Changing resolution / DPI in BQM

[Laurent Espitallier]

Le 05/10/2025 à 13:00, digikam-users-request at kde.org a écrit :

> Date: Sun, 05 Oct 2025 09:43:53 +0200
> From: Remco Viëtor<remco.vietor at wanadoo.fr>
> To:digikam-users at kde.org
> Subject: Re: Changing resolution / DPI in BQM
> Message-ID: <31192391.1r3eYUQgxm at manticore>
> Content-Type: text/plain; charset="utf-8"
>
> On dimanche 5 octobre 2025 09:19:39 heure d’été d’Europe centrale Laurent
> Espitallier wrote:
>> Hi everyone!
>>
>> I don't think I've seen a way to change the DPI of an image in the batch
>> queue manager, nor in the G'MIC filters. Have I missed something? If
>> not, do you think it would be easy to implement?
>>
>> Changing the DPI is possible in the image editor.
>>
>> Laurent
> "DPI" just doesn't make sense for an image file, as it doesn't have a physical
> dimension. Strictly speaking, you can't even define a "DPI" for an image file
> (many programs trying to do it anyway doesn't change that).
>
> DPI only makes sense when printing to a physical support, e.g. paper, and then
> you are dealing with three directly coupled values:
> - size in pixels;
> - size in inches/cm:
> - DPI, which is  (size in pixels)/(size in inch), and can be different for
> each direction (hor or vert)...
> And even there, DPI is mostly useful to see if you have enough pixels for
> decent quality (and the optimal DPI depends on the print size: larger prints
> need less DPI).
>
> DPI also makes sense for a printer, as in "I can put so many pixels in an
> inch". To complicate the issue even further, printers can also specify how
> many dots of ink they can put in an inch. But as they often need to put
> several dots per pixel...
>
> TL,DR: DPI is only useful when printing to verify if you reach the required
> quality level.
>
Yet some users find it useful and easier in their workflow to resize 
image by changing dpi (in order to display images to screen, e.g. 300 > 
72 dpi) rather than specifying a number of pixels.

That was implemented in XnView a few years ago 
https://newsgroup.xnview.com/viewtopic.php?t=43382

Laurent
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