Using a 2d data array to create an image

[dbrmik]

Hi

I am new to Qt and windows types programs in general. I have a 2d array of data (could either be 32bit float or char ). I would like to use this data to create an image to display in a window. I would be grateful if somebody could point me in the right direction

Best Regards

[spirit]

look at this method QImage::fromData or this QPixmap::loadFromData.

[dbrmik]

Thanks, but the data is raw just a 2d array of floats (could be chars), it does not have a header. I am really stuck on this. Also how do I display this image in a window, what do I have to do to achieve this (justy the basics)?

Thanks

[spirit]

for displaying an image you can use, for example, QLabel::setPixmap.

how do you get raw data?

[dbrmik]

Thanks spirit.

The data is loaded from a file into a 2d array. The data represents a memory dump of a Radars B-Plane. We have a algorithm which sharpens up radar displays and I want to create a simulator which shows a 'before' and 'after' image. I am not familar with qt or gui's , so all this talk of widgets etc is a bit confusing at the moment. All i want, as a first attempt is a way to create an image/picture of this data and display it in some window.

Thanks once again

[spirit]

this file where picture is stored has only image data or someother data too?

[dbrmik]

Hi

The file just contains raw data samples obtained using an analog to digital converter

Thanks

[spirit]

how do you know that raw data has correct image? I'm confused.

[dbrmik]

Hi

The data are just samples, each samples amplitude is to represent a pixels intensity in the final image . Essentially all I have is 2d array of data, from which I want to create an image for display. I was looking at QImage as a possible solution, as you can load the QImage buffer with data using scanline, but I couldnt get this to work.

Thanks

[dbrmik]

Hi

I suppose you could look at the problem this way. Consider a 2d array of chars of say 200 rows x 200 columns. Every element in a row has the same value, this value increases by one for every row. So for example each sample in the first row might have sample value of 1, the second row 2 and so on until we get to the final row which would have sample value of 200. If you created an image of this 2d array you would expect to see horizontal lines of increasing intensity (if we assume a grayscale image). How could I create such an image using QT and display this on a label/widget

Thanks for your time

[spirit]

then use QImage this class allows to access to pixels.

[dbrmik]

Yes, I have used QImage and loaded the buffer with my data. How di I subsequently display this QImage on a widget?

[SunnySan]

I am also looking at similar problem (moving image )

so in the designer create a Qlabel
then access Qlabel ui.labelName->setQimage or something like that
then modify the QImage using QPainter

then update the

I found an example in the demo to draw a ball with gradient

pixmap = QPixmap(100, 100);
         pixmap.fill(Qt::transparent);
 
         QRadialGradient gradient(50, 50, 50, 50, 50);
         gradient.setColorAt(0, QColor::fromRgbF(1, 0, 0, 1));
         gradient.setColorAt(1, QColor::fromRgbF(0, 0, 0, 0));
         QPainter painter(&pixmap);
         painter.fillRect(0, 0, 100, 100, gradient);
 
         channelImage = pixmap.alphaChannel();
         update();

pixmap = QPixmap(100, 100);
         pixmap.fill(Qt::transparent);

         QRadialGradient gradient(50, 50, 50, 50, 50);
         gradient.setColorAt(0, QColor::fromRgbF(1, 0, 0, 1));
         gradient.setColorAt(1, QColor::fromRgbF(0, 0, 0, 0));
         QPainter painter(&pixmap);
         painter.fillRect(0, 0, 100, 100, gradient);

         channelImage = pixmap.alphaChannel();
         update();

To copy to clipboard, switch view to plain text mode 

I am not sure yet if we can modify the Qpainter dot by dot
This may help

[wysota]

Yes, I have used QImage and loaded the buffer with my data. How di I subsequently display this QImage on a widget?

Transform it to QPixmap and display using QLabel.

[SunnySan]

the problem seems to be how to modify the QPixmap having a set of coordinates X,Y
is there any good example around?

[wysota]

The pixmap is used to display data. QImage is used to manipulate data. Use QImage to change pixel colours and a pixmap created from it to display the image.

[dbrmik]

Hi

I've made a little progress, however I think I need halep with the colour map. I have created an 8bit image and filled all values in each row with a constant.

QImage BPlaneI(rows,cols,QImage::Format_Indexed8);//8 bit image
loadImageData(ch_ptr,rows,cols,&BPlaneI);

Then converted to pixamp and displayed on a label

QPixmap qp(rows,cols);
qp.fromImage(BPlaneI,Qt::AutoColor);
QLabel l;
l.setPixmap(qp);
l.show();

However the label display is entirely black, I have also queried the depth of the pixmap and this shows a depth of 32, I was expecting 8?

I would be grateful if anybody had any ideas why this might be the case

Best regards

[wysota]

8bit images use a colour look-up table thus the value you put as pixel data is the index in the colour table which is probably empty thus you get all black. QPixmap will always be 32b. Reading documentation really doesn't hurt - try it.

[dbrmik]

Thanks wysota, yes RTFM, i've said that in the past

I assume that the conversion from 8bpp to 32bpp doesnt scale the pixel values and that is why my label is black?

Do I have to create a colour table, how do I associate the colour table with my pixmap? I am confused.

Best Regards

[dbrmik]

Still having problems with this, I have realised I need to create a colortable which I have populated with 'yellow' for all entries, so expecting a yellow image. The image is still black.
My code is below

QImage BPlaneI(ch_ptr,rows,cols,QImage::Format_Indexed8);//8 bit image
BPlaneI.setNumColors(256);
loadImageData(ch_ptr,rows,cols,&BPlaneI);//load image buffer from ch_ptr

for (int i=0; i<255; i++)
{
BPlaneI.setColor(i,Qt::darkYellow);
}

QPixmap qp(rows,cols);
qp.fromImage(BPlaneI,Qt::AutoColor);

QLabel l;
l.setPixmap(qp);
l.show();

Really stuck with this one, any ideas would be greatly appreciated

Thanks