QUERY_PNG

QUERY_PNG is a method of obtaining information about a PNG image file without having to read the file. See QUERY_* Routines for more information.

Syntax

Return Value

This routine returns a long with the value of 1 (one) if the query was successful (and the file type was correct) or 0 (zero) on failure.

Arguments

Filename

Info

Returns an anonymous structure containing information about the image in the file. The Info.TYPE field will return the value `PNG'.

Keywords

Examples

Query included in creating RGBA (16-bit/channel) and Color Indexed
(8-bits/channel) image.

rgbdata = UINDGEN(4,320,240) 
cidata = BYTSCL(DIST(256)) 
red = indgen(256) 
green = indgen(256) 
blue = indgen(256) 
WRITE_PNG,'rgb_image.png',rgbdata 
WRITE_PNG,'ci_image.png',cidata,red,green,blue 
 
; Query and Read the data: 
names = ['rgb_image.png','ci_image.png','unknown.png'] 
 
FOR i=0,N_ELEMENTS(names)-1 DO BEGIN 
   ok = QUERY_PNG(names[i],s) 
   IF (ok) THEN BEGIN 
   HELP,s,/STRUCTURE 
   IF (s.HAS_PALETTE) THEN BEGIN 
      img = READ_PNG(names[i],rpal,gpal,bpal) 
      HELP,img,rpal,gpal,bpal 
   ENDIF ELSE BEGIN 
      img = READ_PNG(names[i]) 
      HELP,img 
   ENDELSE 
   ENDIF ELSE BEGIN 
      PRINT,names[i],' is not a PNG file' 
   ENDELSE 
ENDFOR 
END