JPEG Batch Output - Image Sizing & Quality

[Lamar]

After a couple of month of amateur use, I'm stuggling with having a solid understanding of the Quality value & Image Sizing setting in JPEG Batch Output.

1. If the Quality value is reduced from 100 to 80%, what specifically is being reduced? My tests of a full size RAW file from my Canon 60D (5184x3456) processed at 80% are still 5184x3456 @ 300 dpi. But the file size is smaller. What was removed?

2. I have been looking for a "lock aspect ratio" selection for the resize choice in Image Sizing. Am I overlooking it or am I missing the way to handle this need without making a manual calculation and entering both values? Maybe my approach to this is all wrong.

3. The manual indicates "Long/Short resizing lets you specify a non-square bounding box that the output image will be fit into, regardless of the landscape/portrait formatting of the image." I'm humbled by my lack of understanding of what this means seemingly simple statement means. When would I use "Long/Short" over "Width/Height"?

In general, ASP is a great tool. I can't image having to go back to Digital Photo Professional. I just can't quite get this part figured out. Thanks in advance.

Lamar

[afx]

1. If the Quality value is reduced from 100 to 80%, what specifically is being reduced? My tests of a full size RAW file from my Canon 60D (5184x3456) processed at 80% are still 5184x3456 @ 300 dpi. But the file size is smaller. What was removed?

Details.
Google for JPG compression...
(and ignore the silly, meaningless DPI value).
If you pixel peep you might see differences. Try 50% vs 90%.
In general, for downscaled images, use 85% ore more. There is a quality jump at that value.

2. I have been looking for a "lock aspect ratio" selection for the resize choice in Image Sizing. Am I overlooking it or am I missing the way to handle this need without making a manual calculation and entering both values? Maybe my approach to this is all wrong.

Just enter the same (longest) value in Long/Short.

When would I use "Long/Short" over "Width/Height"?

Never.
At least I never found a reason to do so in the last 6 years.

cheers
afx

[Lamar]

1. I read up on JPEG Compression... that helped a lot.
2. Tested putting same longest side value in both field... that worked... wouldn't have expected it to, but that makes it easy.
3. Based on #2, I guess I never will either.

Thanks for the assistance.

Lamar