Thread: thumbnail sizes
View Single Post
  #19  
Old January 8th 18, 03:59 AM posted to rec.photo.digital
Carlos E.R.
external usenet poster
 
Posts: 278
Default thumbnail sizes

On 2018-01-08 03:17, Savageduck wrote:
On Jan 7, 2018, Carlos E.R. wrote
(in article ):

On 2018-01-07 22:22, Savageduck wrote:
On Jan 7, 2018, Phillip Helbig (undress to reply wrote
(in article ):

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

Why?
Why not use decent software?


"convert" is very decent and powerful software.
What would you use in a script, then?


Why use “convert” which I have never heard of when I have Lightroom,
Bridge, and a few others in my photgraphic tool box?


Because it is a tool designed for scripts and other repetitive tasks.
Most Linux users doing image handling will be familiar with it, but you
also have it in Windows, and is used by other tools in the back without
telling you.

https://en.wikipedia.org/wiki/ImageMagick


The tiny code excerpt from the OP would process an entire directory in
one click. Or one "enter". As you can see in the documentation,
"convert" has dozens of possible options, several pages:

http://imagemagick.org/script/convert.php

There are also many examples of use. For instance, there is one
"-thumbnail":

https://www.imagemagick.org/Usage/resize/#thumbnail


A whole chapter of it:

https://www.imagemagick.org/Usage/thumbnails/


And it has some information that may explain what is happening to the OP:

«Many images from digital cameras, scanning software, and some paint
programs (photoshop is notorious for this), save extra information about
the image in the form of profiles. This includes image formats such a
JPEG, PNG, TIFF and as of IM v6.2.4-1 GIF. Of course the IM specific
format, MIFF also does this. (See Image Profiles for more detailed
information).»

«These profiles can be up to 60 Kb in size, so can make a big difference
to your file size, and by default IM will preserve this profile
information. Thumbnails have no need for this data and often not even
the main image needs it.»


--
Cheers, Carlos.