; eseguire nella cartella con le immagini da trattare:
;
; gimp -i -b '(batch-format-convert "*.jpg" ".png")' -b '(gimp-quit 0)'
; 
; input:  *.jpg *.gif *.tiff *.png *.xcf
; output: .jpg .gif .tiff .png 
;


(define (batch-format-convert pattern-in format-out)

  (let* 
	(
		(filelist (cadr (file-glob pattern-in 1)))
		(fmt-out format-out)
	)
    
	(while 
		(not (null? filelist))

           	(let* 
			(
				(filename (car filelist))
                  		(image (car (gimp-file-load RUN-NONINTERACTIVE filename filename)))
                  		(drawable (car (gimp-image-flatten image)))
			)
				
			(if (and (equal? fmt-out ".gif") 
				 (not (= (car(gimp-drawable-type drawable)) INDEXED-IMAGE) )
			    )
				(gimp-convert-indexed image FS-DITHER MAKE-PALETTE 256 FALSE TRUE "aaa")
			)
		

			(if (and (equal? fmt-out ".jpg") 
				 (not (= (car(gimp-drawable-type drawable)) RGB-IMAGE) )
			    )
				(gimp-convert-rgb image)
			)

			(set! filename 
				(string-append 
					(substring filename 0 
						(- (string-length filename) 
						   (- (string-length pattern-in) 1) 
						)
					) 
					"_out"
					fmt-out
				)
			)

             		(gimp-file-save RUN-NONINTERACTIVE image drawable filename filename)

             		(gimp-image-delete image)

		)

  		(set! filelist (cdr filelist))
	)

   )

)