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Gamma adjustment
Changing the midpoint to alter the balance between light and dark. This time we use an adjustment layer.
The techniques
The sample images for these tutorials are available for download as a zipped folder.
Please note. The images in this tutorial section are for personal non commercial teaching use only. If you are a school or other public educational establishment, you may use them as long as you inform Northlight Images of the use. They may not be used in -any- other way without the express consent of Northlight Images - see our usage and copyright page for more information.
Feedback is always welcome! ---
Northlight Images also provides commercial photography training courses for businesses, including specialist Photography training for Estate Agents and for Product Photography.
Setting the Gamma of an image is one way of adjusting the relative proportions of bright and dark areas – much the same way as in the midtones example. In fact it is just the same but we are going to use a layer. Layers are one of the most powerful features in Photoshop, but a lot of people are initially a bit wary of them. Here we are going to get virtually the same effect as in the midpoint technique. In fact you can go back to the midpoint image and try the adjustment with layers if you like.
Open the image Gamma.jpg
Rotate it 90 degrees (Rotate is in the Image menu)
(We are going to do the adjustment using a levels layer)
Create a new levels adjustment layer.
Accept the default name for the new layer created (a meaningful name can be useful if you are going to use lots of layers)
Raise the midpoint slider to darken the image to taste
Note that raising the midpoint moves more of the picture to below (to the left of) the midpoint – making it darker overall.
When you click OK the change is made.
So, what's different to doing the same thing with a midpoint adjustment like we did at first?
Click the little eye symbol in the layers palette next to the levels layer (highlighted above). The adjustment is gone. Click the eye again and it is back. This allows you to selectively turn off adjustments to see their effect (you could have lots of different layers)
Secondly, you can click on the layer (the histogram like symbol) and change the adjustment later. If you had just done a simple midpoint alteration, you would be stuck with the change and would have to start over from scratch. The layer does not touch the original image information below it. Layers make it much easier to experiment without messing things up.
Lastly, there many more effects you can do with the layer now you have it. We will cover some of these later
Gamma is actually quite a complex subject, with much more to it than making pictures look lighter or darker. Here is one very useful set of info on Gamma we found (probably -much- more than you really wanted to know)
The techniques
The sample images for these tutorials are available for download as a zipped folder.
Please note. The images in this tutorial section are for personal non commercial teaching use only. If you are a school or other public educational establishment, you may use them as long as you inform Northlight Images of the use. They may not be used in -any- other way without the express consent of Northlight Images - see our usage and copyright page for more information.
Feedback is always welcome! ---
Northlight Images also provides commercial photography training courses for businesses, including specialist Photography training for Estate Agents and for Product Photography.
Other areas of our site that may be of interest...
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Digital Black and White. Keith was recently interviewed about digital black and white photography for a magazine article. We have an expanded version here covering some of his thoughts, techniques and tips for those thinking of trying black and white.
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