Measurement of luminance distributions in the field of view for glare evaluations
Jan Wienold & Peter HansenInterdisciplinary Laboratory of Performance-Integrated Design (LIPID)Ecole polytechnique fédérale de Lausanne (EPFL)
WORKSHOPMeasurement of luminance distributions in the field of view for glare evaluations
1 | PH | 10.2017
HDR Cameras
2 | PH | 23-10.2017
Measurement of luminance distributions in the field of view for glare evaluations
Reliable glare studies
Reliable luminance measurements
2 different methods• Absolute calibration• ”Self-calibration”
• Automatic algorithm
Glare and luminance
3 | PH | 23-10.2017
Measurement of luminance distributions in the field of view for glare evaluations
Absolute HDR camera calibration
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Response curve
The shape of the response curve
4 | PH | 23-10.2017
Measurement of luminance distributions in the field of view for glare evaluations
Absolute HDR camera calibration
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Exposure 1
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Exposure 2
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Exposure ...
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Exposure ...
For each aperture know at least one luminance value
5 | PH | 23-10.2017
Measurement of luminance distributions in the field of view for glare evaluations
Luminance values calculated based on pixel value, response curve and exposure
HDR generation
6 | PH | 23-10.2017
Measurement of luminance distributions in the field of view for glare evaluations
Automatic algorithm HDR camera calibration
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Pixel value
Response curve
20 < 𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃 𝑉𝑉𝑉𝑉𝑃𝑃𝑉𝑉𝑃𝑃 < 200
An automatic calibration algorithm is used to derive a response curve
7 | PH | 23-10.2017
Measurement of luminance distributions in the field of view for glare evaluations
Different programs• PFSTools• hdrgen
• Photosphere• WebHDR
Use up-to-date versions – also of Radiance (current version 5.1)
Automatic algorithm HDR camera calibration
8 | PH | 23-10.2017
Measurement of luminance distributions in the field of view for glare evaluations
DSLR camera “self/calibration” procedure
Create LDR images
Create HDR image
Cut images
Calibrate for vignetting
Calibrate for projection
Luminance calibration
Illuminance check
9 | PH | 23-10.2017
Measurement of luminance distributions in the field of view for glare evaluations
General camera settings
ISO speed 100White balance DaylightImage quality .JPEG (large)Color space sRGBFocus Infinity (auto off)Picture style Standard
10 | PH | 23-10.2017
Measurement of luminance distributions in the field of view for glare evaluations
• Auto bracketing• Computer control
• Manufactures• qDSLRdashboard
General camera setup
11 | PH | 23-10.2017
Measurement of luminance distributions in the field of view for glare evaluations
General camera setup
1 EV stop between images
12 | PH | 23-10.2017
Measurement of luminance distributions in the field of view for glare evaluations
• Avoid movement in scene (avoid ghosting)• Avoid shaking camera• Use a tripod• Use a computer for bracketing • Black to white image series• Use targets in the scene
• High luminance• Low luminance
• Measure vertical illuminance
General camera setup
13 | PH | 23-10.2017
Measurement of luminance distributions in the field of view for glare evaluations
DSLR camera “self/calibration” procedure
Create LDR images
Create HDR image
Cut images
Calibrate for vignetting
Calibrate for projection
Luminance calibration
Illuminance check
14 | PH | 23-10.2017
Measurement of luminance distributions in the field of view for glare evaluations
Generate HDR hgrgen –o –r –a –e –f –g –x
‒ o = output file‒ r = response curve file‒ a = automatic exposure alignment‒ e = exposure adjustment ‒ f = flare removal‒ g = ghost removal‒ x = over and under exposure removal
HDR generation
15 | PH | 23-10.2017
Measurement of luminance distributions in the field of view for glare evaluations
HDR generation
1: 89.809 cd/m2
2: 291 cd/m21: 2.653.980 cd/m2
2: 281 cd/m2
With –x option
Konica Minolta: 1: 1.674.000 cd/m2
2: 275 cd/m2
12 12
Without –x option
16 | PH | 23-10.2017
Measurement of luminance distributions in the field of view for glare evaluations
Check LDR images• Darkest should not have pixels > 200• Whitest should not have pixels < 20
HDR generation
17 | PH | 23-10.2017
Measurement of luminance distributions in the field of view for glare evaluations
