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  #17  
Old January 8th 18, 02:57 AM posted to rec.photo.digital
Carlos E.R.
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Posts: 278
Default thumbnail sizes

On 2018-01-07 23:30, Mayayana wrote:
"Phillip Helbig (undress to reply)" wrote

| I've been using this to make thumbnails of jpeg files:
|
| for img in *.JPG; do
| echo thumbnailing $img
| convert -geometry 105x70 $img $img
| done
|
| Files from the K10D result in thumbnails of about 57 kB and those from
| the GR of about 46 kB, with little variation. Is there a simple
| explanation as to why?
|
| The K10D is 10 megapixels and the GR 16, but I don't see why that is
| relevant here, but maybe I am missing something.
|

Are the originals the same aspect ratio?
If not then you might be getting something
like a 105x65 and a 105x50. You also didn't
spec the compression level with the quality
parameter. (Assuming you're using ImageMagick
as Carlos speculated.)


Oh, I'm more than 95% certain :-)


You didn't say what the context of the code
is. You didn't say why you're making thumbnails
or whether they need to be the same size.


I rather suppose he is curious about why they are not about the same
size, if the pixel number is the same.

But it does not matter to me why is he making them. Not my business :-)

You
didn't extract them, which would probably make
more sense. So all we know is that you're making
thumbnails with a poorly suited tool and you don't


It is a perfectly suited tool for this task (a repeated task in a script).

much care about the quality of them. But you
do care about the file size? Why?


Then use the -quality parameter, to make sure it is the same on all
runs. With no value given, the program tries to estimate the value used
in the original and use the same (see
http://www.imagemagick.org/script/co...s.php#quality).

It'd be easier for people to provide a helpful
answer if you'd explain yourself. We're not your
mother.


Sigh... Maybe he doesn't know what other information to provide, and
you can simply politely ask for what you think you need :-)


--
Cheers, Carlos.
 




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