AIPS HELP file for TVHLD in 31DEC22
As of Fri May 20 14:58:58 2022
TVHLD: Load an image to the TV with histogram equalization
INNAME Image name(name). blank=>any
INCLASS Image name(class). blank=>any
INSEQ 0.0 9999.0 Image name(seq. #). 0=>any
INDISK 0.0 9.0 Disk drive #. 0=>any
OUTNAME Output name (name).
OUTCLASS Output name (class).
OUTSEQ -1.0 9999.0 Output name (seq. #).
0 => highest unique
OUTDISK Output image disk drive #
0 => highest with room
BLC Bottom left corner out and
for computing histogram
TRC Top right corner out and
for computing histogram
TBLC 0.0 4096.0 Bottom Left Corner of image
TTRC 0.0 4096.0 Top Right Corner of image
TXINC 0.0 256.0 Load every TXINC'th column
TYINC 0.0 256.0 Load every TYINC'th row
NPOINTS 0.0 9000.0 Number of intensity bins
NX Histogram actual size
Use: TVHLD loads a map image into the TV with histogram equalization.
Interactive control of the pixel value range and other transfer
parameters is offered. The pixelization implied by the use of a
finite number of bins in the histogram and an even more finite
number of bins the conversion from histogram to list of
intensity ranges is obviated significantly by the use of linear
interpolation in the conversion to the list of ranges and in the
conversion of intensity values to equalized values.
TVHLD was initially written by Arnold Rots in 1983-1984.
Unfortunately, his version depended on several hardware
functions of the IIS Models 70 and 75 which are not available in
the X-Windows based TV programs. Therefore, it has been
completely re-written, in modern AIPS style, to offer a similar
functionality. Two related, non-interactive tasks are HISEQ
which does the full image in one histogram with the linear
method and an input PIXRANGE and AHIST which does histograms
within a box surrounding each pixel. They write out a new
equalized image. TVHLD does its histogram over the full window
specified by the adverbs and then loads it (or a sub-image of
it) to the TV. You may then interactively change the the low
and high values of the intensity range and select functions of
the histogram to use in the equalization. Various TV transfer
functions and enhancements are also offered to help study the
image. When you are happy you may EXIT, writing out a
histogram-equalized image or, if unhappy, you may ABORT and
avoid writing out an image.
INNAME......Image name (name). Standard defaults.
INCLASS.....Image name (class). Standard defaults.
INSEQ.......Image name (seq. #). 0 => highest.
INDISK......Disk drive # for the image. 0 => any.
OUTNAME.....Output image name (name) ' ' -> INNAME
OUTCLASS....Output image name (class) ' ' -> 'TVHLD'
OUTSEQ......Output image name (seq #) 0 -> highest+1
OUTDISK.....Output image disk drive #
BLC.........Bottom left corner of image to compute the equalizing
histogram and to go to output image.
TRC.........Top right corner of image to compute the equalizing
histogram and to go to output image. Note that only one
plane is done, so TRC(3) through TRC(7) are forced to
BLC(3) through BLC(7).
TBLC........Bottom left corner of TV image displayed. 0 -> centered
in BLC-TRC region.
TTRC........Top right corner of TV image displayed.
TXINC.......> 1 -> display only every TXINC column on TV
TYINC.......> 1 -> display only every TYINC row on TV
NPOINTS.....The histogram is computed in a large number (NX) of
boxes, but the ultimate division of the intensities is
done in NPOINTS boxes. < 100 -> 8192 but so many levels
will slow the task down. 1024 is a good number and the
task may limit NPOINTS still further.
NX..........The number of boxes used in the actual histogram.
0 -> 100000. If a large number is used, then the effect
of using functions like LOG on the histogram will be
TVHLD: Interactive image histogram equalization
REKATED PROGRAMS: HISEQ, AHIST
Histogram equalization is a traditional technique in image processing
to bring out fine detail where the histogram of intensities has many
pixels while obscuring detail where the histogram has few pixels. In
typical astronomy images, this emphasizes fine details in the image
values near zero and loses much of the intensity range at the highest
values. Nonetheless, it may be an interesting technique to apply to
images. The LOG histogram equalizes the histogram where one takes the
logarithm of the actual histogram counts before doing the
equalization. That leaves in much more detail of the higher levels in
the image. TVHLD begins in that mode but can be switched between LOG
and LINear modes.
The TV menu has two columns. On the left is
| OFF ZOOM | Turn off pixel-replication zoom from TVZOOM
| OFF TRANS | Turn off black & white enhancement from TVTRANSF
| OFF COLOR | Turn off color enhancement from TVPSEUDO and TVPHLAME
| TVZOOM | Adjust pixel-replication zoom
| TVTRANSF | Adjust the black & white transfer function
| TVPSEUDO | Adjust colors with numerous variations, types
| TVPHLAME | Adjust colors with flame-like scheme
| LOAD xxxx | Re-load TV with LIN (linear), LOG (log), SQRT (square
root), or LOG2 (more extreme log) transfer function
The right-hand menu contains
| ADJUST LOW | Adjust the lower intensity level included
| ADJUST HIGH | Adjust the higher intensity level included
| HISTO yyy | Equalize the histogram LINearly or the LOG of the
histogram or the 1/4, 1/2 (SQR), and 3/4 power of the
histogram in sequence
| EXIT | Exit task, writing out the output image
| ABORT | Exit task, not writing any image
You will probably find the ADJUST LOW is your most interesting option
and should examine all of the histogram modes. The HISTO options
allow you to reduce the influence of levels around zero, which in many
images completely dominate the histogram. The enhancement options
are just there to help you examine the image being prepared. They do
not affect the image that is written out.