1. Announcements
After lecture, we will start with basic image processing using MaxIm DL
Dark Sky Night scheduled for tomorrow night (Wednesday). Weather forecast looks bad. Rain may end but still cloudy and very humid. Cancellation notice will be posted tomorrow by 5:00pm. If I do cancel, class will meet Thursday night. If clear (most forecasts say it will be) meet at the farm to do imaging. If not, meet here.

2. Digital Imaging

3. Basics: The Photoelectric Effect

4. Photoelectric Effect: The Theory

5. The MOS works on the photoelectric effect
By “catching” the liberated electrons in the MOS device you lose the frequency information. Thus, the MOS simply measure the intensity (# of photons), not the color.

6. The difference is in the on-pixel amplifier
CCD Versus CMOS
The difference is in the on-pixel amplifier

7. Each pixel is an MOS photodiode
The liberated electrons are held in the potential well until they are read out

8. CMOS includes amplifiers on each pixel while CCD’s do not
As a result, not all the area on a CMOS pixel is available to collect light. The amplifiers also tend to be nonlinear so they aren’t as useful for photometry

9. A CCD array has millions of individual devices
The smaller the pixel, the higher the resolution. But, the smaller the pixel, the fewer the number of electrons that can be stored before it fills up

10. Downloading the array is like running a series of conveyor belts

11. Downloading the array

12. If a pixel gets overfilled (saturated), it “blooms” into pixels down the line

13. Anti-blooming Architecture helps eliminate booming

14. The download a numerical array of how many photons hit each pixel
Number of electrons in each pixel is proportional to the number of photons that hit that pixel. The result is a spreadsheet that is easy to mathematically manipulate.

15. The numbers in the array can be translated to a grayscale

16. Once pixel is assigned a shade of gray, a black & white image is created from the spreadsheet

17. Color imaging requires filters
For pretty pictures we use red, green, blue and luminance. For photometry we use ubvri (Johnson set) or ugriz (SDSS set). Other systems extend into the UV or IR ends of the spectrum

18. It is possible to put filters directly on the CCD chip
All color digital cameras use microfilters. Notice there are more greens than reds or blues. Different chips have different wavelength sensitivity.

19. A color chip has a lower resolution since each “pixel” is actually four
Silicon chips are most sensitive in infrared and red and least sensitive in blue. An infrared filter will cover the entire chip.
The “white balance” adjusts the amplification of each of the colors.

20. A color image download has to account for the colors