Adjusting Exposure VS Brightness

[moondog]

When working with NEF's, how is the best way to decide when to expose more or just brighten up?

Now, here is why I ask: I almost always work from the NEF's, and I usually first off click the "Auto" button to see what the editor wants to do, then make changes according to my preference. The auto usually up's the exposure and I usually tone it back down to what I think looks good. Here lately, I started bringing the exposure back down to zero and using the brightness to control that part of the output. I can't see much difference in having the exposure up and brightness down verses exposure down (or "as shot") and brightness up. Is there? What should I look for besides of course the over and under exposure indicators. Before I make a total tail of myself, I should say that I would see the difference once it's overexposed at the point of washing out, but I'm talking about the smaller adjustments of controlling the brightness. I'm using PSE 7. Any help would be appreciated.

[BobF]

The difference is that Exposure impacts the entire image equally. Brightness works on the midtones. Increasing Brightness will lighten mids and compress those values against highlight values. Reducing brightness will darken mids and compress those values against shadow values. Exposure is a linear adjustment and won't impact overall image contrast provided that pixels aren't increased to the point of overexposure or shadows aren't reduced to the point of full black. Pushing Brightness too far will begin to impact highlights as well.

Exposure will stop working on highlight areas once those values are at the point of full exposure. At that point, you begin to compress mid and darker values relative to highlights and reduce overall contrast. The opposite is true for shadows.

Brightness can be considered a form of gamma adjustment.

[moondog]

Great explanation... Do I understand correctly that "compress those values against highlight values" would mean that it darkens those areas next to the areas being lightened?

[BobF]

No. It reduces the separation in brightness by making the mids brighter while leaving the highlights mostly untouched.

[WRon]

Bob, as usual, is right on the money.

The only thing I'd add is that monitors are often set too bright for photographic work. Thus, if a monitor is too bright, then one's tendency is to darken the image by lowering its brightness. If one is viewing his or her images only on his or her own computer, then adjusting the image to suit one's monitor is fine. However, if one wishes to share images or make prints of them, then the images may be too dark on someone else's monitor and they may be too dark when printed.

Just thought I'd share this observation.

[moondog]

I knew I could count on this forum to provide accurate information and I appreciate it. I may not completely follow the "compress those values against shadow values" and “reduces the separation in brightness" lingo, but that is ok because my question was answered and I can apply it to my photos. Perhaps I can research compressing values and reducing separation before stepping back in... I’m certain it will be a bonus. Again, thanks!

[drh681]

think in terms of frequency modulation.

[BobF]

OK, here's a quick example. You see the first image below has nice separation between all the shades of grey?



You can't see it because this site has a white background but there's a white block at the right end as well.

Now, when I move the Brightness slider all the way up to 150 you see what happens.



You've got a compression of the brighter tones from the middle of the blocks to the right (bright) end but the shadow blocks are left unchanged. That's a compression of brightness values.

Now with a move to -150 on the Brightness slider you get the following.



You've got a compression at the left, dark end of the scale and a reduction in separation of discrete grey tones.

[BobF]

That should have been 'shadow block is...' Editing on this site really blows.

[moondog]

I really appreciate the example because it helps to understand the terminology usage, and I'm sure I wasn't the only one viewing that could use the schooling. Do you have any suggestions for mid level training (preferably on-line) material? I don't need a step by step how to adjust exposure, or step by step anything, but more in dept details about how it all works, and terminology usage would benefit me more than anything else at this stage.