[Digikam-users] jpg to png conversion

[Andrew Goodbody]

On 13/01/12 08:31, Dr. Martin Senftleben wrote:
> This gigantic file size never came to my attention. I had transformed
> jpgs to png, which caused a size increase of more than 10 times. Wow!
> And when I reduce this png, they become about 15 MB in size, while the
> originals are 5-6 MB. Very strange, but I guess not. I probably will
> never understand the mechanics behind this, even though I know that it
> has to do with colour tables or so.

I have to ask why you converted jpg files to png?

jpg is a lossy format which means that some image information is simply 
not preserved in the file, it has been lost. When a jpg file is used to 
recreate an image the lost information cannot be recreated exactly, it 
is replaced with something that will hopefully look about right. png is 
a lossless format so no information is lost in the file, images can be 
recreated exactly. However converting jpg to png simply locks in place 
and preserves the recreated image complete with the replacement 
information that is only an imitation of the original. It cannot ever 
exactly recreate the original image information as that was lost when 
the jpg was created.
The lossy compression used by jpg allows it to create a smaller file 
size in comparison to png which is lossless ie png simply stores more 
data and so is bigger.

Andrew