)
G = Y-0.34414 (CB-128)-0.71414 (Cr-128)
B = Y + 1.772 (CB-128)
There are a large number of floating-point operations in this formula, seriously affecting the speed. here we need to optimize the floating-point operation to convert it into an integer operation. The formula optimization is as follows:
Rdif = V + (V * 103)> 8 );
Invgdif = (u * 88)> 8) + (V * 183)> 8 );
Bdif = u + (u * 198)> 8 );

R = yuvdata [ypos] + rdif;
G = yuvdata [ypos]-invgdif;
B = yuvdata [ypos] + bdif;

The formula above has improved much speed than the floating point operation, but we can find that we can continue to optimize it.
All values of y u v are 0 ~ Between 255, so the rdif invgdif bdif values are in a certain range. We can calculate these values in advance and put them in the memory. during conversion, we can directly look up the table to get them, this saves a lot of integer addition, multiplication, and shift operations. The rdif invgdif bdif value is calculated based on the r g B formula. Of course, here we can also calculate the RGB value through the secondary lookup table. Here we use a lookup method as an example to describe the conversion from yv12 to rgb24. The speed should be above FPS. For the second lookup method, please implement it by yourself.

Const int table_fv1 [256] = {-180,-179,-177,-176,-174,-173,-172,-170,-169,-167, -166,-165,-163,-162,-160,-159,-158,-156,-155,-153,-152,-151,-149, -148,-146,-145,-144,-142,-141,-139,-138,-137,-135,-134,-132,-131, -130,-128,-127,-125,-124,-123,-121,-120,-118,-117,-115,-114,-113, -111,-110,-108,-107,-106,-104,-103,-101,-100,-99,-97,-96,-94, -93,-92,-90,-89,-87,-86,-85,-83,-82,-80,-79,-78,-76, -75,-73,-72,-71,-69,-68,-66,-65,-64,-62,-61,-59,-58, -57,-55,-54,-52,-51,-50,-48,-47,-45,-44,-43,-41,-40, -38,-37,-36,-34,-33,-31,-30,-29,-27,-26,-24,-23,-22, -20,-19,-17,-16,-15,-13,-12,-10,-9,-8,-6,-5,-3, -2, 0, 1, 2, 4, 5, 7, 8, 9, 11, 12, 14, 15, 16, 18, 19, 21, 22, 23, 25, 26, 28, 29, 30, 32, 33, 35, 36, 37, 39, 40, 42, 43, 44, 46, 47, 49, 50, 51, 53, 54, 56, 57, 58, 60, 61, 63, 64, 65, 67, 68, 70, 71, 72, 74, 75, 77, 78, 79, 81, 82, 84, 85, 86, 88, 89, 91, 92, 93, 95, 96, 98, 99,100,102,103,105,106,107,109,110,112,113,114,116,117,119,120,122,123,124,126,127,129,130,131,133,134,136,137,138,140,141,143,144,145,147,148,150,151,152,154,155,157,158,159,161,162,164,165,166,168,169,171,172,173,175,176,178 };
Const int table_fv2 [256] = {-92,-91,-91,-90,-89,-88,-88,-87,-86,-86, -85,-84,-83,-83,-82,-81,-81,-80,-79,-78,-78,-77,-76, -76,-75,-74,-73,-73,-72,-71,-71,-70,-69,-68,-68,-67, -66,-66,-65,-64,-63,-63,-62,-61,-61,-60,-59,-58,-58, -57,-56,-56,-55,-54,-53,-53,-52,-51,-51,-50,-49,-48, -48,-47,-46,-46,-45,-44,-43,-43,-42,-41,-41,-40,-39, -38,-38,-37,-36,-36,-35,-34,-33,-33,-32,-31,-31,-30, -29,-28,-28,-27,-26,-26,-25,-24,-23,-23,-22,-21,-21, -20,-19,-18,-18,-17,-16,-16,-15,-14,-13,-13,-12,-11, -11,-10,-9,-8,-8,-7,-6,-6,-5,-4,-3,-3,-2, -1, 0, 0, 1, 2, 2, 3, 4, 5, 5, 6, 7, 7, 8, 9, 10, 10, 11, 12, 12, 13, 14, 15, 15, 16, 17, 17, 18, 19, 20, 20, 21, 22, 22, 23, 24, 25, 25, 26, 27, 27, 28, 29, 30, 30, 31, 32, 32, 33, 34, 35, 35, 36, 37, 37, 38, 39, 40, 40, 41, 42, 42, 43, 44, 45, 45, 46, 47, 47, 48, 49, 50, 50, 51, 52, 53, 54, 55, 55, 56, 57, 57, 58, 59, 60, 60, 61, 62, 62, 63, 64, 65, 65, 66, 67, 68, 69, 70, 70, 71, 72, 72, 73, 74, 75, 75, 76, 77, 77, 78, 79, 80, 80, 81, 82, 82, 83, 84, 85, 85, 86, 87, 87, 88, 89, 90, 90 };
Const int table_fu1 [256] = {-44,-44,-44,-43,-43,-43,-42,-42,-42,-41, -41,-41,-40,-40,-40,-39,-39,-39,-38,-38,-38,-37,-37, -37,-36,-36,-36,-35,-35,-35,-34,-34,-33,-33,-33,-32, -32,-32,-31,-31,-31,-30,-30,-30,-29,-29,-29,-28,-28, -28,-27,-27,-27,-26,-26,-26,-25,-25,-25,-24,-24,-24, -23,-23,-22,-22,-22,-21,-21,-21,-20,-20,-20,-19,-19, -19,-18,-18,-18,-17,-17,-17,-16,-16,-16,-15,-15,-15, -14,-14,-14,-13,-13,-13,-12,-12,-11,-11,-11,-10,-10, -10,-9,-9,-9,-8,-8,-8,-7,-7,-7,-6,-6,-6, -5,-5,-5,-4,-4,-4,-3,-3,-3,-2,-2,-2,-1, -1, 0, 0, 0, 1, 1, 1, 2, 2, 2, 3, 3, 4, 4, 4, 5, 5, 5, 6, 6, 6, 7, 7, 7, 8, 8, 8, 9, 9, 9, 10, 10, 11, 11, 12, 12, 12, 13, 13, 13, 14, 14, 14, 15, 15, 15, 16, 16, 16, 17, 17, 17, 18, 18, 19, 19, 19, 20, 20, 20, 21, 21, 22, 22, 22, 23, 23, 23, 24, 24, 25, 25, 25, 26, 26, 26, 27, 27, 27, 28, 28, 28, 29, 29, 29, 30, 30, 30, 31, 31, 31, 32, 32, 33, 33, 33, 34, 34, 34, 35, 35, 35, 36, 36, 36, 37, 37, 37, 38, 38, 38, 39, 39, 40, 40, 40, 41, 41, 41, 42, 42, 42, 43, 43 };
Const int table_fu2 [256] = {-227,-226,-224,-222,-220,-219,-217,-215,-213,-212, -210,-208,-206,-204,-203,-201,-199,-197,-196,-194,-192,-190,-188, -187,-185,-183,-181,-180,-178,-176,-174,-173,-171,-169,-167,-165, -164,-162,-160,-158,-157,-155,-153,-151,-149,-148,-146,-144,-142, -141,-139,-137,-135,-134,-132,-130,-128,-126,-125,-123,-121,-119, -118,-116,-114,-112,-110,-109,-107,-105,-103,-102,-100,-98,-96, -94,-93,-91,-89,-87,-86,-84,-82,-80,-79,-77,-75,-73, -71,-70,-68,-66,-64,-63,-61,-59,-57,-55,-54,-52,-50, -48,-47,-45,-43,-41,-40,-38,-36,-34,-32,-31,-29,-27, -25,-24,-22,-20,-18,-16,-15,-13,-11,-9,-8,-6,-4, -2, 0, 1, 3, 5, 7, 8, 10, 12, 14, 15, 17, 19, 21, 23, 24, 26, 28, 30, 31, 33, 35, 37, 39, 40, 42, 44, 46, 47, 49, 51, 53, 54, 56, 58, 60, 62, 63, 65, 67, 69, 70, 72, 74, 76, 78, 79, 81, 83, 85, 86, 88, 90, 92, 93, 95, 97, 99,101,102,104,106,108,109,111,113,115,117,118,120,122,124,125,127,129,131,133,134,136,138,140,141,143,145,147,148,150,152,154,156,157,159,161,163,164,166,168,170,172,173,175,177,179,180,182,184,186,187,189,191,193,195,196,198,200,202,203,205,207,209,211,212,214,216,218,219,221,223,225 };

