M_pixel__readgif Module

readgif(3f) - [M_pixel__readgif] read a GIF file
(LICENSE:PD)

character(len=*), intent(in) :: filename
integer, intent(in)          :: num_image
integer, intent(out), allocatable :: image(:,:)
integer, intent(out)         :: iostat
real   , allocatable, intent(out) :: color_map(:,:)
logical, intent(in), optional :: verbose

read the num_image'th gif image from filename into arrays image and color_map

filename    input file
num_image   number of image required
image       Image data returned
iostat      I/O error number, =0 if ok
color_map   RGB for each level, range 0.0 to 1.0
verbose     .true.for verbose output

Sample program:

   program demo_readgif
   use M_pixel__readgif, only : readgif
   use M_pixel__writegif, only : writegif
   implicit none
   character(len=*),parameter :: filename='boxes.gif'
   integer                    :: num_image=1
   integer,allocatable        :: image(:,:)
   integer                    :: iostat=0
   real,allocatable           :: color_map(:,:)
   integer,allocatable        :: color_map2(:,:)
   logical                    :: verbose=.true.
   integer                    :: i,ii,jj
   call readgif(filename,num_image,image,iostat,color_map,verbose)
   if(iostat.ne.0)then
      write(*,*)'*demo_readgif* could not read GIF file ',trim(filename)
      stop
   endif

   write(*,*)'SIZE OF IMAGE =',size(image)
   do i=1,rank(image)
      write(*,*)'RANK OF IMAGE=',i,size(image,dim=i)
   enddo

   write(*,*)'SIZE OF COLORMAP=',size(color_map)
   do i=1,rank(color_map)
      write(*,*)'RANK OF COLORMAP=',i,size(color_map,dim=i)
   enddo

   ! convert between colormap types
   ! writegif uses an integer colormap, values 0 to 255
   ! readgif  uses real values 0.0 to 1.0
   ii=size(color_map,dim=1)
   jj=size(color_map,dim=2)
   if(allocated(color_map2))deallocate(color_map2)
   allocate(color_map2(ii,0:jj-1))
   color_map2=255*color_map

   ! change color and write standard gif file
   where (image.eq.1) image=4
   call writegif('boxes_new.gif',image,color_map2)

   end program demo_readgif

Jos Bergervoet, Van Snyder, Maurizio Cremonesi, Clive Page, and others

This module contains a subroutine readgif(3f) which can read GIF files
of types Gif87a and Gif89 (and maybe others). The code comes from
various authors, see comments below. This version was put together
by Clive Page who has put it into the public domain.