; $Id: read_gif.pro,v 1.21 2004/01/21 15:55:00 scottm Exp $ ; ; Copyright (c) 1992-2004, Research Systems, Inc. All rights reserved. ; Unauthorized reproduction prohibited. ;---------------------------------------------------------------------- ; ; GifReadByte ; Read a single byte out of the given file ; FUNCTION GifReadByte, unit COMPILE_OPT hidden ch = 0b READU, unit, ch RETURN, ch END ;---------------------------------------------------------------------- ;+ ; NAME: ; READ_GIF ; ; PURPOSE: ; Read the contents of a GIF format image file and return the image ; and color table vectors (if present) in the form of IDL variables. ; ; CATEGORY: ; Input/Output. ; ; CALLING SEQUENCE: ; READ_GIF, File, Image [, R, G, B] ; ; INPUTS: ; File: Scalar string giving the name of the rasterfile to read ; ; Keyword Inputs: ; CLOSE = if set, closes any open file and returns if the MULTIPLE images ; per file mode was used. This keyword is used ; without additional parameters. ; ; MULTIPLE = if set, read files containing multiple images per ; file. Each call to READ_GIF returns the next image, ; with the file remaining open between calls. The File ; parameter is ignored after the first call. Reading ; past the last image returns a scalar value of -1 in IMAGE, and ; closes the file. When reading the 2nd and subsequent ; images, R, G, and B are not returned. ; ; OUTPUTS: ; Image: The 2D byte array to contain the image. ; ; ; OPTIONAL OUTPUT PARAMETERS: ; R, G, B: The variables to contain the Red, Green, and Blue color vectors ; if the rasterfile containes colormaps. ; ; SIDE EFFECTS: ; None. ; ; COMMON BLOCKS: ; READ_GIF_COMMON. ; RESTRICTIONS: ; This routine only reads in the first image in a file (the format ; allows many). Local colormaps are not supported. ; Only 8 bit images are supported. ; ; The Graphics Interchange Format(c) is the Copyright property ; of CompuServ Incorporated. GIF(sm) is a Service Mark property of ; CompuServ Incorporated. ; ; EXAMPLE: ; To open and read the GIF image file named "foo.gif" in the current ; directory, store the image in the variable IMAGE1, and store the color ; vectors in the variables R, G, and B, enter: ; ; READ_GIF, "foo.gif", IMAGE1, R, G, B ; ; To load the new color table and display the image, enter: ; ; TVLCT, R, G, B ; TV, IMAGE1 ; ; MODIFICATION HISTORY: ; Written June 1992, JWG ; Added GIF89a and interlaced format, Jan, 1995, DMS. ; Added MULTIPLE and CLOSE, Aug, 1996. ; August, 2000 KDB ; - Fixed issues with multiple image files that contain ; images of differing sizes. ; - Cleaned up the formatting and added comments. ; - Removed junk reads used to skip data and made ; use of point_lun (save some memory cycles). ; ;- ; PRO READ_GIF, FILE, IMAGE, R, G, B, MULTIPLE=mult, CLOSE=close ;; Define GIF header (and screen descriptor. Used for Multiple) COMMON READ_GIF_COMMON, unit, scrWidth, scrHeight on_error, 2 ;Return to caller on errors if(n_elements(unit) eq 0)then $ unit = -1 image = -1 ;No image read yet ;; Error handling block closeFile: CATCH, errorIndex if keyword_set(close) OR (errorIndex NE 0) then begin CATCH,/CANCEL ; no infinite loops... if unit gt 0 then FREE_LUN, unit unit = -1 IF(errorIndex NE 0)THEN BEGIN errorMessage = !ERROR_STATE.MSG MESSAGE, errorMessage, $ NONAME=STRMID(errorMessage,0,8) EQ 'READ_GIF' ENDIF return endif ;; Main GIF Header declaration. header = { magic : bytarr(6), $ width_lo : 0b, $ width_hi : 0b, $ height_lo : 0b, $ height_hi : 0b, $ screen_info : 0b, $ background : 0b, $ reserved : 0b } ;; local image header