Convert Yuv420 to rgb and show on qt pixmap - c++

Question

I want to convert a yuv picture into RGB to display on a QT pixmap. What I have right now is that I see a empty pixmap.
int convertYUVtoRGB(int y, int u, int v) {
int r,g,b;
r = y + (int)(1.402f*v);
g = y - (int)(0.344f*u +0.714f*v);
b = y + (int)(1.772f*u);
r = r>255? 255 : r<0 ? 0 : r;
g = g>255? 255 : g<0 ? 0 : g;
b = b>255? 255 : b<0 ? 0 : b;
return 0xff000000 | (b<<16) | (g<<8) | r;
}
unsigned char * convertYUV420_NV21toRGB8888(unsigned char data[78080], int width, int height) {
int size = width*height;
int offset = size;
unsigned char * pixels = new unsigned char[size];
int u, v, y1, y2, y3, y4;
// i percorre os Y and the final pixels
// k percorre os pixles U e V
for(int i=0, k=0; i < size; i+=2, k+=2) {
y1 = data[i ]&0xff;
y2 = data[i+1]&0xff;
y3 = data[width+i ]&0xff;
y4 = data[width+i+1]&0xff;
u = data[offset+k ]&0xff;
v = data[offset+k+1]&0xff;
u = u-128;
v = v-128;
pixels[i ] = convertYUVtoRGB(y1, u, v);
pixels[i+1] = convertYUVtoRGB(y2, u, v);
pixels[width+i ] = convertYUVtoRGB(y3, u, v);
pixels[width+i+1] = convertYUVtoRGB(y4, u, v);
if (i!=0 && (i+2)%width==0)
i+=width;
}
return pixels;
}
int main(int argc, char *argv[])
{
QApplication a(argc, argv);
unsigned char * buffer;
unsigned char * image = NULL;
QPixmap pixmap;
QImage img(320, 122, QImage::Format_ARGB32_Premultiplied);
img.fill(QColor(Qt::white).rgb());
ifstream is;
is.open ("bunny.yuv", ios::binary );
// is.seekg (0, ios::end);
// length = is.tellg();
// is.seekg (0, ios::beg);
buffer = new unsigned char[78081];
is.read((char * )buffer,78080);
is.close();
/*
for (int x = 0; x < 10; ++x) {
for (int y = 0; y < 10; ++y) {
img.setPixel(x, y, qRgb(0, 0, 0));
}
}
*/
for(int i = 0; i < 78080; i++)
qDebug() << buffer[i]<< endl;
image = convertYUV420_NV21toRGB8888(buffer,320,122);
QByteArray byteImage((const char *)image);
pixmap.loadFromData(byteImage);
QLabel myLabel;
myLabel.setPixmap(pixmap);
myLabel.setGeometry(20,100,320,122);
myLabel.show();
return a.exec();
}
EDIT: I've added the right format and parenthesses. Still the same problem.
Kind regards,

Answer 1

And when you have done the calculation in Jason's post - the best format for the pixmap is QImage::Format_ARGB32_Premultiplied - the format is Blue byte Green byte Red byte 0xff

Answer 2

This won't do what you think it does:
r = y + (int)1.402f*v;
g = y - (int)(0.344f*u +0.714f*v);
b = y + (int)1.772f*u;
As you've missed parentheses and so cast your float constants to ints before the calculation.
And then having converted your YUV data into RGB packed into an int, you store that int into a char...
So:
unsigned char * pixels = new unsigned char[size];
Should probably be:
unsigned int* pixels = new unsigned int[size];
And obviously that affects the return type of the function too. You might also want to change the type of your YUV -> RGB function to unsigned as well, just for consistency.

Answer 3

In convertYUV420_NV21toRGB8888, pixels is an unsigned char array but you're trying to assign a int to it. All you will get is the low byte, and most of the bytes in your output will remain unset. You need to completely rethink the way you're writing the output.