(define (img-recode
          srcfile
          destfile
          fmt
          ckey)        

(let*
   (
    (image (car (file-img-load RUN-NONINTERACTIVE srcfile srcfile)))
    (drawable (car (gimp-image-get-active-layer image)))
   )

    (file-img-save RUN-NONINTERACTIVE image drawable destfile destfile fmt ckey)
)
)

(img-recode "samples/rgb.img" "samples/recoded-rgb565.img" "RGB565" "no")
(img-recode "samples/rgb.img" "samples/recoded-rgba.img" "RGBA" "0x0F0")

(gimp-quit 0)