[Digikam-users] What am I doing wrong?

Stuart T Rogers stuart at stella-maris.org.uk
Sat Aug 30 21:00:50 BST 2014

Yes I see it now, dont know why I ignored that.... must be selective 


On 30/08/14 20:50, cerp wrote:
> I agree Stuart .... I am experiencing the same problem, and I had
> already posted the same issue in the last week.
> Regards
> Quoting Stuart T Rogers <stuart at stella-maris.org.uk>:
>> On 30/08/14 18:23, Remco Viëtor wrote:
>>> On Saturday 30 August 2014 13:04:29 George Avrunin wrote:
>>>> On Sat, 30 Aug 2014 13:40:03 +0200, Remco Viëtor wrote:
>>>>> As you manipulate the image by adding the watermark, the image will
>>> have
>>>>> to be recompressed on saving. And like was said in a similar thread, a
>>>>> PC has more power than a camera, so it might do a better job at
>>>>> compressing w/o degradation.
>>>> I don't think this is true, given how the JPEG algorithm does
>>>> compression.  It's been a long time since I looked carefully at
>>>> this, but
>>>> my recollection is that the "compression ratio" you set directly
>>>> affects
>>>> only a single step where you divide the discrete cosine transform
>>>> coefficients (for the standard 8x8 block that JPEG operates on) by the
>>>> corresponding coefficients in a quantization matrix that is
>>>> determined by
>>>> the percentage compression you specify.  It's conceivable that there's
>>>> some difference in numerical precision between what's done on a camera
>>> and
>>>> what's done on various computers, which would affect other parts of the
>>>> JPEG process, and that this would affect the reduction achieved by
>>>> the lossless run-length compression that's done afterwards, but I don't
>>>> think that having additional computing power means that compression
>>>> with
>>>> specified percentage will typically yield a smaller file.  As I
>>> understand
>>>> it, higher numerical precision might make the run-length compression
>>>> less
>>>> effective, depending on the inputs.
>>>> If I'm wrong about that, I'd be grateful if someone would straighten me
>>>> out. :-)
>>>>   George
>>> True, so that's not the cause.
>>> What Stuart might try is add a 'convert to jpeg' step in tgeh batch
>>> queue
>>> and see if that changes things (this will also allow him to play with
>>> the
>>> jpeg compression paramters).
>>> _______________________________________________
>>> Digikam-users mailing list
>>> Digikam-users at kde.org
>>> https://mail.kde.org/mailman/listinfo/digikam-users
>> Well I did just that (connvert to jpeg first and watermark second) and
>> guess what .... the file ended up at 1.7MB with 100% set for the jpeg
>> option.
>> However I tried it again doing the watermark FIRST and the convert to
>> jpeg second and this time I get a file of 6.5MB the same as GIMP.
>> So it looks like the batch watermark option seems to be at fault.
>> Equally it makes no sense to convert a jpeg to a jpeg.
>> There HAS to be a bug here somewhere....
>> Stuart
>> --
>> Website: http://www.stella-maris.org.uk
>> or:      http://www.broadstairs.org
>> _______________________________________________
>> Digikam-users mailing list
>> Digikam-users at kde.org
>> https://mail.kde.org/mailman/listinfo/digikam-users
> _______________________________________________
> Digikam-users mailing list
> Digikam-users at kde.org
> https://mail.kde.org/mailman/listinfo/digikam-users

Website: http://www.stella-maris.org.uk
or:      http://www.broadstairs.org

More information about the Digikam-users mailing list