1. Noise Reduction in Digital Images Lana Jobes Research Advisor: Dr. Jeff Pelz

2. Chart 2 of 21 Lana Jobes Introduction Long Exposure Times are a Problem with CCD Arrays - Objectionable Noise Present in Images Caused by Thermal Excitation in Camera Electronics - Noise is Additive and Band Dependent Research Has Developed Technique to Reduce This Noise

3. Chart 3 of 21 Lana Jobes Introduction Kodak Recommends Using Exposure Times Less than 1/4 Second -Applies to High-End and Low-end Cameras Image Noise Increases Dramatically with Long Exposure Times Limits Usage in Low-Light Situations and Limits Effective Sensitivity

4. Chart 4 of 21 Lana Jobes Methods Characterization of the Noise - 48 ‘Dark’ Images Obtained Using Kodak DCS 315 Camera - 12 Different Exposure Times Ranging 1/6 to 30 Seconds - 2 Images per Exposure Time on 2 Different Days - Lens Cap On to Isolate Noise

5. 30 Second Exposure Time

6. 30 Second Exposure15 Second Exposure

7. Chart 7 of 21 Lana Jobes Methods Identification of ‘Hot’ pixels - Histograms of Each Color Channel - Thresholds Chosen for Each Band Red -- 40 Green -- 30 Blue -- 60 - Number of Hot Pixels > Threshold Red -- 113,328 (7%) Green -- 62,970 (4%) Blue -- 135,949 (9%)

8. Chart 8 of 21 Lana Jobes Methods First Attempt to Reduce the Noise - For Each ‘Hot’ Pixel, Located a ‘Cold’ One 05101550 5510202040 205651035 1515251545 1040352050 0123401234 0 4 3 2 1 - Created File Containing x,y Coordinates for Hot (2,2) and Cold Pixels (0,0) - Process Images Substituting ‘Cold’ Value for ‘Hot’ One

9. Edge Artifact Discovered Original Image Processed Image

10. Chart 10 of 21 Lana Jobes Methods Second Attempt to Reduce the Noise - Selective Median Filtering for ‘Hot’ Pixels - Sort Surrounding Pixels Within a Specified Radius - Replace ‘Hot’ Pixel with Median Value 013101018 010101312 012651110 010101510 011102010 0,0,0,0,0,10,10,10,10,10,10,10,10,10,10,11,11,12,12,13,13,15,18,20,65 Median Value

11. Chart 11 of 21 Lana Jobes Methods Determine Best Width or Radius for Filtering - Noise in Green Channel Mostly Single Pixels - Noise in Blue and Red in Clusters - Decided to Use Channel Dependent Widths 3x3 for Green 7x7 for Red 11x11 for Blue

12. Image Before Processing Image After Processing with Selective Median Filter

13. Original Image First Method Median Filtered

14. Chart 14 of 21 Lana Jobes Methods Transformation to CIE L*a*b* Color Space - CIE L*a*b* is a Uniform Color Space Models Human Visual System - ‘L*’ - Luminance Information - ‘a*’ - Red/Green Information - ‘b*’ - Yellow/Blue Information

15. Chart 15 of 21 Lana Jobes Methods Amount of Filtering Channel Dependent - Light Filtering in L* Channel Main Contributer to Sharpness Perception Use Filter Radius of 1 Pixel Filter 5% of Pixels - Moderate Filtering in a* Channel Small ‘Clumps’ of Noise Use Filter Radius of 4 Pixels Filter 15% of Pixels

16. Chart 16 of 21 Lana Jobes Methods Amount of Filtering Channel Dependent (con’t) - Aggressive Filtering in b* Channel Large ‘Clumps’ of Noise Use Filter Radius of 6 Pixels Filter Entire Channel

17. Image After Processing in RGB Space Image After Processing in CIE L*a*b* Space

18. Original Image Image After Processing in CIE L*a*b* Space

19. Image After Processing in RGB Space Image After Processing in CIE L*a*b* Space

20. Image After Processing in RGB Space Image After Processing in CIE L*a*b* Space

21. Chart 21 of 21 Lana Jobes Conclusion Technique Developed That Significantly Reduces Additive Noise - Use of Color Space Transformation - Channel Dependent Noise Reduction Further Refinements Still Underway Patent Pending