In our Part I Post on Scanning Negatives – Hardware Considerations we discussed the properties of light, film and glass (lenses) in making the perfect photograph. We then showed that these same properties are used to scan the negatives or slides when turning them into digital images.
Here we discuss the aspects of light, glass and CCD’s in negative and slide scanners. We also compare this to a Nikon Coolscan 5000 ED to see if it fits the bill to create the perfect digital image.
We have the perfect negative so what light do we send through it to make a digital image. CCD’s are especially senstive to Red, Green and Blue light, hence the RGB designation in computer lingo. In order to scan a color image, slide or negative, the scanner should produce a red image, green image and blue image of the negative or slide. These three images can be combined as if they were created from a digital camera.
Dust and Scratches
Realistically, even a perfect negative or slide will contain dust and/or scratches. Digital images from CCD’s in a digital camera are better protected although the newer cameras have modes to remove dust from the sensors. So how do we limit the scanning problems with scratches and dust on a negative or slide?
The answer is infared. Infared light can highlight scratches and dust. By creating a fourth layer used as a mask, signficant amounts of scratches and dust can be electronically removed from a scanned image.
The glass that the red, green, blue and infared light pass through to get to the CCD and result in a digital image, must be special photographic glass. In fact, the scanner should use the highest quality glass used in camera lenses. After all, focusing on a negative to create an image is nothing more than taking a phtograph of a photograph.
There are a variety of mineral glasses and low dispersion glasses available to create a proper scanning lens.
Film – CCD Sensor
The CCD sensor is the film for the scanner. The size of the CCD chip and the density of the pixels determine the quality of the resulting image. Larger size and higher density is similar to low speed film and should result in a higher quality image.
Because computer chips have occasional power spikes and other electronic interference, a simple one pass scan is insufficient for a perfect image. Using a single scan will produce errors in the scan with zero chance of help removing the imperfections. I.e., a second scan of the image will help the processor determine if any pixels are not properly rendered from the first scan.
Density of the scan is determined by dpi or dots per inch. The more dots that get scanned in a single inch of negative or slide, the more detail from the film will show through. In some cases, a scanner could even scan the grain of the film if it were dense enough in the CCD.
A film scanner should have the ability to scan negatives with a final optical output somewhere in the 3,500 dpi to 4,000 dpi and above.
Finally, what level of colors and/or gray need to be recoded? How many colors should be kept? The same problem occurs in photography prints. Photographic paper has a smaller range to record black and white images than the film contains.
Nikon Coolscan 5000 ED
How does the Nikon Coolscan 5000 ED scanner stack up against our requirements? First, the case is very sturdy, well put together and protective of the computer inards.
Let’s discuss the Light component: This Nikon scanner uses all three R,G and B lights by using LED’s and contains a fourth – the infared LED to help with scratch and dust removal. The LED lights use less power and also last longer and cost less.
The glass used in a Nikon Coolscan 5000 ED is the same extra-low dispersion glass found in Nikkor lenses. This limits the abberations that could be found in the resulting digital image.
The CCD is also strong in the Nikon Coolscan containing two lines to scan at a time and scans using optical resolutions of up to 4000 dpi. The scanner also contains a 16 bit converter so that the scanned images contain 16 bit color.
There are many other feature in the Nikon Coolscan that make it appealing, like the built in Digital ICE, USB 2.0, slide feeders, negative feeders, TIFF formats in greyscale and color and more. However, all those features aside, the physics behind the Nikon Coolscan make it a worthwhile investment to capture negatives and slides and turn them into digital images.
The Nikon Coolscan 5000 ED is my scanner of choice and we will provide some test results to see which settings are best to use when scanning media into digital images.