;----------------------------------------------------------------------------
; This file is a piece of IDL code that can be executed from
; the IDL command line by typing:   .run readgif.pro
; (assuming that's the name of this file in your directory)
;
; You'll need to change the FNAME to read each desired gif file.
; This code only works properly for the black-and-white versions.
;
; *** THE BEST ONES seem to be "red1" and "blue2" !!!
;
; The result of running this are several arrays in IDL's memory:
;
;  xpix:   1D array of x-pixel values (size: nxpix)
;  ypix:   1D array of y-pixel values (size: nypix)
;  bright: 2D array of "brightness" values (size: nxpix by nypix)
;----------------------------------------------------------------------------

   FNAME = 'sun_red1_bw.gif'

   read_gif,FNAME,data,rr,gg,bb
   dummy = SIZE(data)
   nxpix = dummy(1)
   nypix = dummy(2)

   print,' '
   print,' nxpix,nypix = ',nxpix,nypix
   print,' '

   bright = dblarr(nxpix,nypix)
   for i=0,nxpix-1 do begin
    for j=0,nypix-1 do begin
      bright(i,j) = double(rr(data(i,j)))
    endfor
    if ((i mod 50) eq 0) then print,i,' / ',(nxpix-1)
   endfor

   print,' '
   print,' done setting up main data array '
   print,' '

; Next you need to find the coordinates of the center of the Sun,
; as well as set the solar radius (all in units of pixels), and
; determine "mu" (the cosine of the angle "theta" in the 1st diagram
; of the solar_overview handout) at each point in the image.

; You'll probably find out on your own that the outermost EDGES of
; the images are of lesser quality than the interior regions.  You
; will get the best results by simply ignoring an outer rectangle
; that is 100 pixels "thick" on all sides.

; Finally, you need to determine the derivative dI/d(mu).

   end