Response curve
Scene should contain• bright areas• dark areas• white and/or grey areas
18 | PH | 23-10.2017
Measurement of luminance distributions in the field of view for glare evaluations
hgrgen –o –r –a –e –f –g to generate HDR and curve
With –r option give name to response curve fileSave it and use it to make HDR images
[n] degree polynomial
Response curve – HDR generation
19 | PH | 23-10.2017
Measurement of luminance distributions in the field of view for glare evaluations
Response curve
Differs for all cameras and apertures
20 | PH | 23-10.2017
Measurement of luminance distributions in the field of view for glare evaluations
DSLR camera “self/calibration” procedure
Create LDR images
Create HDR image
Cut images
Calibrate for vignetting
Calibrate for projection
Luminance calibration
Illuminance check
21 | PH | 23-10.2017
Measurement of luminance distributions in the field of view for glare evaluations
Cut HDR image
pcompos -x [x-max] -y [y-max] -h [org_image.hdr] -[x-min] –[y-min] > [cut_image.hdr]
x-maxx-miny-max
y-min
22 | PH | 23-10.2017
Measurement of luminance distributions in the field of view for glare evaluations
DSLR camera “self/calibration” procedure
Create LDR images
Create HDR image
Cut images
Calibrate for vignetting
Calibrate for projection
Luminance calibration
Illuminance check
23 | PH | 23-10.2017
Measurement of luminance distributions in the field of view for glare evaluations
Vignetting
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24 | PH | 23-10.2017
Measurement of luminance distributions in the field of view for glare evaluations
Vignetting
Normal camera rotation point
25 | PH | 23-10.2017
Measurement of luminance distributions in the field of view for glare evaluations
Vignetting
Nodal rotation point
26 | PH | 23-10.2017
Measurement of luminance distributions in the field of view for glare evaluations
Vignetting
Second setup images curtesy of Clotilde Pierson
27 | PH | 23-10.2017
Measurement of luminance distributions in the field of view for glare evaluations
Vignetting
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Angle
Aperture – f/11
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Angle
Aperture – f/3.2
Normalized to lens center
28 | PH | 23-10.2017
Measurement of luminance distributions in the field of view for glare evaluations
Vignetting
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Angle
All apertures
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29 | PH | 23-10.2017
Measurement of luminance distributions in the field of view for glare evaluations
Create a .cal file with the polynomial equation
Vignetting
y = -3,771557x6 + 2,658279x5 + 6,604217x4 - 8,870208x3 + 3,430605x2 - 0,474940x + 1,001537R² = 0,995700
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Relative angle
Aperture –f/3.2
Establish 6th order polynomial for vignetting curve
30 | PH | 23-10.2017
Measurement of luminance distributions in the field of view for glare evaluations
Apply to images with
pcomb –f [path_to/vignetting.cal] –o [original_image.hdr] > [corrected_image.hdr]
VignettingCal file example
31 | PH | 23-10.2017
Measurement of luminance distributions in the field of view for glare evaluations
Vignetting
• Canon 70D • Sigma 4.5mm f/2.8 fisheye lens
32 | PH | 23-10.2017
Measurement of luminance distributions in the field of view for glare evaluations
DSLR camera “self/calibration” procedure
Create LDR images
Create HDR image
Cut images
Calibrate for vignetting
Calibrate for projection
Luminance calibration
Illuminance check
33 | PH | 23-10.2017
Measurement of luminance distributions in the field of view for glare evaluations
Projection
34 | PH | 23-10.2017
Measurement of luminance distributions in the field of view for glare evaluations
Projection
180 px133 px
35 | PH | 23-10.2017
Measurement of luminance distributions in the field of view for glare evaluations
From Sigma:
Projection
36 | PH | 23-10.2017
Measurement of luminance distributions in the field of view for glare evaluations
Fisheye correction file from: https://www.radiance-online.org/cgi-bin/viewcvs.cgi/ray/src/cal/cal/
Projection
fisheye_corr.cal
pcomb –f [path_to/fisheye_corr.cal] -o [original_image.hdr] > [corrected_image.hdr]
37 | PH | 23-10.2017
Measurement of luminance distributions in the field of view for glare evaluations
Also make sure the fisheye lens fits the sensor frame
Projection
Sensor frame
38 | PH | 23-10.2017
Measurement of luminance distributions in the field of view for glare evaluations
