Help for GIACONDA

PURPOSE

Welcome to GIACONDA (Generator of Images of Accurate Color On Numerous Digital 
Apparatus).  GIACONDA transforms images taken through several filters into a
color image in which designated spectra ("special colors") are reproduced
accurately.  Special colors are defined, modified and examined using VICAR
program LEONARDO.  At this time, the only output device supported by this
program is  the CONRAC 7211 long persistence color monitor. 

EXECUTION

  The program is executed by specifying up to eight half-word images (registed,
FICOR'ed and VGRFIX'ed, or GALSOS'ed) taken through different filters, up to
ten special colors, and, optionally, three output files (red, blue, and green),
a weight for each special color (applied to a least-square fit), and a scale
factor for the input images, and an image display device.  The program will
display the resulting transformation matrix (input dn to output intensity) and,
if output files have been specified, will generate images which may be input to
the specified device. 

  This program reads the special colors from a file pointed to by the 
logical name, SCFNAME.  The file is a 100-line by 70-sample VICAR image
file, which must be created outside of this program.  The same file is read
and written by LEONARDO to define these colors. 

  If the program indicates "NO UNIQUE SOLUTION", there are several possible
reasons for the failure:
  1) Two of the input images were taken through the same filter.
  2) One of the special colors is a linear combination of the others.
  3) One of the special-color spectra does not overlap any of the filter
  	 responses.
  4) One of the filter responses does not overlap any of the special-color
  	spectra.
  5) One of the filters passes nothing in the visible (e.g., VGR UV).

OPERATION

  GIACONDA uses the classical photo-reproduction solution (with a slight
modification) to accurately reproduce selected ("special") colors.  For a
given pixel,  the I/F value for each of n filters is the sum of the tristimulus
values for that pixel, and, therefore, each of the tristimulus values of a
given pixel may be written as a linear combination of the I/F values obtained
from each filter.  If these equations (with unknown coefficients) are written
down for a n special colors, the we have, for each chromaticity coordinate, n
equations with n unknowns.  Therefore, we can solve for the unknown
coefficients, and we have the tristimulus values of a pixel as a function of
the I/F values from each filter.  And, in fact, any linear combination of
special colors will be accurately reproduced with this solution.  If there are
more special colors than filters, a least-squares fit solution may be applied,
as is done by this program. 

  The next step is to convert the tristimulus values to device inputs.  A
monitor's intesity is equal to the sum of the intensities of the three
primaries, and, therefore, the intensity for each phosphor can be written as a
linear combination of the desired tristimulus values.  Intensity is then
converted to input dn by 

  			DN = I ** 1/2.6,

the 2.6 in the exponent being good for all contemporary CRT's.  (It is assumed 
here that the monitor has been adjusted so the zero dn produces 0+ intensity.)
The final dn values are then normalized so that the highest expected input-
image dn produces a monitor dn of 255 (see SCALE), and out-of-range values are 
set at 0 or 255.  This exponential results in some surprising effects (e.g.,
bright skies due to residual dark current).  Only a proportional stretch on the
output images will maintain the proper hues and saturations.  THIS EXPONENT IS
NOT APPLIED IF PARAMETER, DEVMAT, IS SPECIFIED.

  The device response for a film recorder is a tougher nut to crack.  Although 
this program has hooks for that capability, it is not implemented at this time 
(see memo MSD:384-86-105, "Accurate Color Reproduction", R. Brill).

EXAMPLE

  In the following examples the user creates output files, OUT.*, using input 
images INP.*, and special colors, CLOUDS, VOLCANOES, SULPHUR, and SAND, with 
corresponding weights, 3, 2, 1, and 1, respectively.  He uses wants input dn's 
of 10000 to be the maximum brightness (default).

  VICAR>GIACONDA INP=(INP.ORA,INP.CLR,INP.GRE)   VICAR>+ OUT=(OUT.RED,OUT.GRE,OUT.BLU)   VICAR>+ SCFNAME=(COLORS.DAT)   VICAR>+ COLORS=(CLOUDS,VOLCANOES,SULPHUR,SAND) WEIGHTS=(3.,2.)
 

WRITTEN BY: 		   R. BRILL, 20 JUNE, 1986

COGNIZANT PROGRAMMER:	   R. BRILL, 20 JUNE, 1986

Made portable for UNIX ... J. TURNER (CRI),  5 Sept 1994

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