Often it is heard that the quality that can be achieved from scanners using a CCD method it can be compared to the method of the drum scanner of photomultiplier technology.
Mostly this is true but is necessary to make the difference if you are in the need for the best quality method. It can be said that the CCD method of scanning is not capable of providing the same level of reproduction that the drum scanners can offer at the moment.
Down below you will find reasons why the drum scanners can offer a better reproduction and more details about the drum and the flatbed in general.
This is the effect that all of the CCD scanners can produce. The flare effect can manifest as a halo in areas that are contrasting and close one to another, just like the white bars that are placed against the dark background. The consequence of this effect is that the definition of the edge that is sharp is lost.
Range of density
When it comes to the drum scanners, it is clearly that the photomultipliers are able to capture a wider range of density than the CCD scanners in flatbed devices can capture. The drum scanner can “see” a bigger depth of colour. More than this, the flatbeds can use different softwares to expand the ability of scanning in a bigger density range and to do this in an artificially way.
What is characteristic for the CCD scanner is also the way that is can go blind when the end of the density limit occurs and as a result, there is a noise that is created when the image is scanned. This does not happen with a photomultiplier because of the capacity that it has to resolve the densities that are high regarding their values.
The CCD range of density restrictions might give the risk of the scanner not seeing all of the shadows in details and in different transparencies and this is why the scanner can not reproduce some areas fully.
Most of the times, in the majority of happenings, the scanners with CCD can be limited to 5500 dpi that are used for a better and true optical resolution. The drum scanners benefit and provide their customers 12000 dpi in the optical resolution, which is better quality than the CCD.
The need for a resolving power like this is questioned, but the ones that require this quality understand the need for this capability. The files that are large in size ( about 1-1.5 BG) are usual and they are used for long terms.
In most workplaces, there is a problem with the dust because it can not be avoided and for a scanner device, the dust is one of the biggest enemies. The thread seems to be worse for a flatbed than with a drum.
If any particle of dust gets on a sensor from a CCD scanner, it can cause different streaks across the image that is in the process of scanning and in can disturb its direction. All sensors have one blind spot. When it comes to the drum scanner, if a particle of dust gets on the scanner sensor, the photomultiplier can make the problem small in size and overall the affected area will turn to be less significant.
With only one opening of the lid of a flatbed reader, you can cause problems if the air gets to be sucked into the bed zone of the scanner and the dust can get drawn in places that you don’t want it to get. If this is a problem for the flatbed scanners, for the drum scanner, it is not.
The drum scanner
A regular drum scanner contains a drum that is shaped like a perspex cylinder. Inside of the cylinder, there is a periscope that looks that a normal tube and a lens that is supposed to face the head of the drum which analyses the situation.
The method implies a point of light that is supposed to be emitted (internally or even externally) to the drum, but with the correspondent type that it originally has ( with reflection or with transparency).
It works with the source of light that moves at the same time as the assembly moves, down the length that the drum has and as it does actually spin around at a speed that can make the device capture the information, line by line and space by space. The light then goes through the lens into the prism and there the light will separate into two and direct to the multipliers.
This is how the light gets converted into electric values and after this step is completed, the values are processed and transformed into digital data.
The flatbed scanner
This type of scanner can work in strips, not like the drum reader works, with points that are considered to be fine. Provided with wide strips, the source of light and the head that reads the information are placed with the illuminating lamp into the bed.
The head that scans is the part that has inside three CCD arrays. With this method, the light can be reflected or sent on to a mirror or more and then it can be passed using a lens, across the CCD.
CCD is a transistor that emits electrical signals that are tiny and at the time when the light hits the signals, they are transformed into digital data, just like the light sensitive devices work. The mirror inside and the source of light both move down the flatbed and let the CCD scanner head to capture the image line my line and space by space.
As a final judgement, it can be said that the scanners that are based on CCD are able to produce results that are acceptable. It is true that they do not reproduce the colour very good, but that depends strictly on the requirements. It is actually easy to notice that the drum scanner can be a better tool that you can use for a better quality of the images that you want to scan.