Spectral Representation and Interchange

[thomasmansencal]

Hello,

Starting a thread to talk about spectral representation and interchange, there is not a lot of software besides research related one that uses spectrally defined data but having a standard representation for the M&E industry will help adoption. Having spent a bit of time in that space the past decade, the two obvious candidates for that are:

• An OpenEXR Layout for Spectral Images
• CxF

Keen to hear people thoughts!

[scoopxyz]

I would also be interested in seeing what is appropriate for our industry.

The remote sensing industry is another sector where multi/hyper-spectral data is frequently used and shared. Some formats there to use as reference:

• ENVI Image
• HDF5 - less standardized, but widely used

Its also worth mentioning iccMAX which does support spectral use cases and BRDF descriptions. Though its adoption has not been widespread.

In theory the format would need to be quite flexible as there are a variety of potential spectral data:

• Single Spectral Measurement
• Collection of Single Spectral Measurements (no spatial dimension)
• Spectral Hypercube (spatial dimension)
• ? Spectral BxDF (angular dimension) ?

I'm not seeing a present solution that solves all of these.

[thomasmansencal]

Thanks @scoopxyz,

Those are good to consider too!

The Spectral BxDF could technically be represented in any format having multi-dimensionality and the Fichet et al. (2021) OpenEXR layout could do that trivially however, a naive implementation would result in some catastrophic increase in file size. It already support bi-spectral representation, e.g., fluorescense, and for a given wavelength, you might have an arbitrary number of emission wavelengths:

