Haha, I went through his 6 weeks ago, but I only needed the Y channel.
The frame is not laid out like RGB. This is for legacy reasons. Black and White
TV presented a black and white frame (Y) when color TV was added, it was added
in a backwards-compatible way, with that data between the Y frames. SO what you
have are actually 3 images per frame - the width x height B&W Y channel then a
subsampled Cb and Cr. Cb and Cr as subsampled by a factor of two, meaning you
have:
[Y (width*height)] [Cb (width/2*height/2)] [Cr (width/2*height/2)]
so your y_ is right,
but u_ is at (width*height) + (y *(width/2)) + x/2
but v_ is at (width*height) + ((width*height)/4) + (y *(width/2)) + x/2
Yes, this means that U and V are used for 4 pixels, but the Y channel is pixel
for pixel.
________________________________
From: Rayner Pupo <rpgo...@uci.cu>
To: interest@qt-project.org
Sent: Friday, March 14, 2014 11:29 AM
Subject: [Interest] QVideoFrame and YUV question
Hi, I'm trying to create a QImage from a QVideoFrame but my video has YUV420P
format so converting it's not easy for me at all. By using a snippet from
histogram class from the player example provided by Qt I was able to read each
pixel on the frame but my question is: who can I decompose Y, Cb and Cr values
from a single uchar?
This is how to I'm iterating over the video frame bits.
if (videoFrame.pixelFormat() == QVideoFrame::Format_YUV420P) {
QImage nImage(videoFrame.width(), videoFrame.height(),
QImage::Format_RGB32);
uchar *b = videoFrame.bits();
for (int y = 0; y < videoFrame.height(); y++) {
uchar *lastPixel = b + videoFrame.width();
int wIndex = 0;
for (uchar *curPixel = b; curPixel < lastPixel; curPixel++) {
double y_ = *curPixel;????????
double u_ = ???????????;
double v_ = ???????????;
r = y_ + 1.402 * v_;
g = y_ - 0.344 * u_ - 0.714 * v_;
b = y_ + u_ * 1.772;
nImage.setPixel(wIndex, y, qRgb(int(r), int(g), int(b)));
++wIndex;
}
b += videoFrame.bytesPerLine();
}
return nImage;
}
________________________________________________________________________________________________
I Conferencia Cient�fica Internacional UCIENCIA 2014 en la UCI del 24 al 26 de
abril de 2014, La Habana, Cuba. Ver http://uciencia.uci.cu
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