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Tutorial - Rescuing over and underexposed images


Although it is very important to get exposure right at the time of image capture, there are times when even the best of us accidentally get the exposure wrong. Sod's law says that this will happen on your best shot.

If you shoot in RAW there is a much bigger exposure latitude than if you shoot jpeg. This offers a better chance of rescue, but what we are talking about here is really trying to make a silk purse out of a pigs ear.

Under exposed image

There is often a lot of hidden detail hidden in the shadows of an under-exposed image, but in opening up the shadows (e.g. with curves or levels) a lot of ugly digital noise will be revealed.

In the first example below, I was trying to photograph a hawkowl attacking a vole in very poor light - it was beginning to snow. I knew that if I did not achieve a shutter speed of around 1/3200th of a second the picture would contain motion blur. I was shooting at high ISO with an old 1DmkII camera and even with my f4 lens wide open I could not achieve this shutterspeed without under-exposing the image. So what can be done in post-process to correct it ?

I tried using the highlight slider in Levels but this badly exposed noise and burnt out all detail in the snow.So I used the following method:

In Photoshop, open the layers palette (Window>Layers)
Next duplicate the background layer by dragging it over the Create New Layer icon (second from the right on the bottom of the layers palette).




Next set the Blending Mode to Screen in the drop down menu. (See image below). You will instantly see the image brighten. Repeat by dragging the background copy over the New Layer icon until the image is just a bit brighter than you would like it to be.




Finally reduce the opacity by clicking on the arrow to the right of the Opacity box and adjust the amount to taste. When you are satisfied, click the small down arrow (above the Opacity box) and select Flatten Image from the drop down menu.

I put a few finishing touches to the image by adding some shadow detail to the snow with the Shadow/Highlight tool (which is covered in another tutorial), tweaked the midtone slider in Levels, sharpened it and saved as usual. This was the finished result below:





Overexposed image

To deal with an overexposed image an identical method is used to that in the underexposed example above, but this time the blending mode to use is Multiply.

This image is of a wildebeest crossing in Kenya and is overexposed.



Once again I duplicated the background layer but this time I chose Multiply from the drop down menu. I lowered the Opacity to 53% which looked good to me and flattened the image. After tweaking in Shadows/highlights and Levels I sharpened the image and saved it. Some of the brightest highlights are still a little burnt out but I think you will agree that this is a massive improvement to the original image.






 

 

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