FC - File Contouring

PURPOSE

Computes image contours by density foldover (cf 'DF') and subsequent line tracing. The result is a "visible" contour diagram contained in a file. The contours may optionally be superimposed on the original image.   Example.

SEE ALSO

FC E	[File Contouring - External contour levels]
DF	[Density Foldover]

USAGE

.OPERATION: FC

.INPUT FILE: PIC001
[Enter name of the image file to be contoured.]

.OUTPUT FILE: OUT001
[Enter name of image file where contoured file is to be put.

.NUMBER OF CONTOUR LEVELS: 5
[Enter number of contour levels desired. Note that these include the levels FMAX, FMIN which are often only assumed by one point each. Therefore, for a specification of 5 contours, only 3 contour lines will be visible.]

.OVERWRITE (Y/N): Y
[This option specifies the output file format: Enter 'Y' if you want to have the contour lines superimposed on the input picture; enter 'N' if you want to have the contour lines only.]

If 'Y' was specified for overwriting, SPIDER asks:

.WHITE, BLACK, OR ADJUSTED CONTOURS (W/B/A)?: A
[Enter 'W' for white contours (i.e., maximum density), 'B' for black contours (i.e., minimum density), or 'A' for contours of maximum or minimum density, depending on the density of the surrounding image.]

NOTES

1. White on a display corresponds to high density values.

2. This routine will fail for images where the range of values is <= .000001. Minima may be surrounded by contour lines, rather than having a line at the minimum level. This is an unavoidable feature of the density foldover algorithm used here.

SUBROUTINES

CNTRFL

CALLER

UTIL3