Problem showing raw images

[wkit23]

Hi, I'm new to Qt4. I'm currentl using Qt as part of my project, but I'm facing problem using it. My project consist of reading a raw image, and then display it.

Since my raw image is in short byte array, I can't seems to show the image correctly using QImage. However, I manage to get the image to output correctly with OpenGL glDrawPixels, but the process is kinda sluggish and eats quite a lot of resources. Since I just wanna show the image, I was searching for a better way.

Here's my OpenGL code.

void pktGLWidget::paintGL()
{
   glClear(GL_COLOR_BUFFER_BIT);
   glPixelStorei(GL_UNPACK_ALIGNMENT, 1);
   glDrawPixels(imgWidth, imgHeight, GL_LUMINANCE, GL_BYTE, glBuffer);
   glFlush();
}

void pktGLWidget::paintGL()
{
   glClear(GL_COLOR_BUFFER_BIT);
   glPixelStorei(GL_UNPACK_ALIGNMENT, 1);
   glDrawPixels(imgWidth, imgHeight, GL_LUMINANCE, GL_BYTE, glBuffer);
   glFlush();
}

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And here's my QImage code, which can't seems to work properly.

void pktQImage2D::processBuffer()
{
  m_Image = QImage((uchar *) pixelData, imgWidth, imgHeight, QImage::Format_Mono);
}

void pktQImage2D::processBuffer()
{
  m_Image = QImage((uchar *) pixelData, imgWidth, imgHeight, QImage::Format_Mono);
}

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[e8johan]

You will have to write your own image loading class. How to do it is shown here: http://doc.trolltech.com/qq/qq17-imageio.html . There is a free lib to support reading raw images here: http://www.cybercom.net/~dcoffin/dcraw/ .

[wkit23]

Well, actually it's not the camera's raw image data that I was dealing with. I've written a class to read and extract the image's data, which is in short byte array, with low values is white and higher values is black. It's just a pure black and white image.

I've manage to make a class to view the image in OpenGL, but the process really seems slow and sluggish, and it's eating my resources whenever I drag the window. Since I only want to view the images, I was looking for a much better way. I've try loading the data using QImage::fromData but the output is some sort of rubbish data. Anyone has better ideas?

[Raistlin]

Something like this should work, I use it this way to use imporant my own TIFF images.

//Raw data and dimensions of image
unsigned short* data;
int dim[2];
 
QImage rawImage(dim[1], dim[0], QImage::Format_Indexed8);
 
rawImage.setNumColors(256);
for (int i = 0; i < 256; i++ ) 
	rawImage.setColor( i, qRgb( i, i, i )) ;
 
for (int i = 0; i < dim[0]; i++)
{
	unsigned char* image = rawImage.scanLine(i);
	for (int j = 0; j < dim[1]; j++)
		image[j] = data[i * dim[1] + j] / 256;
}

//Raw data and dimensions of image
unsigned short* data;
int dim[2];

QImage rawImage(dim[1], dim[0], QImage::Format_Indexed8);

rawImage.setNumColors(256);
for (int i = 0; i < 256; i++ ) 
	rawImage.setColor( i, qRgb( i, i, i )) ;

for (int i = 0; i < dim[0]; i++)
{
	unsigned char* image = rawImage.scanLine(i);
	for (int j = 0; j < dim[1]; j++)
		image[j] = data[i * dim[1] + j] / 256;
}

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You have to convert to unsigned char to be able to display it.

You can then use QPixmap::fromImage() and QLabel::setPixmap() to display the image on a QLabel.

[wkit23]

So far, I've tried different methods for displaying my image. Note that raw formats I mean here is not the digital camera's RAW format. It's actually bytes of data (grayscale values) that I decoded.

I've tried openGl to display the images. glDrawPixel functions is slow, and if the images is large enough, u'll have a hard time to manipulate it. So I try to implement glTexture, the result is a whole lot faster. But the problem came when the images contains size not power of two, which texture can't be loaded properly.

So, I recheck back my QImage implementation, and after some time, I've found out I didn't setup the QImage properly, and didn't build up the neccesaly grayscale colormap. So far with some simple data I test, so far so good. However, the problem came when I try a large image with 2500*2048. Somehow the image become back to jerky again...

Here's my implementation

void pktDisplayWidget::setInternalImage()
{
	m_Image = new QImage(output, imgWidth, imgHeight, QImage::Format_Indexed8);
 
	//setup the grayscale color table
	m_Image->setNumColors(256);
	for (int i=0; i<256; i++)
		m_Image->setColor(i, qRgb(i, i, i));
 
	if (m_Image->isNull())
		QMessageBox::warning(this, tr("Error in pktDisplayWidget"), 
			tr("Unable to create the image object."));
 
	if (swap)
		m_Image->invertPixels(QImage::InvertRgb);
 
	//pass the image to the label (this)
	this->setPixmap(QPixmap::fromImage(*m_Image));
	this->adjustSize();
}

void pktDisplayWidget::setInternalImage()
{
	m_Image = new QImage(output, imgWidth, imgHeight, QImage::Format_Indexed8);

	//setup the grayscale color table
	m_Image->setNumColors(256);
	for (int i=0; i<256; i++)
		m_Image->setColor(i, qRgb(i, i, i));

	if (m_Image->isNull())
		QMessageBox::warning(this, tr("Error in pktDisplayWidget"), 
			tr("Unable to create the image object."));

	if (swap)
		m_Image->invertPixels(QImage::InvertRgb);

	//pass the image to the label (this)
	this->setPixmap(QPixmap::fromImage(*m_Image));
	this->adjustSize();
}

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[wkit23]

I've found the problem. It appears that my width and height are exchanged when I'm decoding the raw image... Strangely odd since other smaller images shows no problem at all...