Measurement of luminance distributions in the field of ... · Measurement of luminance distributions in the field of view for glare evaluations • Avoid movement in scene (avoid

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

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HDR Cameras

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Reliable glare studies

Reliable luminance measurements

2 different methods• Absolute calibration• ”Self-calibration”

• Automatic algorithm

Glare and luminance

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Absolute HDR camera calibration

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Response curve

The shape of the response curve

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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

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Luminance values calculated based on pixel value, response curve and exposure

HDR generation

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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

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Different programs• PFSTools• hdrgen

• Photosphere• WebHDR

Use up-to-date versions – also of Radiance (current version 5.1)

Automatic algorithm HDR camera calibration

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DSLR camera “self/calibration” procedure

Create LDR images

Create HDR image

Cut images

Calibrate for vignetting

Calibrate for projection

Luminance calibration

Illuminance check

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General camera settings

ISO speed 100White balance DaylightImage quality .JPEG (large)Color space sRGBFocus Infinity (auto off)Picture style Standard

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• Auto bracketing• Computer control

• Manufactures• qDSLRdashboard

General camera setup

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1 EV stop between images

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• 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


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Create LDR images

Create HDR image

Cut images




Illuminance check

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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

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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

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Without –x option

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Check LDR images• Darkest should not have pixels > 200• Whitest should not have pixels < 20

HDR generation

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Response curve

Scene should contain• bright areas• dark areas• white and/or grey areas

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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

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Response curve

Differs for all cameras and apertures

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Create LDR images

Create HDR image

Cut images




Illuminance check

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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

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Create LDR images

Create HDR image

Cut images




Illuminance check

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Vignetting

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Vignetting

Normal camera rotation point

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Vignetting

Nodal rotation point

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Vignetting

Second setup images curtesy of Clotilde Pierson

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Vignetting

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Angle

Aperture – f/11

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Angle

Aperture – f/3.2

Normalized to lens center

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Vignetting

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All apertures

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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

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Apply to images with

pcomb –f [path_to/vignetting.cal] –o [original_image.hdr] > [corrected_image.hdr]

VignettingCal file example

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Vignetting

• Canon 70D • Sigma 4.5mm f/2.8 fisheye lens

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Create LDR images

Create HDR image

Cut images




Illuminance check

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Projection

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Projection

180 px133 px

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From Sigma:

Projection

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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]

https://www.radiance-online.org/cgi-bin/viewcvs.cgi/ray/src/cal/cal/

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Also make sure the fisheye lens fits the sensor frame

Projection

Sensor frame

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Also make sure the fisheye lens fits the sensor frame

Projection

Sensor frame

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Create LDR images

Create HDR image

Cut images




Illuminance check

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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 %

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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 %

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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)

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Create LDR images

Create HDR image

Cut images




Illuminance check

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Measure illuminance in scene

Calculate from HDR image

Illuminance check

LMT Image Factor1150 1145,8 1,004

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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

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High luminance scenes

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Be careful - long exposures with very high luminance can “burn out” the image sensor


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Use filters to reduce light on sensor


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30 sec exposure at f/11

However, filters raises other problems

Grainy HDR

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6 layers of 0,3 filters on window


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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

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Konica Minolta: 1: 1.674.000 cd/m2

2: 275 cd/m2

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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

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Konica Minolta: 1: 261.000 cd/m2

2: 313 cd/m2

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Avoid very high luminancesCheck that the recorded values are correct

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Other

Avoid flicker• Influences pixel values

R: 148G: 162B: 189

R: 159G: 181B: 203

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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

https://www.radiance-online.org/community/mailing-lists

Documents

Measurement of luminance distributions in the field of ... · Measurement of luminance distributions in the field of view for glare evaluations • Avoid movement in scene (avoid