Single Image Processing with Immediate Mode

This tutorial demonstrates single image processing with immediate mode.

The tutorial uses the following pipeline as an example:

(source image) -> [Median 3x3] -> [Equalize Hist] -> [Canny Edge Detector] -> (edges)

VisionWorks has two modes for vision primitive execution : immediate mode and graph mode. In immediate mode, primitives are executed directly by calling a function (like in OpenCV or NPP). The mode is useful for single image processing.

First, the source image is loaded from a file using NVXIO library. The NVXIO library must be initialized prior to this call.

vx_image source = nvxio::loadImageFromFile(context, sourceUri, VX_DF_IMAGE_U8);

Second, the output edges image is created, as well as an dditional vx_threshold object that is used for CannyEdgeDetector primitive.

vx_uint32 width, height;
vxQueryImage(source, VX_IMAGE_ATTRIBUTE_WIDTH, &width, sizeof(width));
vxQueryImage(source, VX_IMAGE_ATTRIBUTE_HEIGHT, &height, sizeof(height));

vx_image edges = vxCreateImage(context, width, height, VX_DF_IMAGE_U8);

vx_threshold hyst = vxCreateThreshold(context, VX_THRESHOLD_TYPE_RANGE, VX_TYPE_INT32);
vx_int32 lowerThresh = 230, upperThresh = 250;
vxSetThresholdAttribute(hyst, VX_THRESHOLD_ATTRIBUTE_THRESHOLD_LOWER,
                        &lowerThresh, sizeof(lowerThresh));
vxSetThresholdAttribute(hyst, VX_THRESHOLD_ATTRIBUTE_THRESHOLD_UPPER,
                        &upperThresh, sizeof(upperThresh));

Finally, the VisionWorks primitives are called in immediate mode. Note that intermediate data objects are created as normal images.

vx_image filtered = vxCreateImage(context, width, height, VX_DF_IMAGE_U8);
vx_image equalized = vxCreateImage(context, width, height, VX_DF_IMAGE_U8);

vxuMedian3x3(context, source, filtered);
vxuEqualizeHist(context, filtered, equalized);
vxuCannyEdgeDetector(context, equalized, hyst, 3, VX_NORM_L1, edges);

vxReleaseImage(&filtered);
vxReleaseImage(&equalized);