Spectrophotometer

Jan 28, 2002

Deryck HongSuryadi Gunawan

Presentation Outline

Project Objective Project Specification Design Test Plane Power Consumption System cost

Project Objective

Building a measurement tool that is used to measure color composition– Measures light reflected from an object at each

wavelength.– Creating a color spectrum and measuring intensity

of each color.– Using the intensities to create the color of the

object and displaying the color on a screen with corresponding RGB values.

– The object has to be a piece of single colored paper

Project Specification

CCD sensor:– 2048 pixels

• Blue: 150 – 650• Green: 800 – 1300• Red: 1450 - 1950

– Intensity from 0 - 255 Lens

– Focal length of 80 mm Distance between object and lens is 5 cm Distance between lens and the CCD sensor is 13 cm Accuracy:

– Error within (10%)

Project Specification

Using C programming with GRX graphic library to create GUI

Communication between PC and the CCD sensor through parallel port

Color Spectrum

This project uses the wavelengths from 435 nm to 740 nm.

Design

Workstation

RGB values display

Output Color displayscreen

GetColor

Source Lens Diffraction Grating

CCDSensor

ParallelPort

Design Cont

The distances between parts have to be calculated:– Between Diffraction Grating

and the lens– Between Diffraction Grating

and the CCD sensor Distance between the lens

and the Diffraction Grating can be calculated using lens equation:1/Object distance + 1/Image distance = 1/focal length

Design Cont.

After finding the angles, the distance (D) can be calculated using the following equations:

and are the displacements from the central maxima to the maxima of blue and red lights. The difference of those two displacements has to be the height of the CCD sensor.

The height of the CCD sensor = 2048 * 14um = 2.867cm Then D is found to be 2.867cm/0.6172 = 5 cm

D

yD

y

22

11

)tan(

)tan(

1y 2y

RGB Intensity

0

20

40

60

80

100

120

0 500 1000 1500 2000 2500

Pixel Location

Inte

nsi

ty Red

Green

Blue

Division of Work

Hardware ( Deryck & Suryadi)– Mounting of parts – Casing – Placing of light

Software– Parallel port communication ( Deryck &Suryadi)– GUI ( Deryck )– Algorithm ( Suryadi)

Work Completed

CCD, Lens and grating have been mounted. Light has been placed. Casing is created. Light absorption is designed. GUI is done Parallel port communication between CCD sensor

and PC is done– Still have some small problems

System calibration is done– Pixels that correspond to Red, Green, and Blue are found

Work to be done

Algorithm is implemented but still needs to be fully tested.

Overall system testing Color Compensation for monitor viewing

Test Plan Use Color samples that has known RGB

values to test the system A set of color samples have been measured

using the device in the color laboratory in printing department– The device measures the LAB values of the color

samples– Then the LAB values are converted to RGB values

This set of color samples will be used to test the system.

Power consumption

CCD board……………………… 5 watts Light source…………………….50 watts

Total power consumed…….55 watts

System cost

CCD and lens……………………$1040 Grating……………………………$1 Casing…………………………….$ free Light source………………………$30 Misc (tape, black paper, etc)……$15

total $1086