Re: [Gimp-user] Image transformation batch processing

[Jay Smith <jay JaySmith com>]

On 05/10/2015 11:45 PM, lloyd_borrett wrote:
> G'day,
>
> I have many directories of images, totaling more than 5000 images in total.
> Each image might be in a jpg, gif or png file format.
> I want to change all images to have a 1:1 aspect ratio, on a white background.
> I want no image to exceed 1000 x 1000 pixels at 72 dpi.
> Images already within the 1000x1000 limit should be extended to have a 1:1
> aspect ratio, as required.
> At no point is any image scaled upwards in size.
> All images should be saved in a suitably compressed way for displaying on web
> sites.
> The new images should be written into a sub-directory, with the original images
> being left in place and unchanged.
> Would like to do this as a single batch process, if needs be per directory.
>
> Here are some examples as to what should happen:
>
> 1200x1200: Image re-sized to 1000x1000. Save compressed.
>
> 1600x1200: Image re-sized to 1000x750. Then extended to 1000x1000, centred on a
> white background. Save compressed.
>
> 1200x1600: Image re-sized to 750x1000. Then extended to 1000x1000, centred on a
> white background. Save compressed.
>
> 750x750: Save compressed.
>
> 800x600: Image extended to 800x800, centred on a white background. Save
> compressed.
>
> 600x800: Image extended to 800x800, centred on a white background. Save
> compressed.
>
> Is it possible to achieve the above using Gimp?
>
> If so, how?
>
> If not, can you please recommend a image processing tool that can do this?
>
> Best regards, Lloyd Borrett.

Though we have not done some of the specific tasks or had some of the 
specific limitations/operations you describe, we have done operations 
fairly similar to this that require a lot of complex if-then-else logic. 
 To accomplish this, we used Perl and Imagemagick -- this was a few 
years ago, but I think there is/was a Perl image processing module to 
aid in such situations.

I don't recall all the details and I can't help with code samples. 
However, the good news is that the input was in the tens of thousands of 
images and the output was 4x the input (there were four output streams, 
not just one as you need, because our output had in four size ranges, 
not just your one range).  While the code took a bit of work to develop, 
the actual running (and re-running because there were always new or 
modified inputs that had to be detected/compared as new and thus new 
output created), was surprisingly fast.  Obviously the bigger the 
machine (I think we were running on a machine 16 cores and 16 GB of 
RAM), the faster the results.

One or two tiny suggestions.  You describe that the output needs to be 
centered on a white background (if the output is less than 1000 in a 
particular dimension).  The "white background" should be a command line 
parameter type of setting so that you don't have to dig into the code to 
change background color that for a particular run.  You may also want to 
consider the potential use of transparent background (if supported by 
file type of the image type being used for the output) and do the "color 
of background" on the display side (if possible) rather than in the 
image -- that would give you greater flexibility; then you might just 
need a one-line CSS change for your entire website rather than 
regenerating umpteen images.

Jay