[digiKam-users] why is batch convert to bw so extremely slow?

[Daniel Bauer]

Am 01.07.20 um 07:42 schrieb Maik Qualmann:
> Saving large PNG files takes so long, Gimp is not faster either. Are you sure
> you saved it as a PNG in the editor and not as a JPG? If versioning is active,
> "Save changes" creates a JPG depending on the setting, which is very fast. If
> you want to have a JPG in BQM, you have to attach the tool for saving in JPG
> at the end of the tools.
> 
> Maik

I use to work with png. The difference I see is between the batch tool 
and the edit tool. Of course, saving "save as png" takes a bit, but 
compared to the batch tool it is extremely much faster.

There is no versioning active. It reads the original png, converts to 
bw, then saves in a subfolder as png. This takes 2 to 3 minutes per 
image, which is really long.

Doing the same manually, also in digikam: in album click on image to 
open editor, color: convert to bw, save as png... is at least ten times 
faster, but needs a lot of clicks and is very boring - and ideal job for 
a batch process. But I had to do it manually because I didn't want to 
wait almost 3 hours...

I know that highly compressed png take more time, but in settings I have 
set png compression to 5, and I think, the batch process uses that 
compression, too. Or not?

> 
> Am Dienstag, 30. Juni 2020, 20:11:56 CEST schrieb Daniel Bauer:
>> Hi,
>>
>> Sometimes I'd like to convert a complete album to bw. I added 69 color
>> png of 30-40MB to a batch, selected convert to bw, save in new folder, run.
>>
>> Each image takes more tan 2 minutes to convert. When I open it in
>> editor, and click color->bw it works immediately, also saving the file
>> is fast. But batch processing is so slow that it cannot be used.
>>
>> Now I must go through the album in editor, click color->bw->save->next
>> 68 times, which is not comfortable but at least 10 times faster :-(
>>
>> Why?
> 
> 
> 
> 

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