1. WHITE REFLECTANCE STANDARD SOL MARIE CRUZ RIVERA September 19,2006 INEL6088

2. WHAT IS WHITE? An object can be called “white” when, for all the colors (wavelengths) of the visible spectrum, 100% of the light shining on the object is reflectively diffused.

3. REFLECTIVELY DIFFUSED Diffused Ideal White Reflectively diffused mean that light is reflected back uniformly in all directions.

4. WHITE REFLECTANCE STANDARD 99% Ideal for Calibration and Standardization Durable and Waterproof Highly Diffuse and Lambertian Consistent Reflectance Over Time Thermally Stable Specifications:  Overall Dimensions: 1.50” Dia. x 0.55”T  Reflectance Area: 1.25” Dia.  Max. Operating Temp.: 400°C  Diffuse Reflection Std: ±4% over 200-2500nm

5. CALIBRATE AN IMAGE – VALUE OF THE CORRECTED PIXEL Average value of the white reflectance target Average value of the black target Value of a specific pixel of the reference image. 0 255

6. HOW TO CALIBRATE AN IMAGE USING THE WHITE REFLECTANCE STANDARD Take an image of the white reflectance standard and a black object. Take the average of the pixels of the white reflectance standard. Take the average of the pixels of the black object. Subtract the average of the pixels of the black object to all the pixels of the Reference Image. Multiply all the pixels of the resultant image by the ratio :

7. REFERENCE IMAGE Figure 1: Reference Image

8. HISTOGRAM REF. IMAGE Figure 2: Histogram of the Reference Image

9. AVERAGE VALUES-REF.IMAGE

10. CALIBRATED IMAGE Figure 3: Calibrated Image

11. HIST CORRECTED IMAGE Figure 4: Histogram of the Corrected Image

12. AVERAGE VALUES-NEW.IMAGE

13. REAL vs. CORRECTED IMAGE The white is more brilliant in the corrected image.

14. UNDERSTANDING WHITE BALANCE – DIGITAL WORLD We can use filters to correct for incandescent or fluorescent lighting. In the digital world these correction filters are replaced by a feature called “White Balance”.

15. WHITE BALANCE The purpose of the WB is to make sure that the imaged white corresponds to the required white

16. LIGHT COLOUR TEMPERATURE The reason that pictures turn out with a yellow/orange cast in incandescent (tungsten) lighting and bluish in fluorescent lighting is because light has a colour temperature. Low colour temp shifts light toward the red. A high colour temp shifts light toward the blue. Different light sources emit light at different colour temperatures.

17. MANUAL WHITE BALANCE Tell the camera which object in the room is white and supposed to come out white in the picture. Point to a white object, filling the screen completely with it. The camera calculate the difference between the current colour temperature of that object and the correct colour temperature of a white object. Then shift all colours by that difference.

18. PRESET WHITE BALANCE Cameras provide preset white balance settings such as: Tungsten, Fluorescent, Cloudy, Sunny, etc. Preset WB can improve the image specially under indoors lighting.

19. AUTO WHITE BALANCE Selected by default Appropriate for general snapshots, and where the illumination is principally from a single type. AWB works very well in sunny and cloudy outdoors. Works fine for most indoors situations.

20. EXAMPLES Auto White BalancePreset White Balance - Tungsten Indoor lighting: two incandescent (tungsten) bulbs. By a preset Tungsten WB, the image gives a truer representation of the scene. Fan is really white.

21. © Danny Pascale and The Babel Color Company

22. REFERENCES [1]Edmund Optics, 2005 Optics and Optical Instruments Catalog [2] http://www.gigahertzoptik.com [3] http://www.photoxels.com/tutorial_white- balance.html [4] http://www.BabelColor.com