Also make sure the fisheye lens fits the sensor frame
Projection
Sensor frame
39 | PH | 23-10.2017
Measurement of luminance distributions in the field of view for glare evaluations
DSLR camera “self/calibration” procedure
Create LDR images
Create HDR image
Cut images
Calibrate for vignetting
Calibrate for projection
Luminance calibration
Illuminance check
40 | PH | 23-10.2017
Measurement of luminance distributions in the field of view for glare evaluations
Luminance adjustment
Target Konica Image Factor1 151 140,2 1,0772 268 247,2 1,0843 107 98,5 1,086
pcomb -s 1.08 -o [original_image.hdr] > [adjusted_image.hdr]
Should be less than ± 20 %
41 | PH | 23-10.2017
Measurement of luminance distributions in the field of view for glare evaluations
Luminance adjustment
Target Konica Image Factor1 151 151,1 0,9992 268 266,2 1,0073 107 107,8 0,993
pcomb -s 1.08 -o [original_image.hdr] > [adjusted_image.hdr]
Should be less than ± 20 %
42 | PH | 23-10.2017
Measurement of luminance distributions in the field of view for glare evaluations
Check header
Remove or reset exposure to 1
Set “View” string to the right values (no “tab” in front)-vta –vh 180 –vv 180
Remember to use the current version of Radiance (5.1 at the moment)
43 | PH | 23-10.2017
Measurement of luminance distributions in the field of view for glare evaluations
DSLR camera “self/calibration” procedure
Create LDR images
Create HDR image
Cut images
Calibrate for vignetting
Calibrate for projection
Luminance calibration
Illuminance check
44 | PH | 23-10.2017
Measurement of luminance distributions in the field of view for glare evaluations
Measure illuminance in scene
Calculate from HDR image
Illuminance check
LMT Image Factor1150 1145,8 1,004
45 | PH | 23-10.2017
Measurement of luminance distributions in the field of view for glare evaluations
Do NOT use this to adjust luminance
This is a check that the “energy balance” of the image is correct
± 10 % is okay but should be random
Illuminance check
46 | PH | 23-10.2017
Measurement of luminance distributions in the field of view for glare evaluations
High luminance scenes
47 | PH | 23-10.2017
Measurement of luminance distributions in the field of view for glare evaluations
Be careful - long exposures with very high luminance can “burn out” the image sensor
High luminance scenes
48 | PH | 23-10.2017
Measurement of luminance distributions in the field of view for glare evaluations
Use filters to reduce light on sensor
High luminance scenes
49 | PH | 23-10.2017
Measurement of luminance distributions in the field of view for glare evaluations
High luminance scenes
30 sec exposure at f/11
However, filters raises other problems
Grainy HDR
50 | PH | 23-10.2017
Measurement of luminance distributions in the field of view for glare evaluations
6 layers of 0,3 filters on window
High luminance scenes
51 | PH | 23-10.2017
Measurement of luminance distributions in the field of view for glare evaluations
6 layers of 0,3 filters on window
High luminance scenes
1: 1.651.000 cd/m2
2: 274 cd/m21: 762.973 cd/m2
2: 12.110 cd/m21: 2.653.980 cd/m2
2: 281 cd/m2
Canon 0.1 % filter TechnoTeam 0.01 % filter Canon no filter
12 2 12 1
Konica Minolta: 1: 1.674.000 cd/m2
2: 275 cd/m2
52 | PH | 23-10.2017
Measurement of luminance distributions in the field of view for glare evaluations
8 layers of 0,3 filters on window
High luminance scenes
1: 264.000 cd/m2
2: 327 cd/m21: 342.192 cd/m2
2: 28.125 cd/m21: 388.479 cd/m2
2: 350 cd/m2
Canon 0.1 % filter TechnoTeam 0.01 % filter Canon no filter
12 2 12 1
Konica Minolta: 1: 261.000 cd/m2
2: 313 cd/m2
53 | PH | 23-10.2017
Measurement of luminance distributions in the field of view for glare evaluations
High luminance scenes
Avoid very high luminancesCheck that the recorded values are correct
54 | PH | 23-10.2017
Measurement of luminance distributions in the field of view for glare evaluations
Other
Avoid flicker• Influences pixel values
R: 148G: 162B: 189
R: 159G: 181B: 203
55 | PH | 23-10.2017
Measurement of luminance distributions in the field of view for glare evaluations
When “self-calibrating”• Use recommended camera settings• Use a tripod• Create good response curves• Correct for vignetting• Correct for projection• Luminance adjust • Check vertical illuminance• Check the header• Be careful with very high luminance
Use the forums; Radiance HDRI is a good starthttps://www.radiance-online.org/community/mailing-lists
Synthesis
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