Why is the 'Straighten' tool so crude?

I've always noticed it, but never more so than with iPhoto '11 which is the version I'm using (9.2.3)

I work with JPEGs, mostly from my camera ranging from 1MB to 6MB.

I just tried with a new iPhoto library in a different user account and it was the same there. (Which rules out the plist or something in the library itself.)

I'm surprised you can't see it? Try one of your photos full screen that has crisp lines in, and then use the Straighten tool while looking at the crisp details. But if you're using a later iPhoto in one of the Lions they may have fixed it?

Perhaps you're neither of you as critical as I am? By 'softening' I mean something a photographer would notice straight away, but not necessarily your average user..

(Sorry, that sounds a bit insulting - I just mean that the kind of softening I'm acutely aware of, might not be so evident to many other people?)

Incidentally, I noticed this on iPhoto '06 and iPhoto '08 too, but as that was on a G5 iMac it wouldn't be nearly so noticeable as on the later higher resolution screens. So it's not my imagination or an effect limited to one version of iPhoto on one computer. It's worth mentioning that I've never noticed this effect in Photoshop. Perhaps tomorrow I will try to demonstrate the effect with a Before and After picture to prove I'm not talking nonsense.)

This topic continues the discussion, but includes a picture to demonstrate the effect:

https://discussions.apple.com/thread/5309669

This is what I got with your image:

1. Unstraightened

2. Minimum straighten (0.6º)

This screenshot was taken immediately after clicking "Done", but before clicking the navigation arrow to save the edit and move to the next image. If you expand both you should see the softening.

This is weird! What on earth is happening? And it has ALWAYS happened in iPhoto - what you see in the screenshot is not an effect just of iPhoto '11 on a Core i5 iMac.

This is how I edit in iPhoto (in case this gives you any insight) :

1. Right-click on an image and choose 'Edit in iPhoto' (if I'm not using Photoshop)
2. Make the changes either in full screen or not
3. Click iPhoto's right arrow to save the edit(s) and move onto the next image
4. Continue through until I've done, then click the Edit button to come out of Edit

Would you do me a favour - replicate my method? Go back into a similar image with lots of reference points, straighten by only a fraction while watching the image like a hawk - do you see it soften on the first movement of the slider?