[digiKam-users] JPEG grows bigger. Why?

Dmitri Popov dmpop at tokyoma.de
Sat Aug 7 20:33:53 BST 2021

Hi Andrew,

Thank you very much for your detailed reply.

> But I suspect the most likely answer is that the original was saved at less than 100% quality.

Just out of curiosity, how is that possible? I mean, if the original (let's call it IMAGE A) was saved with less than 100% quality, then some information would be inevitably discarded. Logically, saving IMAGE A at 100% shouldn't result in IMAGE B that is larger than IMAGE A. Because you can't have something more out of nothing. Am I making any sense?

Kind regards,
Tōkyō Made - https://tokyoma.de/

August 6, 2021 11:42 PM, "Andrew Goodbody" <ajg02 at elfringham.co.uk> wrote:

> Jpeg is a lossy compression format. The size of the file is dependant on two things for the most
> part. The first is what is in the picture and the second is what quality it is saved at. Saving at
> 100% quality generally greatly increases the file size. So the increase may be either that you are
> saving it at a higher quality than previously. Or else the changes you make are resulting in an
> image that does not compress so well and so a larger file is produced. It may also depend on which
> code is used to implement the compression used in the jpeg image.
> So the answer is 'it depends and we cannot tell without detailed inspection of both files by
> someone who can determine what is going on'.
> But I suspect the most likely answer is that the original was saved at less than 100% quality.
> Andrew
> On 06/08/2021 21:52, Dmitri Popov wrote:
>> Hello,
>> Another day, another question from yours truly. Actually, that's something I've noticed long time
>> ago, but I never bothered to ask. Until now.
>> When I edit a JPEG file in digiKam, and then save at 100% quality, the result is usually double the
>> size of the original (for example, a ~11MB JPEG file becomes larger than 22MB). Where do the extra
>> megabytes come from?
>> Kind regards,
>> Dmitri
>> ---
>> Tōkyō Made - https://tokyoma.de

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