― Manual of RGBFisheye.exe―

A application software for automatic calculation of diffuse transmittance

(%PPFD) with hemispherical photographs

2005. 3

Megumi Ishida

Center of Educational research in Field Science,

Gifu Faculty of Applied Biological Science

1-1 Yanagido, Gifu, 501-1193, Japan

http://www.gifu-u.ac.jp/~ishidam/RGBFisheye.htm

e-mail: ishidam@cc.gifu-u.ac.jp

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Index

Summary.........................................................................................................................................2 1.Exposure setting based on the luminance of sky zenith (procedure of AE-Lock method ) ....3

2. How to use RGBFisheye ................................................................................................................4 2-1. Operating requirements..........................................................................................................4 2-2. Selection of image files .........................................................................................................5 2-3. Trimming of the hemispherical photographs ......................................................................5 2-4. Start the calculation .............................................................................................................6 2-5. Save the results of the calculation .......................................................................................6 2-6. Calculation with manual thresholding ................................................................................8 2-7. Menu......................................................................................................................................8 2-8. Trouble shooting .................................................................................................................10

Histograms of pixels are pectinate (comb-like) and calculation results are abnormal. ................10 Spinal noise pattern occurs at the low level of the histograms and calculation results are abnormal...........................................................................................................................................11

Acknowledgements .......................................................................................................................12 References.....................................................................................................................................12

“RGBFisheye.exe” is a application software for automatic calculation of diffuse transmittance

(%PPFD) from digital hemispherical photographs taken with exposure setting based on the

luminance of the zenith of the sky. See accompanying paper about the details of the

automatic thresholding.

ISHIDA M.(2004)Automatic thresholding for digital hemispherical photography. Canadian

Journal of Forest Research: 34(11): 2208-2216

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Summary

Operating procedure 1. Setup of the software (decompress RGBFisheyeSetup.zip and run setup.exe) 2. Execution (run RGBFisheye.exe) 3. Select image files 4. Automatic thresholding Run “>” a image files, “>>” all image files selected 5. Complete the calculation and Save the results（*.csv） *Trimming of the hemispherical photographs are regulated with the coordinates (x,y) of the center and radius of hemi-circle. These values are saved in a configuration file (RGBFisheyeCGF.csv).

Fig. 0-1. Screenshot of RGBFisheye.exe

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1.Exposure setting based on the luminance of sky zenith

(procedure of AE-Lock method )

The exposure was based on the zenith luminance of the sky (Chen, 1991; Clearwater et al., 1999). The procedure with the Nikon Coolpix 950 involves five steps: 1, select Manual-Record Mode; 2, go into Menu; 3, set Metering: Spot; 4, set AE-Lock: Reset; 5, take a photograph with

Fig.1-1. Photography with AE-Lock

1.Set Manual mode、 2.Metering : Spot、3AE-Lock:ON, Reset、4. take a photograph with the lens facing directly up the zenith and set the exposure.

Fig.1-2. Comparison of hemispherical photographs taken with Auto and AE-Lock

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the lens facing directly up the zenith and set the exposure. With this camera, one must take a photograph of the zenith in order to set the exposure with AE-Lock, because one cannot set shutter speed and lens aperture on manual. The photography for the exposure setting needs to be taken in open, canopy gap, and forest edge, because it is necessary that the sky at the zenith is not unobstructed for the metering space. The sampling angle for spot photometry is ca.10 degree with the normal lens.

2. How to use RGBFisheye

2-1. Operating requirements

RGBFisheye was coded with MS Visual Basic ver. 6.0(Japanese) on WindowsXP(Japanese). On setup

procedure with Windows OS of US version, the messages with unreadable characters should be

shown. Nevertheless, the software installed is usable. The software operates on Win32

(Windows 95, 2000 , Me, XP). Windows OS recommended is Windows XP.

Table 2-1. Operating requirements of RGBFisheye

OS Win32 (Windows 2000 , Me, XP) XP recommended

Screen 1024 * 768 pixels or higher indispensableness

Screen color True color (32 bit) indispensableness

Quarity of images

(Nikon Coolpix) Normal or higher indispensableness

On the ordinary setup procedure, following two files are installed under a folder”C:\Program

Files\RGBFisheye”,

RGBFisheye.exe

RGBFisheyeCGF.csv

The former is a execute file, and the later is configuration file including the information

such as directory of image files, and the values for position of a hemicircle.

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2-2. Selection of image files

File > Open Open dialog box “File Open”. RGBFisheye can select a number of image files with left click of a mouse pushing Shift-key or Ctrl-key.

