KEN McDONALD

There are certain times when the lighting situation can fool a camera’s meter into giving a false reading... The camera calculates that all scenes are an average 18% grey, which of course we all know they are not... Predominantly white objects, or scenes that have a lot of reflected light like snow scenes, water scenes, beach scenes, or landscapes with a lot of sky in them cause under exposure... The camera's meter averages everything out to a mid grey, so if the image is predominantly light it makes those light shades mid grey by under exposing... Very dark scenes tend to cause over expose in the image because the camera tries to lighten those dark areas to 18% grey by over exposing the scene..

On the left you will see an image which is predominantly white, a white sign on a white door... I will try to explain the methods I know to help correct this exposure error and show the results for you to compare...

I deliberately made no ‘in camera’ compensation for this brighter than average scene, and as you can see by the result is less than acceptable...

The cameras meter has been fooled by the brightness of the scene and rendered the image about 2 stops under exposed...

You will also see from the histogram on the left that there are no true whites in this image...

There are however ways of trying to correct this in Photoshop, some better than others...

AUTO CONTRAST

This is one of the easiest methods to try and save this under exposed image...
This method only takes a few mouse clicks and requires no post processing skills at all...

1... Click on Image from the Menu bar...

2... Select Adjustments...

3... Click on Auto Contrast...

This does a pretty good job but the only problem with this method is, because it´s an auto adjustment you have no control over the final outcome... This method in my opinion still leaves this image slightly under exposed and more adjustment would be necessary to achieve a good result... This method however is always worth a go because in less extreme cases it can do a fine job...

This method can give very reasonable results with care...

1... Click on layers tab or press F7...

2... Click on the New Adjustment layer icon shown below...

3... Select Curves...

4... Click and hold the left mouse button down on the diagonal line and drag it up and left until you achieve the desired correction...

Of course if this was an over exposed image you would Click and hold the left mouse button down on the diagonal line and drag it down and to the right... You can also select different points and create a sine curve to alter the effect...

LEVELS

This is my preferred method as it gives me complete control over the amount of adjustments to both blacks and whites...

1... Click on layers tab or press F7...

2... Click on the New Adjustment layer icon shown below...

3... Select Levels...

4... Move the white slider on the right, as shown below, towards the left until you achieve the desired correction...