exrinfo /Users/kelsolaar/Downloads/sample-images/BiSpectral.exr
File '/Users/kelsolaar/Downloads/sample-images/BiSpectral.exr':
  compression: 'zip'
  displayWindow: [ 0, 0 - 149 149 ] 150 x 150
  dataWindow: [ 0, 0 - 149 149 ] 150 x 150
  channels: 864 channels
   'B': float samp 1 1
   'G': float samp 1 1
   'R': float samp 1 1
   'T.380,000000nm': float samp 1 1
   'T.380,000000nm.390,000000nm': float samp 1 1
   'T.380,000000nm.400,000000nm': float samp 1 1
   'T.380,000000nm.410,000000nm': float samp 1 1
   'T.380,000000nm.420,000000nm': float samp 1 1
   'T.380,000000nm.430,000000nm': float samp 1 1
   'T.380,000000nm.440,000000nm': float samp 1 1
   'T.380,000000nm.450,000000nm': float samp 1 1
   'T.380,000000nm.460,000000nm': float samp 1 1
   'T.380,000000nm.470,000000nm': float samp 1 1
   'T.380,000000nm.480,000000nm': float samp 1 1
   'T.380,000000nm.490,000000nm': float samp 1 1
   'T.380,000000nm.500,000000nm': float samp 1 1
   'T.380,000000nm.510,000000nm': float samp 1 1
   'T.380,000000nm.520,000000nm': float samp 1 1
   'T.380,000000nm.530,000000nm': float samp 1 1
   'T.380,000000nm.540,000000nm': float samp 1 1
   'T.380,000000nm.550,000000nm': float samp 1 1
   'T.380,000000nm.560,000000nm': float samp 1 1
   'T.380,000000nm.570,000000nm': float samp 1 1
   'T.380,000000nm.580,000000nm': float samp 1 1
   'T.380,000000nm.590,000000nm': float samp 1 1
   'T.380,000000nm.600,000000nm': float samp 1 1
   'T.380,000000nm.610,000000nm': float samp 1 1
   'T.380,000000nm.620,000000nm': float samp 1 1
   'T.380,000000nm.630,000000nm': float samp 1 1
   'T.380,000000nm.640,000000nm': float samp 1 1
   'T.380,000000nm.650,000000nm': float samp 1 1
   'T.380,000000nm.660,000000nm': float samp 1 1
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   'T.380,000000nm.680,000000nm': float samp 1 1
   'T.380,000000nm.690,000000nm': float samp 1 1
   'T.380,000000nm.700,000000nm': float samp 1 1
   'T.380,000000nm.710,000000nm': float samp 1 1
   'T.380,000000nm.720,000000nm': float samp 1 1
   'T.380,000000nm.730,000000nm': float samp 1 1
   'T.380,000000nm.740,000000nm': float samp 1 1
   'T.380,000000nm.750,000000nm': float samp 1 1
   'T.380,000000nm.760,000000nm': float samp 1 1
   'T.380,000000nm.770,000000nm': float samp 1 1
   'T.380,000000nm.780,000000nm': float samp 1 1
   'T.390,000000nm': float samp 1 1
   'T.390,000000nm.400,000000nm': float samp 1 1
   'T.390,000000nm.410,000000nm': float samp 1 1
   'T.390,000000nm.420,000000nm': float samp 1 1
   'T.390,000000nm.430,000000nm': float samp 1 1
   'T.390,000000nm.440,000000nm': float samp 1 1
   'T.390,000000nm.450,000000nm': float samp 1 1
   'T.390,000000nm.460,000000nm': float samp 1 1
   'T.390,000000nm.470,000000nm': float samp 1 1
   'T.390,000000nm.480,000000nm': float samp 1 1
   'T.390,000000nm.490,000000nm': float samp 1 1
   'T.390,000000nm.500,000000nm': float samp 1 1
   'T.390,000000nm.510,000000nm': float samp 1 1
   'T.390,000000nm.520,000000nm': float samp 1 1
   'T.390,000000nm.530,000000nm': float samp 1 1
   'T.390,000000nm.540,000000nm': float samp 1 1
   'T.390,000000nm.550,000000nm': float samp 1 1
   'T.390,000000nm.560,000000nm': float samp 1 1
   'T.390,000000nm.570,000000nm': float samp 1 1
   'T.390,000000nm.580,000000nm': float samp 1 1
   'T.390,000000nm.590,000000nm': float samp 1 1
   'T.390,000000nm.600,000000nm': float samp 1 1
   'T.390,000000nm.610,000000nm': float samp 1 1
   'T.390,000000nm.620,000000nm': float samp 1 1
   'T.390,000000nm.630,000000nm': float samp 1 1
   'T.390,000000nm.640,000000nm': float samp 1 1
   'T.390,000000nm.650,000000nm': float samp 1 1
   'T.390,000000nm.660,000000nm': float samp 1 1
   'T.390,000000nm.670,000000nm': float samp 1 1
   'T.390,000000nm.680,000000nm': float samp 1 1
   'T.390,000000nm.690,000000nm': float samp 1 1
   'T.390,000000nm.700,000000nm': float samp 1 1
   'T.390,000000nm.710,000000nm': float samp 1 1
   'T.390,000000nm.720,000000nm': float samp 1 1
   'T.390,000000nm.730,000000nm': float samp 1 1
   'T.390,000000nm.740,000000nm': float samp 1 1
   'T.390,000000nm.750,000000nm': float samp 1 1
   'T.390,000000nm.760,000000nm': float samp 1 1
   'T.390,000000nm.770,000000nm': float samp 1 1
   'T.390,000000nm.780,000000nm': float samp 1 1
[...]
   'T.750,000000nm': float samp 1 1
   'T.750,000000nm.760,000000nm': float samp 1 1
   'T.750,000000nm.770,000000nm': float samp 1 1
   'T.750,000000nm.780,000000nm': float samp 1 1
   'T.760,000000nm': float samp 1 1
   'T.760,000000nm.770,000000nm': float samp 1 1
   'T.760,000000nm.780,000000nm': float samp 1 1
   'T.770,000000nm': float samp 1 1
   'T.770,000000nm.780,000000nm': float samp 1 1
   'T.780,000000nm': float samp 1 1

[thomasmansencal]

For what its worth, I have rolled Fichet et al. (2021) support into Colour: colour-science/colour#1261