[digiKam-users] More on changing image resolution

[Northern Colorado Event Photograph]

Yes, I understand that ". . . a digital image doesn't have an intrinsic size in inches, only a size in pixels."

And I also understand that "Resolution plays a role when printing . . . ."

But that is my point.

Suppose you are processing (for example) a low res JPG image out of a smart phone,  And you have a request for a print (4 x 6 or 5 x 7).

To provide a satisfactory print, it may make sense to increase the resolution of this image.  Yes, I understand that this is not usually a good idea and can potentially result in a number of issues with the final product.

Nevertheless, it is worth a try, if for no other reason that to make the requestor (customer/client) happy.

Now 300 ppi doesn't make sense in this case, but 120 or 150 might.

Unfortunately, if I correctly understand the messages in this thread, there is no way in digiKam to make this change independent of changing the dimensions (resizing) of the image.

BTW, FWIW, here a number of links to articles that can help both amateurs and professionals obtain a better understanding of this topic:

Rediscover - Understanding Resolution - Luminous Landscape
https://luminous-landscape.com/rediscover-understanding-resolution/

Res-Demyst - Luminous Landscape
https://luminous-landscape.com/res-demyst/

The Truth About Resolution - CreativePro.com
https://creativepro.com/the-truth-about-resolution/

Understanding Resolution - Luminous Landscape
https://luminous-landscape.com/understanding-resolution/

ShortCourses-Pixels per Inch
http://www.shortcourses.com/sensors/sensors1-15.html

Peachpit: Creating and Managing Images > Changing Image Size and Resolution
http://www.peachpit.com/articles/article.aspx?p=705532&seqNum=3&rl=1

[leoutation]

On 8/24/19 10:35 PM, Northern Colorado Event Photograph wrote:
>
> Unfortunately, if I correctly understand the messages in this thread,
> there is no way in digiKam to make this change independent of changing
> the dimensions (resizing) of the image.

Fortunately for this kind of work, Gimp exists :)


--
Greetings

Maderios

Le 24/08/2019 à 22:35, Northern Colorado Event Photograph a écrit :

> Suppose you are processing (for example) a low res JPG image out of a
> smart phone,  And you have a request for a print (4 x 6 or 5 x 7).
>
> To provide a satisfactory print, it may make sense to increase the
> resolution of this image.

no

your printer driver should give you the option of choosing the image size

jdd

--
http://dodin.org

[digikam-2]

This is why there is imagemagick: https://www.imagemagick.org/

to resize: convert -size 1980x1020 infile.jpg outfile.jpg
to compress: convert -quality 65 infile.jpg outfile.jpg

and you can combine them...

http://www.imagemagick.org/Usage/resize

What I wish is somebody provides an "execute command" after
processing of the image.

I do this manually because the resize of DT is "mushy", so I export
full size and resize/shrink + sharpen in IM. (btw the parameter are
executed in the order of the command line)


On Sat, 24 Aug 2019 14:35:52 -0600
Northern Colorado Event Photograph <[hidden email]>
wrote:

> Yes, I understand that ". . . a digital image doesn't have an
> intrinsic size in inches, only a size in pixels."
>
> And I also understand that "Resolution plays a role when
> printing . . . ."
>
> But that is my point.
>
> Suppose you are processing (for example) a low res JPG image out of
> a smart phone,  And you have a request for a print (4 x 6 or 5 x 7).
>
> To provide a satisfactory print, it may make sense to increase the
> resolution of this image.  Yes, I understand that this is not
> usually a good idea and can potentially result in a number of
> issues with the final product.
>
> Nevertheless, it is worth a try, if for no other reason that to
> make the requestor (customer/client) happy.
>
> Now 300 ppi doesn't make sense in this case, but 120 or 150 might.
>
> Unfortunately, if I correctly understand the messages in this
> thread, there is no way in digiKam to make this change independent
> of changing the dimensions (resizing) of the image.
>
> BTW, FWIW, here a number of links to articles that can help both
> amateurs and professionals obtain a better understanding of this
> topic:
>
> Rediscover - Understanding Resolution - Luminous Landscape
> https://luminous-landscape.com/rediscover-understanding-resolution/
>
> Res-Demyst - Luminous Landscape
> https://luminous-landscape.com/res-demyst/
>
> The Truth About Resolution - CreativePro.com
> https://creativepro.com/the-truth-about-resolution/
>
> Understanding Resolution - Luminous Landscape
> https://luminous-landscape.com/understanding-resolution/
>
> ShortCourses-Pixels per Inch
> http://www.shortcourses.com/sensors/sensors1-15.html
>
> Peachpit: Creating and Managing Images > Changing Image Size and
> Resolution
> http://www.peachpit.com/articles/article.aspx?p=705532&seqNum=3&rl=1

