Rescue old color-degraded photographs

Those are the most commonly used image editing applications (Aperture only on Mac OS X) which allow you to colour correct photographs. SilverFast has become the industry standard for scanning software, and as most scanners come with at least SilverFast Ai SE included, I have decided to cover SilverFast Ai. However, in this tutorial I'm discussing SilverFast Ai Studio, which is the "professional" version of the application. Some dialogues will look different, but by covering the Studio version, you will learn how to work with all versions of SilverFast Ai.

Some high-end scanners like those distributed by Heidelberg, include the Ai Studio version of this powerful scanning program, so you're in good company if your scanner includes SilverFast -as it almost certainly will. If you are going to scan a lot of photographs, take my advice and buy the Studio version of SilverFast. It comes with a lot more than just colour correction.

For the examples in this tutorial, I used a Power Mac G5 1.8 GHz dual processor machine with 2.5 GB of internal memory and an ATI Radeon 9800 SE with 256 MB of VRAM. The monitor was a LaCie photon20vision calibrated using X-Rite's MonacoOptix XR2 colorimeter.

All examples in this tutorial were created with this system and throughout the tutorial I will only refer to Mac OS X based applications. I think the machine is quite typical of what you will find at the average desktop publishing service, ad agency, or photographer.

This is not to say you can't benefit from this tutorial if you're on Windows. Only Aperture and iPhoto are Mac-only products. SilverFast and Photoshop both come in Windows and Mac OS X versions. However, some details like the soft-calibration that is available on Mac may not be available if you're working with Windows XP. As I don't know enough of the platform, it's up to you to find out if there is such a tool or not.

Calibrating your monitor is essential. If you don't have a spectrophotometer or colorimeter, you can use the Color tab of Apple's Displays Preference panel. There you will find a "Calibrate..." button which allows you to calibrate on view.

When you use this method, bear in mind that the human eye can be quite easily fooled with regards to colours and certainly with regards to slight colour shifts and hues. If you're colour blind, even in the slightest way, you shyould refrain from "soft-calibration" altogether, and rush out to buy a calibration utility.

If there's nothing wrong with your eyes, but your budget doesn't allow you to buy a calibration utility, or you don't feel like spending money on one, even calibrating by actually looking at colour shades is better than nothing at all. Do use the Advanced procedure, however. Set your monitor to a gamma of 2.2 and a colour temperature of 6500 degrees Kelvin. And try to work with the system under roughly the same lighting conditions as when you calibrated the screen.

Colour casts

Not all colour casts are disturbing. Some are actually very pleasing. Most photographers will look for the colour cast of a strong sunset or a bluish ocean. A photograph taken at sunset will have a strong yellow/reddish colour cast but we will find that rather pleasing because it recalls an atmosphere. The photograph communicates in good part because of the colour cast.

Old, degraded photography, however, have colour casts due to the ageing process. They turn yellow, muddy brown, or purple. Often they get less detailed as well, with colours and details fading. Equally often these colour casts will not be uniform throughout the image, and they will not convey an atmosphere or an emotion. They will be blotchy, further adding to an unpleasant look and feel. In short, such discoloration will make you think of fungus rather than of a warm, cosy atmosphere like with the sunset photograph.

You can repair such photographs yourself in most cases. In fact, if the cast isn't too severe and detail is still there, you will be able to return old photographs close to the original state you remember them being in with only a few clicks of the mouse. For badly discoloured images, it will take some more tuning, but you will be able to get them right in 99% of the case.

Before we jump in and start correcting colour photographs with SilverFast, you should know about the two methods to judge and correct colours and images in general. There's the viewing method and the measurement method. The viewing method totally relies on what you see on your screen. It's the least dependable, because lighting conditions will change the way you perceive colours from day to day. However, with a calibrated monitor and a bit of luck, you will be able to judge and correct most images and colour casts without problems.

You should make sure you're always printing your corrected photographs with the Rendering Intent setting of the printer dialogue set to "perceptual". With most inkjet photo printers this will be the setting you will preferably be using. In Photoshop CS2, the Rendering Intent pop-up menu becomes visible only after you've made the Color Management panel visible by clicking the Color Management disclosure triangle.

The Perceptual setting will make sure the colours in your photograph are represented as perceived. This is the appropriate setting for photographs which must be printed with as large a gamut of colours as possible. The other rendering intents will compress the image's colour gamut into a smaller gamut. The result --for some rendering intents-- is that some colours may be thrown away and will not print at all.

The second method, the measuring method is far more accurate, and often the only viable method to get good results. The measurement method uses a software-based densitometer or a spectrophotometer --this is the measuring tool, often an eyedropper or pipette-- and a histogram to represent the spread of the tonal values and colours in an image.

Just for the sake of completeness: it is even better to use a hardware spectrophotometer like the GretagMacbeth Eye-One Pro or the X-Rite Pulse

The densitometer is the software equivalent of your calibration utility. It is a software spectrophotometer tool that measures the colour values under the cursor. The densitometer in SilverFast and Photoshop both are very accurate and efficient measuring tools.

Neutral areas like white, all shades of grey and black must read out equal or near-equal values. Coloured areas will read values that are appropriate for the colour being measured. Bright red, for example, could give a read-out of R=255 * G=5 * B=2. The problem with the pipette values is that you must get used to converting the numbers that you see to colours in your mind.

It may be hard to just come up with the colour when looking at the figures, and it does not become easier when measuring colours and reading the values, and then visualising what the colours should be (unless with a lot of exercise, as with most things in life).

The histogram is your second instrument for measuring and viewing colour and tonal values. This is how the histogram looks in Photoshop CS2 when it's completely expanded: For now, we will leave the histogram alone. It's good to know you have a powerful tool to see how colours are spread across an image. Still, I should already warn you that a histogram that looks very narrow or very skewed in one direction is not a bad sign per se.

It all depends on the circumstances in which the photograph was taken. For example, dark scenes usually have a skewed histogram -one in which the tonal values hover around the dark side of the spectrum. Photoshop CS2 is not the only application with a histogram. SilverFast has an extremely powerful one, Aperture has one, and even iPhoto has a histogram.