# Define width 320
# Define height 240
# Define pixelsize width * Height

Bool yv12_to_rgb24 (unsigned char * pyv12, unsigned char * prgb24)
{
If (! Pyv12 |! Prgb24)
Return false;
 
Const long nylen = long (pixelsize );
Const int nhfwidth = (width> 1 );
 
If (nylen <1 | nhfwidth <1)
Return false;
 
// Y Data
Unsigned char * ydata = pyv12;
// V Data
Unsigned char * vdata = & ydata [nylen];
// U data
Unsigned char * udata = & vdata [nylen> 2];
 
If (! Udata |! Vdata)
Return false;
 
Int RGB [3];
Int I, j, m, n, x, y, Pu, PV, Py, rdif, invgdif, bdif;
M =-width;
N =-nhfwidth;

Bool addhalf = true;
For (y = 0; y M + = width;
If (addhalf ){
N + = nhfwidth;
Addhalf = false;
} Else {
Addhalf = true;
}
For (x = 0; x <width; X ++ ){
I = m + X;
J = N + (x> 1 );

Py = ydata [I];

// Search tables to get rdif invgdif and bidif
Rdif = table_fv1 [vdata [J]; // fv1
Invgdif = table_fu1 [udata [J] + table_fv2 [vdata [J]; // FU1 + fv2
Bdif = table_fu2 [udata [J]; // FU2

 

// Change it

// ==================================

// RGB [2] = py + rdif; // R
// RGB [1] = Py-invgdif; // G
// RGB [0] = py + bdif; // B
// ==================================

RGB [0] = py + rdif; // R
RGB [1] = Py-invgdif; // G
RGB [2] = py + bdif; // B
J = nylen-width-M + X;
I = (j <1) + J;

// Copy this pixel to RGB data
For (j = 0; j <3; j ++)
{
If (RGB [J]> = 0 & RGB [J] <= 255 ){
Prgb24 [I + J] = RGB [J];
}
Else {
Prgb24 [I + J] = (RGB [J] <0 )? 0: 255;
}
}
}
}
Return true;
}