[Digikam-users] jpg to png conversion

[Dr. Martin Senftleben]

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Hi,

Am 13.01.2012 10:25, schrieb 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?

I'm not sure if that's a rhetorical question. Anyway, I was doing some
changes on the images, and didn't want to lose more info due to the
jpg-compression.
I think of it this way (maybe I'm wrong): every time I change a jpg
image, some info of the origional gets lost and the image cannot ever
be put in the original state by just reverting the changes, because it
drops the original info and adds in some new based on the changes.
But (that's what I think) when I change a png image, I can get the
original state back by reverting the changes.
I knew that png makes the files bigger, but I still do not understand
how the jpg can become 10 times bigger by converting it to png. Even
the raw images of the same picture are less than half the size of the
png file.
I'll probably never fully understand the mysteries behind this,
because I can't even see the difference. I'll probably stick to jpg
even though some information is not stored in the file. Why don't
camera manufacturers use a non-lossy format that produces smaller
images than the raw images? Or isn't that possible at all?

Regards

Martin
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