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Photoshop Tutorial - Using the Shadow/highlight tool


The Shadow/highlight tool was introduced with Photoshop CS, and I consider it to be one of the most valuable tools to use if you want to get the best out of your images. It gives you the ability to bring out details in the shadows and highlights in a very controllable way.

Although it does not replace the need for fill-in flash, it does go some way in that direction, as it can lighten and bring out shadow detail - such as when shooting against the light without flash.

It can be used to help rescue a badly under-exposed image, can retrieve highlight detail in an over-exposed or over-flashed image, but more importantly, it can actually improve a properly exposed image by lightening up very dark areas of the image and toning-down very bright areas.

I could have given a spectacular demonstration of what it can do on improving a really bad image, but instead I have chosen to give you a more subtle, real-world example below with this barn owl:

Before
After shadow/highlight adjustment


Look at the barn owl's eyes - see how the dark areas have been lightened and give more life to them ? Now look at the detail around the beak and breast feathers - the highlights have been toned down to reveal more highlight detail. Although both images have been sharpened identically, the adjusted image looks sharper - as there is more apparent detail for the USM filter to work with. Finally, notice that the wing of the bird (with no important shadow or highlight detail) remains totally unchanged - a good thing.

How to use the Shadow/Highlight tool

I have read many technical descriptions on how to use this tool, but my eyes soon glazed over, and I still struggle to understand what the experts will tell you the various sliders are doing with the pixels. What I can offer instead, is a foolproof procedure for adjusting any image, with a demonstration of what each slider does in a practical worked example. So here goes....

Open up an image to work on. To practice using the sliders, I recommend using a picture of something pretty black (a jackdaw in my first example) and another containing a lot of white (a spotted flycatcher with white breast feathers on my second example).
I like to work on a 16bit TIFF image which has been converted from a RAW file, and has already had level adjustments made, but no sharpening, resizing etc.

To access the Shadow/highlight tool, click on Image>adjustments>shadow/highlight. When you open the tool for the first time, the image will change radically according to Photoshop's default settings - which will probably be totally inappropriate for your image. Ensure that the "Preview" box is checked - so you will see the changes you make actually happen in real-time. Also tick the "Show more options" button - as we need to gain access to the "Amount, Tonal Width and Radius" sliders for both highlight and shadows.

1.0 Working on the shadow areas

There are a lot of sliders, and they are all inter-dependant. Move one and it effects all the others seemingly. What we need is a way through this jungle - a foolproof method - and here it is... read on !

We are first going to see what the effect of moving the shadow sliders is, so we need to turn off the effect of the others. To do this:

Set both amount sliders to 0
Set both Tonal Width sliders to 0
Set both radius sliders to 50%. I will explain more later - but trust me on this for now.

Here is the image of the jackdaw viewed on the screen at 100% (click on the magnifying glass tool and select actual pixels from the top toolbar). All the sliders have been set as described above.

In the next screenshot, I have increased the Shadows "Amount" slider to around 45%. Notice how the shadows have lightened considerably - revealing more detail, but have not affected the light blue background behind the bird ?

If I slide the slider way over to 100% , the darkest feathers have lightened to a grey tone! The amount slider is pretty self-explanatory then. When we come to the highlight amount slider later on, it works in the same way but in reverse - as it darkens the highlights as the Amount is increased.



I got bored looking at our jackdaw's front, so lets move up to his head. I set all the sliders back to my starting values again. Incidentally, you can save these as your default settings by clicking the "Save as default" button - to prevent having to reset them each time.

Next, I have moved the amount slider to 75%. Notice that the darkest parts of the bird between
the base of the bill and the eye have lightened and the ruff of feathers at it's throat look far more detailed now ? Now, this is much as before, so now we will turn our attention to the dreaded "Tonal Width" slider.


In simple terms, if the slider is set to zero then only the very darkest pixels will be lightened. As the slider is moved to the right, slightly lighter pixels than the very darkest ones are also lightened - and so on, until midtone pixels are being selected and lightened too. To put it another way - a low Tonal Width value selects the darker pixels only, a high Tonal Width value will include progressively more lighter-toned pixels in the selection to be adjusted by the Amount slider.

In the example below, I have kept the same Amount settings as used in the previous image, but increased the Tonal Width to 24%. Notice how far more midtone grey areas have now been lightened too? I have overdone things intentionally a little to illustrate my point.


Finally we come to the mysterious Radius slider.You will remember that we preset this to a value of 50 pixels, which is in the right ballpark for most camera images of around 6-10 megapixels - as it is image size dependant. The slider should be tweaked for each image, and you will find that if you set it too low (try it at zero) you will notice a blurring of detail. The slider needs to be set according to how large the dark (or light) areas are. As you move it around, you will notice a definite "sweet spot" where image detail is maximised, and the midtone contrast remains unaffected

In the screenshot below, I have reduced the "Amount" to a more sensible 26%. adjusted the "Tonal Width" to 5% to select the darker tones only, and tweaked the Radius to the sweet spot - which came out at about 33 pixels. A subtle, but definite improvement on the starting image I think.



Finally below, I have demonstrated what happens if you set the Radius slider too low.
Compare it to the (good) screenshot above, and you will notice how the feathers on the throat
and the back of the head are far less sharply defined and the image has gone "flat" due to lack of
contrast.

 

 

2.0 Working on the highlight areas

Once you are satisfied with your shadow settings, you can move on to the highlights. If you only want to address the highlights, set the shadows amount slider to zero. Here is the picture of a spotted flycatcher. It should be said that the tool can not retrieve details in pixels that have completely burnt out to white, but it can often retrieve more detail than you would have probably believed possible.


The procedure is just the same as for the shadows, so starting at the same settings as for the shadows, set the Highlight sliders to: Amount 0%, Tonal Width 0%, Radius 50px settings.

Now move the amount slider to the right. As the Tonal width is set to zero, only the brightest pixels will be selected this time. Watch the white breast feathers darken and gain in highlight detail. In the image below, I went on to adjust the Tonal Width to just 3% ( to select just the very lightest pixels that I wanted to darken) and finally tweaked the Radius to the "hotspot" of 50 pixels.



I realise that it is difficult to see these differences on these very low low-resolution screenshot examples, so here are a couple of 100% crops which better demonstrate the kind of improvements that I am seeing on my computer monitor.

Before adjustment
After highlight adjustment



Finally, you may have noticed a couple more sliders called "Color Correction" and "Midtone Contrast." These may be used if you feel that the colour or midtone has shifted a little as a result of making your adjustments. I rarely use the Color slider, but sometimes images benefit from a bit more contrast, as by lightening shadows and darkening highlights simultaneously, you are effectively lowering the overall contrast. Conversely I have also been known to intentionally lower contrast in some images in this way that were taken in harsh light.

I strongly recommend you try using the shadow/highlight tool - I think you will be amazed at how effective it can be.




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