Epson FilmScan 200 Service Manual page 44

Figure 2-15 shows the sequence of operations, starting from the point where image data is input
into the FilmScan 200, and ending with the output of image data to a computer.
Original
Image Frame
CCD
Optical Unit
Shading
Correction
1. The lamps light, and the scanner reads the white standard attached to the inverter lamp cover via
slit of film carrier.
2. The lamps turns off, and the scanner reads the black standard.
3. The lamps light. Light passes image frame on the film is read by the CCD sensors.
4. The data that has been read in is amplified.
5. The amplified analog image data is converted to 10-bit digital data by the 10-bit A/D converter.
6. Shading correction is applied to the 10-bit digital data. The white and black standards [read in
steps 1 and 2, above] determine the shading correction.
Notes: Shading Correction
The image data sent out by the sensor is derived by direct photoelectric conversion of the reflected light
that impacts the sensors. This data must be further converted before it can be output from the device
(e.g., before it cam be used for reproducing the image on a CRT). The use of white and black standards in
performing this type of conversion is referred to as
determined from the following expression:
In other words, image data is calculated in-terms of its-proportional relation to white data. This scanner
converts data format from 10-bit to 8-bit at the "shading correction."
7. Gamma correction, color correction, zoom correction, and half-toning are performed, based on
commands sent from the computer (they re selected and adjusted by the TWAIN driver).
8. Image data is output to the computer device, such as monitor or printer.
Rev. A
A/D
AMP.
Converter
8 bits/ pixel Gamma
Correction
Figure 2-15. FilmScan 200 Operation Outline
(image data - black standard) / (white standard - black standard)
10-Bit / Pixel
Color
Zoom
Correction
"shading correction.'' The correction value is
OPERATING PRINCIPLES
Data
Halftoning
Output
2-11