--
sknahT

vyS

[Daniel Bauer-2]

Am 24.08.19 um 22:35 schrieb Northern Colorado Event Photograph:

> Yes, I understand that ". . . a digital image doesn't have an intrinsic
> size in inches, only a size in pixels."
>
> And I also understand that "Resolution plays a role when printing . . . ."
>
> But that is my point.
>
> Suppose you are processing (for example) a low res JPG image out of a
> smart phone,  And you have a request for a print (4 x 6 or 5 x 7).
>
> To provide a satisfactory print, it may make sense to increase the
> resolution of this image.  Yes, I understand that this is not usually a
> good idea and can potentially result in a number of issues with the
> final product.

If you increase the resolution of an image (that is pixels per inch or
cm) then logically the image size (in inch or cm) gets smaller /when
printed/.

So if you have an image with 1000 pixels width and you set the
resolution to 100 pixels per inch, your image prints 10 inches wide.
If you set the resolution to 200 pixels/inch it prints 5 inches wide;
500 pixels/inch = 2 inches, 10pixels/inch = 100 inches).

With all those changes in resolution actually nothing is changed in the
image. All the pixels stay the same. The only thing that changes, is
"how many pixels the printer takes to fill one inch". But you achieve
exactly the same when you simply put the print size in the print dialog
(the printer or its driver will simply divide the pixels that are
available in the image by the width or height you entered).

So in the above example with your 1000px wide image (lets say its saved
with resolution of 70 px/inch) and you enter 10inches wide in the
printer dialog, it will be printed with a resolution of 100 pixels/inch.
If you enter 5 inches width, it prints with a resolution of 200 px/inch.
It doesn't have any influence what resolution is saved in the image.

Also if you go to a print-lab with your file you just say: print it at
this or that size. You don't have to care about the resolution.

The same happens when you paste the image in a print publishing software
(for example adobe's pdf crating software). Here indeed you give a
resolution and print size for the document, because it is aimed for
printing in a defined size. When you paste the image file it will be
pasted in the "cm-size" according to your document-resolution setting
and the available pixels in your image file. (you can then drag it
smaller and the software will actually change the image size, cut away
from the original pixels. You can drag it larger and the software will
fill the missing pixels with "invented" ones or lower the resolution,
depending on your settings).

The only thing you have to care is that you have enough pixels in your
image to achieve a good print quality in the desired size.

Now, if you have that 1000px wide image and want it to print 10 inches
wide with a resolution of 200 px/inch, there are not enough pixels in
your image. You'd need 2000 pixels width. Theoretically you can enlarge
your image (in Gimp for example). This will add new pixels. Those new
pixels are calculated and are not from the original image. In most cases
it will give a bit a blurred result.

Most printers can soften the otherwise visible pixels when there is not
enough resolution, and that mostly gives better results than adding
pixels in Gimp or photoshop. I just printed a 2.5m (98.42") poster from
a file with 5110 pixels which means a resolution of 52 pixels/inch only
and there are absolutely no pixels visible. Of course it's not a 100%
sharp when looked at from close, but from 1m distance the result is perfect.

> Nevertheless, it is worth a try, if for no other reason that to make the
> requestor (customer/client) happy.

The client will be happy if there are enough pixels to reach the quality
in print he wants. You don't have to care about the resolution
information that is saved in the file.

> Now 300 ppi doesn't make sense in this case, but 120 or 150 might.
>
> Unfortunately, if I correctly understand the messages in this thread,
> there is no way in digiKam to make this change independent of changing
> the dimensions (resizing) of the image.

Digikam can only change the pixel-size of an image.

The only moment when you really want to change the resolution is when
you must deliver an image in a given print size in a given resolution
(e.g. A4 in 250 dpi). Then you must use the Gimp.

I had such cases and still simply delivered the image in 72dpi but with
the exact amount of pixels that would fill A4 at 250 dpi. The client
didn't even notice it, because an image file of 2067 pixels with and
72dpi will print exactly 21cm wide when the printer is set to 250dpi, or
will print exactly at 250dpi when the printer is set to 21cm width.

So, in general: forget about changing resolution in images unless you
deliver to a print shop that doesn't know how his printer works  :-)



--
Daniel Bauer photographer Basel Málaga
https://www.patreon.com/danielbauer
https://www.daniel-bauer.com