2-3. Trimming of the hemispherical photographs

Trimming of the hemispherical photographs are regulated with the coordinates (x, y) of the

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center and radius (r) of hemi-circle. In order to improve the trimming position, input the value, x, y, or r in textbox of hemicircle, and push return key.

Approximate values is, x = width/2, y = height/2, and r = height/2. The precision values should be determined using the hemispherical photographs of sky with the each condition, such as the camera type. Please note that the maximum zenith angle is not usually 90 degree, for example the angle of Nikkor FC-E8 Nikon is 93 degree. The values of x, y, r are saved in a configuration file (RGBFisheyeCGF.csv), and retained as default values until next alteration.

2-4. Start the calculation

Click the calculation button for automatic thresholding. The image files selected (see 4-2) are calculated one-by-one by ”>” button and continuously by ”>>” button.

2-5. Save the results of the calculation

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File > Save > Analysis results (table) The photography condition and the calculation results are saved in files of “Analysis results (table)”. The column of Diffuse transmittances (%PPFD) is “36.SOC(%)”. Table 2-2. The items saved in the file (default name: DiffusesiteFactor.csv) of calculation results.

Row no. Label Caption

1 No_ sequential serial number

2 file file names

3 Date_Time Date and Time taken photograph

4 fmm focal length

5 F_stop f stop

6 S_Speed shutter speed

7 Sqr(F)/Exp

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9

10

11 Rmean_All mean value of all pixels sampled in Red plane*

12 Gmean_All mean value of all pixels sampled in Green plane*

13 Bmean_All mean value of all pixels sampled in Blue plane*

14 Rmin_All minimum value of all pixels sampled in Red plane*

15 Gmin_All minimum value of all pixels sampled in Green plane*

16 Bmin_All minimum value of all pixels sampled in Blue plane*

17 Rmax_All maximum value of all pixels sampled in Red plane*

18 Gmax_All maximum value of all pixels sampled in Green plane*

19 Bmax_All maximum value of all pixels sampled in Blue plane*

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21 Rmean_Sky mean value of sky pixels sampled in Red plane*

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22 Gmean_Sky mean value of sky pixels sampled in Green plane*

23 Bmean_Sky mean value of sky pixels sampled in Blue plane*

24 Rmin_Sky minimum value of sky pixels sampled in Red plane*

25 Gmin_Sky minimum value of sky pixels sampled in Green plane*

26 Bmin_Sky minimum value of sky pixels sampled in Blue plane*

27 Rmax_Sky maximum value of sky pixels sampled in Red plane*

28 Gmax_Sky maximum value of sky pixels sampled in Green plane*

29 Bmax_Sky maximum value of sky pixels sampled in Blue plane*

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31 Rthreshold threshold of Red plane

32 Gthreshold threshold of Green plane

33 Bthreshold threshold of Blue plane

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35 UOC(%) Diffse transmittance (uniform overcast model)

36 SOC(%) Diffse transmittance (standard overcast model)

37 Area(%) sky(red) area in right analyzed window

*44 632 pixels per hemispherical photographrange (see Ishida 2004)

2-6. Calculation with manual thresholding

RGBFisheye can calculate with manual thresholding on one-by-one image analysis. The threshold values for binary division of hemispherical photographs set with the scroll bars or the text boxes. After the values are changed, the calculation starts in a second.

2-7. Menu

File

Open select image files

Save

Analysis results (table)

Binary (Black & White) image

AutoSave

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RGB pixel values (left window)

Frequency of RGB pixel values

Binary (Black & White) image

Exit

Option

threshold

Maximum curvature

Starting pixel value

Auto level fix

Twilit correct Show sampling area

About

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2-8. Trouble shooting

Histograms of pixels are pectinate (comb-like) and calculation results are abnormal.

The pixel values for each RGB plane must take 8-bits 256 resolutions. Please set the computer screen to true color (32Bit).

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Spinal noise pattern occurs at the low level of the histograms and calculation results are abnormal.

The spinal noise pattern is caused by compression of the image files. The quality of the

photographs (images) must be set “Normal” or higher on the digital camera. Essentially have to calculate the high compression (low quality) image files, adjust a value of the “Starting pixel value” searching the threshold (Option - threshold - Starting pixel value, ordinary about 10).

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Acknowledgements

I wish to thank R.K.Kobe, S.M.Flinn, A. Komiyama, S. Kato, M. Tsukahara, and M.Noguchi, for the valuable comments on the manuscript.

References

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