declaration ihdr = { left_lo : 0B, $ left_hi : 0B, $ top_lo : 0B, $ top_hi : 0B, $ iwidth_lo : 0B, $ iwidth_hi : 0B, $ iheight_lo : 0B, $ iheight_hi : 0B, $ image_info : 0b } ; its content if(keyword_set(mult) and unit gt 0)then $ goto, next_image if(unit gt 0)then $ free_lun, unit OPENR, unit, file, /GET_LUN, /BLOCK READU, unit, header ;Read gif header ;; Check Magic in header: GIF87a or GIF89a. gif = STRING(header.magic[0:2]) vers = STRING(header.magic[3:5]) if( gif NE 'GIF')then $ MESSAGE, 'File ' + file + ' is not a GIF file.' if(vers ne '87a' and vers ne '89a')then $ MESSAGE, /INFO, 'Unknown GIF Version: '+vers+'. Attempting to read...' ;; Get the virtual screen width and height scrWidth = header.width_hi * 256 + header.width_lo scrHeight = header.height_hi * 256 + header.height_lo ;; Find out how big the color map is bits_per_pixel = (header.screen_info AND 'F'X) + 1 color_map_size = 2 ^ bits_per_pixel ;; Read in the colormap (optional) if((header.screen_info AND '80'X) NE 0 )then begin map = BYTARR(3,color_map_size, /NOZERO) READU, unit, map map = transpose(map) r = map[*,0] g = map[*,1] b = map[*,2] endif ;; Read the image description next_image: while( 1 )do begin ;; Read till we get a terminator cmd = GifReadByte(unit) ;; Loop thru commands in file. case string(cmd) of ';': begin ;; GIF trailer (0x3b) close = 1 GOTO, closeFile END ',': begin ;; Image description (0x2c) readu,unit,ihdr ;; Check for file formats we don't support ;; We don't support local colormaps if((ihdr.image_info AND '80'X) NE 0)then begin ;;Local color map lcolor_map_size = 2^((ihdr.image_info and 7) + 1) point_lun, (-unit), iPnt point_lun, unit, iPnt + (3*lcolor_map_size) message,'Local colormaps ignored.', /CONTINUE endif ;; Size of this image? iWidth = ihdr.iwidth_hi * 256 + ihdr.iwidth_lo iHeight = ihdr.iheight_hi * 256 + ihdr.iheight_lo ;; Allocate an array to hold the image image = BYTARR(iWidth, iHeight, /NOZERO) ;; Now call special GIF-LZW routine hidden within IDL ;; to do the ugly serial bit stream decoding DECODE_GIF,unit,image ; magic ;; This should be the 0 byte that ends the series: junk = GifReadByte(unit) ;Loop thru commands in file. if(junk ne 0)then $ message,/info,'No trailing 0.' ;; Reorder rows in an interlaced image if((ihdr.image_info AND '40'X) NE 0 )then begin l = lindgen(iHeight) ;Row indices... ;; Gif interlace ordering p = [l[where(l mod 8 eq 0)], l[where(l mod 8 eq 4)], $ l[where(l mod 4 eq 2)], l[where(l and 1)]] tmpImage = bytarr(iWidth, iHeight, /NOZERO) l = iHeight-1 for i=0, l do $ tmpImage[0, l-p[i]] = image[*,l-i] image = temporary(tmpImage) endif ;; Ok, is this image the same size as the screen size (main image)? if( iHeight ne scrHeight or iWidth ne scrWidth)then begin tmpImage = replicate(header.background, scrWidth, scrHeight) x0 = ihdr.left_hi * 256 + ihdr.left_lo y0 = scrHeight - ((ihdr.top_hi * 256 + ihdr.top_lo) + iHeight) tmpImage[x0:x0+iWidth-1, y0:y0+iHeight-1] = $ image[0:iWidth-1, 0:iHeight-1] image = temporary(tmpImage) ;; Nuc the memory endif if(keyword_set(mult)) then $ return ;Leave file open close = 1 ; otherwise close the file GOTO, closeFile end '!': BEGIN ;Gif Extention block (ignored) (0x21) label = GifReadByte(unit) ;; toss extension block label repeat begin ;; read and ignore blkss blk_size = GifReadByte(unit) ;; block size if(blk_size ne 0 )then begin point_lun, (-unit), iPnt point_lun, unit, iPnt + blk_size endif endrep until(blk_size eq 0) end ELSE: message,'Unknown GIF keyword in ' + $ file + string(cmd, format='(2x,Z2)') ENDCASE endwhile END