[Gimp-user] File size reduction

[rich <forums gimpusers com>]

> Hello,

> My name is Derek Mortimer.

> I am looking for an open source application to reduce the number of pixels, thus reducing the number of 
> kilobytes or megabytes, in a normal picture file, jpeg, etc.

> In Photoshop, the process is called downsampling.  I have looked at the documentation for GIMP and sampling 
> does not seem to be the correct term for the requisite process.  Nor can I find what is the correct term in 
> GIMP.

> Does the process of pixel reduction and file size reduction exist in GIMP, please?

> If it does, what is the technical term, please, so that I can look it up in the documentation for GIMP?

> Thank you for your help.

> All the best,

> Derek Mortimer

You would think that PS 'downscaling' is the same as Gimp rescale but I have seen one PS article that rambled 
on about having a set of 'downscaled' images for setting up a DP printed page. Once the page is set up the 
full size images were substituted, why work this way I don't know, possibly commercial printers prefer this.

So my take on the subject adds one step to resizing an image.
say original jpg image is 1500x1500 pix (file size 440 KB) resized to 500x500 pix (77 KB) if the print 
resolution (menu: Image -> Print Size) is set respectively to 300 & 100 then normally, with gimp default 
settings, the size difference is obvious. Turn off dot-for-dot (menu: view -> dot-for-dot) and the two images 
display the same.

screen shots. http://i.imgur.com/jhd16.jpg

Best algorithm for regular resizing, some say, bicubic, some sinc, it is a matter of preference.

Best compressed format for saving, obviously jpeg is lossy but it is universal and if it is the final image, 
why not.


-- 
rich (via gimpusers.com)