NAME

hafton -- draw a half tone picture of an image

USAGE

hafton image

PARAMETERS

image

Two dimensional image or image section to be plotted.

z= 0.0, z2 = 0.0

The minimum (z1) and maximum (z2) intensities to be mapped. If left at the default values of 0.0, the full intensity range will be mapped.

nlevels = 0

The number of intensities levels to be shown. If nlevels = 0 or 1 , the maximum of 16 levels is used.

mapping_function = "linear"

A string specifying the image intensity to half tone mapping function. The default is linear mapping between z1 and z2 . For other choices, see the description section below.

contrast = 0.25

Positive or negative contrast. Negative constrast is indicated by setting contrast to a negative number. The magnitude of contrast is not important unless mapping_function = crtpict .

perimeter = yes

Should a crtpict perimeter with labelled tickmarks be drawn around the plot?

device="stdgraph"

Output device for plot.

title = "imtitle"

The title to be centered above the plot. By default, the title string from the image header is used.

xres = 64, yres = 64

The input image is block averaged or subsampled to this resolution.

preserve = yes

If preserve = yes, the aspect ratio of the image is preserved when achieving the resolution specified by xres and yres .

subsample = no

Should the image be subsampled (as opposed to block averaged) to achieve the specified resolution?

vx= 0.0, vx2 = 0.0, vy1 = 0.0, vy2 = 0.0

The device viewport, in normalized device coordinates (from 0.0 to 1.0 inclusive). If not specified by the user, the plot is centered on the viewport.

fill = no

Should the plot fill the viewport regardless of the device aspect ratio?

append = no

Append to an existing plot?

DESCRIPTION

Task hafton draws a half tone picture of an IRAF image, where varying intensities in the image are represented by areas of varying darkness on the plot. Six different mapping functions are available; the desired mapping function is selected with the mapping_function string. The types of mapping are:

   linear
   exponential - emphasizes high intensity values.
   logarithmic - emphasizes low intensity values.
   sinusoidal  - emphasizes mid-range values.
   arcsine     - extreme values emphasized at the expense of mid-range.
   crtpict     - linear mapping centered on median intensity.  The slope of
		 the function is modified by \fBcontrast\fR.

If the device viewport is not set by the user, hafton automatically sets a viewport centered on the output device. The default value of fill=no means the viewport will be adjusted so that equal numbers of image pixels in x and y will occupy equal lengths when plotted. That is, when fill=no , a unity aspect ratio is enforced, and square images are represented as square plots regardless of the device aspect ratio. On devices with non square full device viewports (e.g., the vt640), a square image will appear extended when fill=yes .

EXAMPLES

1. Image "crab.6563" is plotted in negative contrast, with linear mapping between the minimum and maximum image pixel.

cl> hafton crab.6563 contrast=-1

2. The image is plotted in negative contrast using the same mapping function as used by the crtpict task. The resulting plot is in negative contrast.

cl> hafton crab.6563 mapping_fun=crt contrast =-0.25

TIME REQUIREMENTS

To produce a hafton plot on the terminal takes just under 9 cpu minutes. If the output device is the imagen or versatec (or another nspp device) the total cp time is about an hour.

BUGS

A large number of plotter instructions ( > 100,000 polylines) is generated per frame for square images.