IMAGE_EDGE
Edge Detection in Images

IMAGE_EDGE is a FORTRAN77 library which demonstrates the detection of edges in an image.

NEWS is a particularly simple edge detection scheme, which compares the North, East, West, and South neighbors of a pixel to determine if the pixel lies along an edge.

There are many sophisticated edge detection algorithms, and MATLAB has many of them built into its image processing toolbox. The purpose of these examples is simply to demonstrate how a simple version of such edge detection schemes works.

Licensing:

The computer code and data files described and made available on this web page are distributed under the GNU LGPL license.

Languages:

IMAGE_EDGE is available in a C version and a C++ version and a FORTRAN77 version and a FORTRAN90 version and a MATLAB version.

EDGE, a FORTRAN77 library which defines some test functions in 1D, 2D and 3D for the detection of edges or discontinuities. It uses GNUPLOT to display the jumps in curves and surfaces.

IMAGE_COMPONENTS, a FORTRAN77 library which seeks the connected "nonzero" or "nonblack" components or "segments" of an image or integer vector, array or 3D block.

IMAGE_DENOISE, a FORTRAN77 library which applies simple filtering techniques to remove noise from an image.

PBMA_IO, a FORTRAN77 library which handles the ASCII Portable Bit Map (PBM) format.

PGMA_IO, a FORTRAN77 library which handles the ASCII Portable Gray Map (PGM) format.

• image_edge.f, the source code.
• image_edge.sh, commands to compile the source code.

Examples and Tests:

• image_edge_prb.f, a sample calling program.
• image_edge_prb.sh, commands to compile and run the sample program.
• image_edge_prb_output.txt, the output file.
• coins.ascii.pgm, an ASCII PGM file containing a grayscale image of coins.
• coins.png, a PNG version of the image.
• coin_edges.ascii.pbm, an ASCII PBM file containing a bitmap image of coins.
• coin_edges.png, a PNG version of the image.

List of Routines:

• CH_CAP capitalizes a single character.
• GET_UNIT returns a free FORTRAN unit number.
• GETINT reads an integer from a file.
• I4MAT_HISTOGRAM computes a histogram of the elements of an I4MAT.
• NEWS demonstrates the NEWS stencil for edge detection.
• PBMA_WRITE writes an ASCII portable bit map file.
• PBMA_WRITE_DATA writes the data of a PBMA file.
• PBMA_WRITE_HEADER writes the header of a PBMA file.
• PGMA_READ_DATA reads the data in an ASCII PGM file.
• PGMA_READ_HEADER reads the header of an ASCII PGM file.
• S_EQI is a case insensitive comparison of two strings for equality.
• S_TO_I4 reads an I4 from a string.
• TIMESTAMP prints the current YMDHMS date as a time stamp.
• WORD_NEXT_RD "reads" words from a string, one at a time.

You can go up one level to the FORTRAN77 source codes.