Reflectance Data (original) (raw)

Welcome to our main repository of reflectance data. Most of our BRDF data were measured using our custom-built gonioreflectometer. For each pair of incident and reflection directions, we measured two polarizations. The polarized measurements are combined into unpolarized data to account for the polarization bias of the setup. The 1024 original wavelength samples are filtered down to 65 or 31 wavelengths, with 5 or 10nm intervals between 400 and 700nm. Note that the measurements are noisy at short wavelengths and for grazing angles, where the signal is weak. For smooth surfaces, the specular reflection causes a spike in the mirror directions, which is not necessarily an accurate representation of this peak.

Some data sets were acquired via our image-based measurement technique, using a digital camera. These datasets containt only red, green, and blue channels; data on source and camera spectra are supplied with each to aid in calibration. In general, the RGB triples do not share geometry, as they are individual sensels in a Bayer array.

Painted Surfaces

We have measured the full BRDF of several painted surfaces. These are divided into several categories:

Automotive Paints used to paint cars and other motor vehicles. Thanks to Ford Motor Company for providing the test samples.
Spray Paints available in aerosol cans. These have lower gloss than the car paints.
House Paints that you might buy and brush on your wall.

Human Skin

Human Skin measured by our image-based measurement technique.

Other Surfaces

Ceramics including an unglazed clay flowerpot.
Other Surfaces measured by our gonioreflectometer.

Data File Formats

Gonioreflectometer Data

All gonioreflectometer data are available in MATLAB binary files. In addition, these data are available in a more readable text format.

We have also calculated tristimulus values in CIE XYZ space from the spectral data; they were calculated for the surface illuminated with a D65 illuminant; this should work well if your monitor is set to a D65 white point. That is to say, an ideal white surface illuminated by a source that is equal in all three channels will result in equal RGB on the monitor.

Finally, we used the XYZ tristimulus values to calculate RGB values for Sony Trinitron phosphors. NOTE: No attempt has been made to fit the BRDF values into the monitor gamut: there are negative values in the RGB files. You must decide what best to do to display the colors on your monitor.

ASTM Standard E1392-96

This format is intended to comply with ASTM Standard E1392-96, available from the American Society for Testing and Materials for 20−20-20−30. The important parts of the file are the line starting VARS which lists the variables actually contained in the file: (theta_i,phi_i) for the incident elevation and azimuth angles, respectively, (theta_s,phi_s) for the corresponding exitant (scattering) angles, and the BRDF values at the specified wavelengths. These either are actual measurements at equally-spaced wavelengths or tristimulus values in CIE XYZ space or RGB space for Sony Trinitron phosphors.

NOTE: We have no way to test compliance with the ASTM standard, as we know of no software which reads this format, nor have we found any sample data files. If these files do not comply with the standard, please let us know, as we want to comply with a known standard for storing and disseminating BRDF information.

MATLAB files

Many data are available in .mat files; these are binary files that can be read by MATLAB, software available fromMathWorks. Many of these data are also available in other formats.

Image-Based Data: Binary files

The BRDF data are in separate files for red, green, and blue channels. These files are named..{rgb}.data, where is a file name used to label the data is the frame number of a source image{rgb} is r for the red channel, g for the green channel, and b for the blue channel. Each file contains binary IEEE-754 floating-point values, big-endian, with 6 values for each point:

X and Y components of the incident vector,
X and Y components of the exitant (viewing) vector,
computed irradiance, and
computed exitant radiance. The two vectors are defined in a reference frame where the surface normal is in the Z direction. Because these are isotropic measurements, the orientation of the X and Y axes in the tangent plane is arbitrary. The BRDF value is simply the exitant radiance divided by the incident irradiance. Note: these quantities are not calibrated to any actual radiometric units; only their ratio is meaningful.

Other data: Spectrum Files

Files with an extension of .spc are ASCII files with spectrum information. In general, there will be several lines of annotation data, followed by one line per wavelength containing the wavelength (in nanometers) and the value for that wavelength. Files may contain more than one spectrum, e.g. for the RGB response curves of a camera.