What would life be like if we didn't make mistakes every now and then? In the case of photographic slide film it is not forgiving if you don't nail the exposure perfectly first time out. Take for example the image below, it's a fully fledged Photo Disaster! It's horribly underexposed and I was certainly kicking myself for bungling the exposure. But on closer inspection there is actually some image detail hiding away in this picture. Maybe all is not lost and with a little help from Photoshop I will attempt to bring this image back to life. I started by going ahead with a straight scan from SilverFast (scanning software for my Polaroid SprintCcan 4000) and bringing it into Adobe Photoshop. Some might advocate the use of working in 16bit mode in SilverFast and in Photoshop. Unfortunately the scan preview in 16bit from Silverfast was completely black! I believe it's better to start with something in 8bit and just move forward. This technique will most likely not work with Colour Negatives. Under-exposure and the removal of the orange base layer will result in too much noise and film grain to get anything useful.

Looking at the Histogram in the Levels dialogue below reveals the sad truth that all the image data is contained in the shadows. Using Levels alone to try to correct this image would be much too harsh. With Levels there isn't the control and subtlety that is available with Curves to gently coax this image back from the brink. Cancel Levels, and on to the Curves Dialogue.

What we need instead is a very gentle Curve. It's important to make sure that it is quite steep through the Three Quarter and Mid Tones, but also that it is very even in it's distribution. A rougher curve would easliy result in too much posterization in the shadows.

After the Curve is applied it is surprising to see just how much image detail there really is in this photo. This is a good start but another correction is necessary as there is a Magenta-Blue cast in the shadows.

Checking the Histogram after the first curve has been applied (below) shows a much better distribution of pixels throughout the image. The overall contrast is still a little low especially in the highlight area. Another curve will be required. It's important to note that how good the Histogram looks in Levels is dependant upon your Preferences for Image Cache in Photoshop. With Image Cache turned on the Histogram will appear smooth and even like the one below. With it turned off it will appear much rougher showing gaps or combing throughout. Of course the larger the corrections the more data that is lost in the image. You can only make so many corrections before an image will start to degrade in quality. Regardless of what the Histogram might look like what really matters here is that we can actually save this picture!

Another curve to increase and snap up the overall contrast. As well as some small moves in the Three Quarter tone areas of the Blue and Green Channels (not shown).

And now the final version below. A very useable photo with only two moves! I should point out that an image that has had such massive corrections applied to it should be examined very carefully. Look at each Channel individually to see if there are any major problems. In this case the shadow areas do show a fair amount of noise but mostly in the Blue Channel. So it is actually possible to rescue a very badly exposed image using Photoshop. It might not be the best quality image but if it is an important one you can bring it back to life. By the way, the bright yellow-green is a Lichen that was growing on the side of the barn and is naturally that colour! No Photoshop trickery there!

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