A Quick Review of Exposure and Levels Adjustments

by Ellen Anon

Recently someone was asking if it mattered whether you use the Exposure control or Levels or both to adjust an image and whether there was any difference in the results. So this week I’m going to review some basic adjustment information.

The fact is that although you can set the white point using the Exposure slider or Levels, the results you obtain will be slightly different. Let’s look at a low contrast abstract image of color reflecting in a river. Here’s the original image.
NewHampshireVG9N9198 - Version 4.jpg original.jpg

You can see on the histogram that the image is very low contrast since the pixels are bunched together. Additionally there’s a gap to the right of the data on the histogram indicating that the image isn’t using the lightest 20% of tonalities. There's also a large gap to the left indicating it isn't using roughly the darkest 40% of the tonal range.

If you first adjust the Exposure slider to try to use most of the lightest tonalities, and then use Levels to set the black point, you end up with this image. (I’m not going to adjust the middle slider or the quarter tone controls for this comparison.)
NewHampshireVersion 3.jpg Levels and Exposure.jpg


2007-11-14 04:11:28
Yes ! At last an article that talk about the digital darkroom and not the workflow !
An article about the tint inside the exposure tab would be great too!

Tx again

2007-11-14 06:14:22
Here! Here! Thanks Ellen for the suggestions. I've always felt I could do more without falling back to Photoshop...never liked round-tripping :) I second an article on those tints and a way to confirm lightest and darkest parts of an image more easily than checking numbers.

Thanks. Steve.

Ellen Anon
2007-11-14 07:38:38
I'm glad you appreciate the blog. I definitely prefer to do as much as possible within Aperture and avoid round tripping whenever possible. I'll try to do more blogs that concentrate on using various controls in Aperture to make image adjustments.
David Medina
2007-11-14 07:41:50
Much appreciated. One thing lacking in the Aperture realm is good digital darkroom book using Aperture. Sure, there is a few good basic book that tells you what each tool is suppose to do, but I would love to see an Aperture book that deal with real solution to real life situations. This kind of articles sure helps.

One thing I have found is that I seem to have more fine detail control in Aperture but Lightroom is easier to use. Looking forward to Aperture 2.0... hope is around the corner now that Leopard is out of the bag.

Ellen Anon
2007-11-14 07:54:14
David, we included a very large section on the digital darkroom adjustments in our book Aperture Exposed; The Mac Photographers Guide to Taming the Workflow (Anon and Anon, Sybex 2006.) Since it was written originally for version 1 of Aperture we made a free v1.5 pdf available on our websites (www.sunbearphoto.com) If we do a similar book for a future version of Aperture I can assure you it will have a large section on the digital darkroom because that's one of my main interests. And I share your hope that Aperture 2.0 is "around the corner!"
2007-11-14 11:18:50
I couldn't agree more, lots more info on the "develop" and less on "workflow" would suit me fine. I want and need the how-to's, the walk throughs, you name it.

I can't help but think that Aperture needs a strong evangelist like Scott Kelby with a 7 point system or something similar. Don't lock it all up in books or in paid websites either. Lots more free stuff on the web would go a long way.

That's my 2 cents. Keep up the great work!

David Medina
2007-11-14 11:22:27
Thanks for your response. Yes, I got your book... it was the one that got me seriously interested in Aperture. I think you did a great job in that book. Thanks for letting me know about the 1.5 pdf which I don't have. I will go and get it.

It would be really nice to see something like it was done for LR by Mikkel Aaland in the Lightroom Adventure done for Aperture.

I hope that for Aperture 2.0 we get a faster and smoother Aperture with some global presets and more selective tools like we see in Nikon Capture NX.

2007-11-15 21:32:13
Another call for more info in the digital darkroom. In lieu of that is there a way that you or someone could explain the top basepoints and the lower slider adjusters in the Level adjustment tool?

I have the Kigi book on Aperture and also have read the Apple pdf about making adjustments, but it still doesn't intuitively make sense to me.

Would it be fair to say that the tool is similar to the Curves tool in LR (I like the fact that in LR, adjustments to each point is shown as within an gray envelope in the Curves window)? So in that case, moving the upper basepoint in the Aperture Levels window is increasing brightness for the set of pixels base around the respective mid or quarter base point and moving the lower adjustment sliders is like shaping a contrast curve based around the respective mid or quarter point?


Ellen Anon
2007-11-16 04:49:25
Ed, think of the top points as controlling which pixels are going to be modified, and the bottom one as controlling whether they will be adjusted to be lighter or darker. The top point is similar to where you click on a curve in Photoshop and the bottom point is whether you drag the curve up or down.
2007-11-16 18:29:36

Thanks for your clarification. There just seems to be such different descriptions of and nomenclature for the basepoints and sliders in different reference literature! The Apple "Performing Adjustment" guide seems to suggest that the sliders are for contrast for the quarter tone sliders, but is a brightness adjustment for the midtone one. The later on, it mentions that the upper basepoint sliders can be set for different brightness depending on where the points are set along the levels histogram.

The Kigi document suggests you can replicate PS curves with the Levels tool (which I believe you can). It seems to say that the upper sliders move regional brightness, but it is the difference between upper and lower slider positions that give contrast to that region.

If and when you do write a book on Aperture about this subject, it would be great if you could give consistent and detailed workings of the upper and lower sliders and the interaction between the two as well as showing what the effect of each adjustment for each slider is on the histogram. It would be much appreciated!!

Anyway, on to more experimenting...


Scott Hampton
2007-11-30 11:49:33
I have one question. Why is the exposure set? Is it because it wasn't set correctly during capture, and therefore necessary to fix it in post?
Ellen Anon
2007-11-30 12:00:31
Scott, the ideal in camera capture is one that captures all the information as far to the right side of the histogram with no clipping in either the highlights or the shadows. However that's not always possible and further the best final optimized exposure may be quite different. Cameras see things differently than our eyes and sometimes in order to replicate what we see, we need to increase midtone contrast, for example. The image in the blog was correctly exposed but what it looked like to my eye was closer to the two middle examples, and at times, close to the last example, depending on the sun angle. You expose to the right, even if it makes the image look a little too light initially to capture the most information and least noise.
Scott Hampton
2007-12-02 09:37:31
Thank you. I appreciate the reply. It makes sense!

Do you have any articles about setting the black and white tints? I'm leaving Photoshop for the majority of my post work ad would like to use Aperture instead.

Again, thank you!

Ellen Anon
2007-12-02 09:43:10
You're welcome Scott. Check out my blog from 11/28/07 here. It was all about the Tint Wheels. I too use Aperture for most of my processing.


Scott Hampton
2007-12-02 09:50:44
I found some articles that you wrote. I'll look there.