Carusoswi <forums <at>> writes:

> So, I have used Gimp to downsize large architectural drawing images from
Tiff's to jpgs.  

Let's be precise. You are not "downsizing" the images. "Downsize" means
making a picture physically smaller, as in, having less pixels. According
to your own description, you are not doing this. What you are doing is saving
the file in another format which has better compression.

> Today, the source tiff which is 900 mb in size is being converted to jpg
> which is 6 or 7 mb in size, totally unusable. 
> Additionally, if I simply open the source in Gimp, save it to another 
> directory from Gimp without making any changes, the file also grows to 
> 6 or 7 mb.

Now I'm completely confused. You say the original is 900MB. then you say it
"grows" to 6-7MB. But 900 is much larger than 6 or 7! Please explain.
Did you by any chance mean 900KB and not MB? that would explain it.

> What I really cannot understand is why Gimp is causing unaltered files to 
> grow in size when saving them.  Is that normal?

The TIFF format has many options, including several compression modes, and 
also an uncompressed mode. So, assuming you meant 900KB:
You probably opened a compressed TIFF, and then when you saved the file, 
GIMP saved it as an uncompressed one. If the file has a lot of empty space
 - as in, a large empty area of white (or other) color - it will compress 
dramatically. When you re-save the TIFF, a dialog should open after you 
set the file name and folder. Choose "LZW" instead of "none" and see if that
solves the TIFF re-saving issue.

Also, because of the differences in compression types, some images that 
compress very well in TIFF's type of compression, compress very badly in 
JPG-type compression. The type of images that do this are images which have
lots of very thin lines, in other words: blueprints. I don't have a good
solution for saving this type of file in JPG. It really depends on why you
want to re-save the file to JPG in the first place.

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