On 2015-07-10 12:24:14 +0000, PeterN said:

I really wish someone would explain why two images with the same pixel
dimensions, and saved at the same compression level, would not be the
same size.

Actually two of us have given you an explaination. The file size of two
images cropped to identical pixel dimensions is going to be determined
by image data content which is a combination of detail area, contrast
level and color content.

For example, if those two identical dimensioned images were a sky scape
with large big color fields with little detail, and shot of a bird with
fine plumage detail, the file size for the bird might well be larger.

Given that, if you use the LR export method I have explained where the
dimensions are set and the file size limited after a crop to a specific
aspect ratio you will always be within the set export file size limit.

Here are two images cropped and sized to the same aspect ratio one is
11.9 MB the other 16.8 MB

On export, where I have set the file size limit at 1000 KB, the first
goes from 11.9 MB to 871 KB and the second goes from 16.8 MB to 836 KB.
The export dialog forced higher compresion on the larger original, but
both are now within the 1000 KB limit for the pixel dimensions I set.
They are both 2133 x 1200, or cropped to 16:9.
https://db.tt/614ommeD
https://db.tt/6buHT51P


--
Regards,

Savageduck