I doubt there is a single tool in all of digital post processing that is more powerful than curves; yet with that power comes a rather daunting interface that causes many to shy away. That’s unfortunate, because a photographer with a firm grasp of curves can make some wonderful things happen. Let’s see if we can’t make this tool a bit less intimidating.
I am going to start with an image my wife took on a recent trip to Cambodia. What can we tell about this image? First, it looks a bit overexposed and the blacks aren’t truly black. Much of the flowers appear to be blown out and the overall coloring looks faded. Let’s apply some classic curves and see what happens.
The first is a darkening curve. Simply grab the middle of the curve and pull down; the entire image will darken. We could have done the opposite and lightened the image by pushing the curve up but in this case the darkening appears to be an improvement.
Next we are going to apply a classic contrast curve. Click on the very middle of the graph where the vertical, horizontal and angled lines intersect, but don’t move it. By doing this we freeze this point where it is as we make other adjustments though we can still return and adjust this whenever we wish. Now, choose a point halfway between the middle point and the top right hand corner and push up. Then choose a point halfway between the middle and the bottom left hand corner and pull down a bit. The net effect should be that the lights get lighter and the darks get darker, therefore increasing contrast. We could have done reduced contrast by doing the opposite and perhaps that would have been a better choice as this image clearly does not need more contrast.
These adjustments alone would make curves a powerful tool, but we can go much further. We go to the Channels selector, which is reading RGB right now, and select just one of the channels to make adjustments. Below I have gone through and made adjustments to each of the channels. Look at how each is represented on the graph and how each channel has a separate and distinct curve.
OK, I overdid it, but I was trying to make a point here. Curves offers the power to make very significant adjustments to your images. Is it easy to go too far? Absolutely, but don’t let that scare you away from one of digital imagings ‘Power Tools.”
Finally, go back and compare the before and after. Parts are still slightly overexposed, but we have made significant improvements in overall color depth and tonality. Would we benefit from reducing the curves just a bit? Yes, but now that we have an understanding of the tools, that should be an easy fix. Oh, and don’t let me forget to mention that curves is a “destructive” process: pixels are being moved and changed, so always be sure you do this on an adjustment layer so you can return to your original if need be.
Trust me when I tell you this is only scratching the surface of what is possible in curves. There is lots more that could be done but will have to be left for another tutorial. My only hope is that you will have the courage to dive in at the deep end and try the possibilities for yourself.