Extract pixel values from a bitmap in Qt
December 24, 2012
The first step in writing an image processing program is usually extracting the image data from a file container such as a bitmap or jpeg file. Using Qt, the QImage class makes this easy. The QImage can open/save directly to bmp, jpeg, and other common container formats. Once a file has been opened into an instance of a QImage, the RGB pixel values can be extracted into a luminance array for processing.
Here is a code example for extraction. In this case, an array of 32-bit value is used for storage even though only the lower byte has a value.
The RGB values are mapped to the luminance vector of the YUV color space.
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void ImageUtils::getPixelsFromBmpIntoLuminance(QImage * image, int *dstPtr) { int width = image->width(); int height = image->height(); char * rgbValues = (char *) image->scanLine(0); QImage::Format format = image->format(); int x = 0; int y = 0; int b = 0; int bv = 0; int rv = 0; int gv = 0; int xOffset = 0; if (format == QImage::Format_Indexed8) { for (y = 0; y < height; y++) { for (x = 0; x < width; x++) { xOffset = y * width; *(dstPtr+xOffset +x ) = rgbValues[b] & 0xff; b ++; } } } else if ( format == QImage::Format_RGB32) { for (y = 0; y < height; y++) { for (x = 0; x < width; x++) { xOffset = y * width; bv = ((int)rgbValues[b + 0] & 0xff) * 114; gv = ((int)rgbValues[b + 1]& 0xff) * 587; rv = ((int)rgbValues[b + 2]& 0xff) * 299; *(dstPtr+xOffset +x ) = ((((bv + rv + gv) / 1000))) & 0xff; b += 4; } } } } |
Entry filed under: Image Processing, Qt. Tags: .