[Digikam-users] Re: need advice re: format conversion

[gerlos]

Il giorno 25/gen/2011, alle ore 14.28, Elle Stone ha scritto:
> A little experiment:
> Original jpeg: 37 KB (its an extracted preview, not a camera-generated jpeg)
> Some file size comparisons, all files saved with digikam starting with
> the original jpeg
> Saved as lossless PGF: 265 KB (7 times bigger)
> Saved as png highest quality: 251 KB
> Saved as tif: 943 KB

Maybe your experiment is not realistic, I suppose because the start image was too small.

Here's my results on a 18 Mpx JPG image, generated by my Canon SLR at maximum quality ("L"):
IMG_5565.JPG:  5,9M (original image)
IMG_5565.tif:     51M  (uncompressed data)
IMG_5565.jp2:  15M  (Jpeg-2000, a little more than twice the size)
IMG_5565.pgf:  16M  (a little more than Jpeg-2000)
IMG_5565.png: 18M  (PNG slightly bigger than previous one, and 3 times bigger than original)
IMG_5565.tif:     18M  (compressed TIFF, same as PNG)

When converting the same image to 16 bits:
IMG_5565.tif:   102M  (uncompressed data)
IMG_5565.pgf:   68M  (a little more than Jpeg-2000)
IMG_5565.png:  82M  (PNG slightly bigger than previous one, and 3 times bigger than original)

It seems that size advantages of lossless PGF over PNG are more relevant with bigger files.
Hope these figures are useful.

regards
gerlos

--
"Fairy tales are more than true, not because they tell us that dragons exist, 
but because they tell us that dragons can be beaten."
					G. K. Chesterton
       <http://gerlos.altervista.org>
gerlos +- - - > gnu/linux registred user #311588