Not actually a ‘scanner’

Although marketed as a book scanner all of the Unionovo systems are technically not scanners but digital capture systems.

This is because there is no scanning to capture the digital image as the system uses the latest Canon CMOS DSLR’s. This applies for any book ‘scanner’ using cameras or CMOS technology.

With the recent rapid development with DSLR’s and CMOS sensors it is quickly becoming apparent in the library and archive industry that the traditional benefits of using linear array are fading, especially when capturing smaller originals. Recent developments in CMOS technology give an increased pixel count and lower noise levels thus improving accuracy and simplifying set-up and capture time.

There are some major benefits of using DSLR’s for digitisation, such as:-

  • Much faster capture time
  • Depth of focus
  • Reduces the need for image manipulation
  • More flexibility

Complications

It can be said that traditional book scanners are easier to use than DSLR’s with camera stands and that only professional photographers can acheive the optimal results. In short the answer is yes, however with the right system, such as the Unionovo, the unnecessary complications are eliminated, taking the advantages of DSLR’s and making it as simple as a book scanner. The Unionovo systems take care of these complications – colour correction, lighting, cradling, reflections and camera settings, resulting in a very powerful digital capture system which is easy to use.

CCD Line Array vs Digital Sensors

tech-infoTraditional CCD Line Sensors have the capability of holding an extremely high pixel count as well as equal amounts of red, green and blue Pixels, however these so called ‘advantages’ are not necessary when digitising A2 or smaller.

The main differences regarding the colour is how the sensors are built. Most CCD line scanners use a Trilinear line sensor capturing red, green and blue along three lines of pixels. This means each colour is captured as ‘true’ as possible but actually past what is humanly possible to see! This sensor type also requires a large amount of light to be used during capture, which can lead to the breaking of ink on the original archival material. In addition the material has to be pressed flat by a transparent material and/or image manipulation is required to ensure a correct looking image. All-in-all this leads to a greater cost assoicatated with CCD Line Array sensors as compared to CMOS sensors.

CMOS sensors have recently experienced rapid development with the latest range from Canon featuring amplifiers at each pixel site which improves image processing and reduces power consumption. The colour filter for the sensor is a standardised Bayer Filter. This pattern alternates a row of red and green filters with a row of blue and green filters. The pixels are not evenly divided — there are as many green pixels as there are blue and red combined. This is because the human eye is not equally sensitive to all three colours. It’s necessary to include more information from the green pixels in order to create an image that the eye will perceive as a “true color.”

When it comes to digitisation of smaller objects CMOS technology is quickly becoming the favoured choice. This is apparent as more and more major and national libraries/archives are opting to use DSLR’s.

Difference in sensors

crop_factorTechnically there are a lot of differences between high-end and mid-range CMOS sensors which are both used by Canon in their DSLR range. One of the major differences is the actual size of the sensor. This can have an effect on the pixel count and in turn the optical resolution of an image but also the size of the pixel for image accuracy.

Canon’s high-end systems use a full frame sensor measuring 36 x 24mm with 22 megapixels.

The mid-range cameras use what is known as a crop sensor with a reduction value of 1.6x and with the pixel count varying.

Full-frame sensors have the capability of producing more accurate images, however then the lens becomes more critical, whilst a crop sensor will use the ‘sweet spot’ of the lens. Also there is an element of cost as full frame DSLR’s are often around 5x more expensive than crop sensor DSLR’s.

True Resolution

UniCapture, which is supplied with all of the Unionovo capture systems, allows for digital images to be saved at 600dpi, however this is by interpolation.

Here are the true optical resolutions for the Canon 700D and 5D mkIII over the A4 and A3 capture areas:

Canon EOS 700D

CMOS Sensor

Crop Sensor: 22.3 x 14.9mm

Total Pixels: 18.5 megapixels

Image Size: 5184×3456 pixels

A4 Optical Resolution: 415ppi

A3 Optical Resolution: 295ppi

Software capture: 600ppi

Resolution is rounded down to the nearest 5 pixels

Canon EOS 5D mkIII

CMOS Sensor

Full Frame Sensor: 36 x 24mm

Total Pixels: 22 megapixels

Image Size: 5760×3840 pixels

A4 Optical Resolution: 460ppi

A3 Optical Resolution: 325ppi

Software capture: 600ppi

Resolution is rounded down to the nearest 5 pixels