vil_algo : Computational Imaging Library

Some simple algorithms for manipulating images. Note that the argument order is typically of the form vil_f(src_im,dest_im,params). Examples include

• vil_convolve_1d - Convolve with 1D filter - all manner of edge effects catered for
• vil_convolve_2d - Convolve with 2D filter (no edge effects catered for yet!)
• vil_correlate_1d - Similar to vil_convolve_1d but with reversing the kernel
• vil_correlate_2d - Similar to vil_convolve_2d but with reversing the kernel
• vil_gauss_filter_gen_ntap - Generate an n-tap FIR filter from a Gaussian function
• vil_gauss_filter_5tap - Apply 1d Gaussian filter using 5 element kernel
• vil_gauss_filter_1d - Apply 1d Gaussian filter of arbitrary SD and kernel width
• vil_gauss_filter_2d - Apply 2d Gaussian filter of arbitrary SD and kernel width
• vil_exp_filter_i - Apply exponential filter along i axis (fast recursive method)
• vil_exp_filter_j - Apply exponential filter along j axis (fast recursive method)
• vil_exp_filter_2d - Apply exponential filter along i and j (fast recursive method)
• vil_exp_grad_filter_i - Apply exponential gradient filter along i axis (fast recursive method)
• vil_exp_grad_filter_j - Apply exponential gradient filter along j axis (fast recursive method)
• vil_sobel_3x3 - to generate X/Y gradient images using 3x3 Sobel operators
• vil_gauss_reduce - smooth and sub-sample to produce half sized image
• vil_median - Compute median over area described by vil_structuring_element
• vil_fft_2d_fwd,bwd - Perform in-place 2D FFT on an image of a complex type
• vil_suppress_non_max_3x3 - Zero all pixels which are not local maxima
• vil_corners - Harris cornerness operator
• vil_find_peaks - Locate local peaks in an image
• vil_orientations - Compute angle and edge magnitude at each pixel
• vil_distance_transform - Apply distance transform to images
• vil_histogram_equalise - Replace every pixel by its intensity rank
• vil_suppress_non_max_edges - Compute gradient magnitude and zero any non-maximal values

See also the vipl library for a more generic image processing interface and more image processing algorithms.

Morphological functions (using vil_structuring_element)

• vil_binary_erode
• vil_binary_dilate
• vil_binary_opening
• vil_binary_closing
• vil_greyscale_erode
• vil_greyscale_dilate
• vil_greyscale_opening
• vil_greyscale_closing
• vil_median

Other related maths functions

• vil_histogram(image,hist,min,max,nbins) : Compute histogram of image values
• vil_histogram_byte(image,histo) : Compute histogram from byte image

The boundaries of thresholded regions can be found using

• vil_find_4con_boundary_above_threshold
• vil_find_4con_boundary_below_threshold (Given a point inside a closed, 4-connected region defined by a threshold, these functions find the 4-connected boundary pixels of the region)

• vil_trace_4con_boundary : Traces around 4 connected regions in bool image
• vil_trace_8con_boundary : Traces around 8 connected regions in bool image
• vil_blob_finder : Class to find all connected regions in an image

• vil_tile_images : Generate single image by tiling together a set of images

For your ease of use, all vil functions and methods adhere to the following parameter conventions:

• Index types - All pixel index and image size types are unsigned.
• Specifying a pixel - func(i,j) assumes plane 0 or func(i,j,p)
• Specifying a window - func(i0,ni,j0,nj) window includes all planes.

Examples

There are plenty of working examples in the examples subdirectory - these can be treated as a mini-tutorial.

Lead

Ian Scott is responsible for co-ordinating significant changes to vil_algo. http://sourceforge.net/sendmessage.php?touser=261110