Underexposed JPEG Before & After

How to rescue underexposed JPEGs

Techniques

01 August 2008 15:53

Underexposed JPEGs are much more difficult to fix than underexposed RAW files. How many times have you taken some shots on a compact camera and suffered at the hand of underexposure? We all suffer from this problem occasionally, as random as a bolt of lighting of course, but it does happen.

RAW conversion software offers control over exposure and brightness making the rescue of underexposed images quick and easy. JPEGS on the other hand are only editable in programmes such as Photoshop, which doesn't offer these controls. However there is a way round this problem. Follow this simple step-by-step technique to fix your images in a matter of minutes.



Step 1

Here is the start image taken indoors and extremely underexposed; the only parts that are correctly exposed are the windows. The first thing you need to do is make a copy of the background layer (CTRL+J) when working on this layer (or Layer > New > Layer Via Copy). The next thing to do is set the blend mode of this new layer to Screen. If your image is still too dark, make a copy of this new layer and continue to copy each new layer until you’re happy with the results. If you find the results are too light, you could change the opacity of the top layer to achieve the desired results. With the image used here, five background copies were made and set to Screen at 100% opacity.

Step 2

The next problem you will find will be a serious lack, or addition of contrast. Different images behave differently so I will show you how to fix both. The image used here suffered from too much contrast so I created a backwards S shaped curve. If your image requires more contrast, a normal S shaped curve will add more.

Below is the final image. The quality isn’t close to a well exposed shot, but the image has been saved.


Step 3

All that is now left to do is flatten the image to reduce the number of layers and the file size. Each copy of the background layer will increase the file size so a 5mb image with four background copies could be five times that size. To do this go to the black arrow at the top right hand corner of the layer palette, and click Flatten Image.

While this technique can to some extent save ruined images, you’ll never get perfect results. But on those occasions where important shots have apparently been lost, there could be a remedy. However, one of the main problems with using this technique is the amount of noise, lack of contrast, or too much contrast it can produce. You’ll also never retrieve information from the darkest shadows but this a small price to pay.

One thing to remember is the less an image is underexposed, the more successful technique will be. Underexposure is generally easier to fix than overexposure. Photoshop is more successful extracting information from dark shadows and mid-tones than it is with blown highlights and lightened mid-tones. If your images are overexposed, follow this guide using the multiply layer blend mode to darken your image instead of Screen to lighten. You will see that the image can’t be pushed as far this way.