cropping/resizing: quality?

Hi,

I have cropped a very tiny bit from the left and upper sides of a picture, 
and the new filesize of the picture was less then 1/5 of the previous 
size. The original picture was taken by a Nikon D90, with smallest jpg 
compression. I guess gwenview overrides the compression level, or 
something similar, leading finally to quality loss.

The same holds for resizing: when resizing the original 4288x2848 picture 
by 'convert' to 4000x2657, the filesize decreases to about 1/2. When 
making the same resizing with gwenview, the file size decreases to less 
than 1/6 of the original filesize.

Is there any way to control the quality of these transformations? It would 
make sense to keep the same quality as the original picture, by default.

Thanks


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