Shadow/Highlight Adjust tutorial

Understanding Digital

Photoshop Techniques - Shadow/Highlight Adjustment

Here we have an underexposed image of a robin which, exposure error aside, is actually quite nice - it's sharp and the composition isn't all that bad so it would be nice if we could make it into something at least halfway decent.

So let's get on and open the image in Photoshop CS3 (2 will be fine) and see what we've got.

Now straight away if we look at the histogram we can see the underexposure - everything is crammed into the left side of the graph. We can also see that there are some big variations in pixel density, the very dark tones are in the lowest portion of the histogram on the extreme left, then suddenly, there's a big jump and a lot of "spiky" peaks containing our mid-tones and highlights, but they are very compressed laterally, side-to-side if you like, and that tells us something else about the image, it's low in contrast, which I'm sure you can see for yourself in the actual image.

Now some folk might start to make adjustments to this image using either the LEVELS adjustment, or the CURVES adjustment.

In my opinion LEVELS is a bit crude and rudimentary, and CURVES, well, it's the spawn of Satan, rather like Camera RAW, DNGs and diesel!

The Shadow/Highlight Adust feature in CS is a lot more refined and in most cases is the only major image adjustment you'll ever need to rescue yourself from the average exposure 'faux-pas'.

So let's go Image>Adjustments>Shadow/Highlight:

If, when we've done that, we see the dialogue box open in its compressed form as below then simply left click the check box (circled).....

....and we should end up looking something like this.

Now on your machine the image has more than likely changed beyond belief and won't be looking like this - that's because your default settings are as Adobe shipped them with values already entered, and because I'm a bit of a smart a*se and have reset my defaults to "zero everything" so it always opens with no effect.

It doesn't really matter either way as once we start moving the sliders around the end result will be the same.

So go ahead and start moving the sliders around - 'have a play' - as long as you don't click 'OK' you are perfectly safe!

I think these settings look pretty good - it certainly looks a heck of a sight better than it did!

The real point of interest is the histogram - look what's happened.

The black histogram is the 'now' version, and the grey one is the 'before' - you can see we have in effect added a considerable amount of effective + exposure compensation (we've moved the histogram to the right and increased the luminance values) and the whole graph is a bit wider; we have increased the tonal range and so increased the mid-tone contrast.

But we haven't touched the mid-tone contrast slider.

I'll bet you are wondering what that little hazard warning triangle is in the histogram box - well wonder a bit longer - we'll come back to that in a moment or two.

At the bottom of the adjustment dialogue box you can see two more potentials for adjustment, Black Clip and White Clip.

Now these two characters are quite easy to understand if we have another play whilst paying attention to the histogram.

You can change the values of both anywhere from their default 0.01 value right up to 50.0 - so let's go mental and dial 50 into the black clip value.

Crikey! That's a bit shocking - but we can gain some useful information if we look at the histogram.

In the previous image you'll notice that the blacks had moved further right along with everything else - in other words, they were not black anymore.

Now, the blacks have moved to the extreme left of the histogram - okay, so has everything else, but it's just worth bearing this in mind.

Let's now put the black clip value back to 0.01 and enter a value of 50.0 for the white clip.

"Robin at the Point of Thermo-nuclear Detonation" - not marketable really but it was worth a punt!

Now everything has shifted to the right, but if you examine the blacks in the histogram you can see that they are very strung out and haven't really moved quite as much as everything else.

So if we consider what we've just learned we can deduce that a small amount of black clip adjustment might just make the blacks a bit blacker and a small adjustment to the white clip value may well expand the highlight a little further right on the histogram.

Now we can see we've moved the blacks a little further left by changing the black clip value, the highlights and lighter tones are quite a bit further right, and we have ever so slightly more tonal range.

And we have STILL not made any direct contrast adjustments!

Now, that little warning triangle. It means that Photoshop has uncached data for the histogram - if you click the triangle...........

.........the histogram gets re-drawn.

This gives us a better indication of what our image looks like, but the histogram panel would make a tutorial in itself and for the moment all we are concerned with is our little robin, and I think he looks a lot better.

So, we started out with a low contrast and under exposed image.................

.......and ended up with something that I'm sure you'll agree, looks half decent and there wasn't a curve or level adjustment in sight!

Don't get me wrong, adjustments to the levels and curves have been made, but behind the scenes.

Virtually every kind of image adjustment technique in Photoshop makes level and curve adjustments, after all, there's nothing else to adjust really, but they all work in different ways in order to achieve the same thing - it's just that some are more controllable and easier to handle than others.

It just goes to show that there's more than one way to 'skin the cat'!

Hope it's been useful folks!