[PyQt] Pixel Manipulation Very Slow?

zhangmdev at gmail.com zhangmdev at gmail.com
Tue Aug 24 20:26:01 BST 2010

Also there is some experiment about how to get image data from PyQt to  
C/C++ via SIP. Must let the method receive void*

void Word::addColor(void *d)
unsigned char* bits = (unsigned char *)d;

for(int j=0; j< _img_h; j++) {
for(int i=0; i< _img_w; i++) {

_color[(j*_img_w+i)*4] = *bits/255.f;//Blue
_color[(j*_img_w+i)*4+1] = *bits/255.f;//Green
_color[(j*_img_w+i)*4+2] = *bits/255.f;//Red
_color[(j*_img_w+i)*4+3] = *bits/255.f;//Alpha


I convert the unsigned char array into a float array. In python


Seems it is working.


On Aug 25, 2010 2:06am, zhangmdev at gmail.com wrote:
> Hi,

> I tried SIP to do the pixel manipulation in C/C++. Word is the class I  
> adopted from SIP hello world example. Must have a method return void*

> void *Word::display()
> {
> for(int j=0; j for(int i=0; i _data[(j*w+i)*4] = 127;//Blue
> _data[(j*w+i)*4+1] = 127;//Green
> _data[(j*w+i)*4+2] = 255*_red;//Red
> _data[(j*w+i)*4+3] = 0;//Alpha

> }
> }
> return _data;
> }

> actually it returns char* _data, the pixels. I found the order of color  
> is a bit interesting, first the Blue, second is Green, third is Red, then  
> Alpha. The pointer will be sip.voidptr In python, I think.

> image = QImage(self.a.display() , w, h, QtGui.QImage.Format_RGB32)
> painter.drawImage(0, 0, image)

> Now the speed is quite interactive.

> zhang
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