Are there "LAB2Spectral" and "Spectral2LAB" functions?

[ademmler]

Hi there,

I am reading the documentation and I am woundering if there is functions for:
LAB2Spectral and Spectral2LAB computation?

[KelSolaar]

Hi @ademmler,

We do not have such functions but we have spectral to XYZ (colour.sd_to_XYZ) and XYZ to spectral (colour.XYZ_to_sd). From there you can got to CIE Lab at both ends. Let us know how it goes!

Cheers,

Thomas

[ademmler]

Hi Thomas, thx for the hint.

I am new to Python and Colour but I have created a first trial - see below.
All comments are more than welcome.

#----------------- first trial ------------------------------------#
import numpy as np
import colour
from colour import MSDS_CMFS, SDS_ILLUMINANTS, SpectralShape,SpectralDistribution
from colour.colorimetry import sd_to_XYZ_integration
from colour.utilities import numpy_print_options
from colour.plotting import *

PLOT = True

#Set a view thigs first
np.set_printoptions(suppress=True, precision=4)

# Define the LAB values
Lab_values = np.array([90, 10, 50])
print("Input LAB values:", Lab_values)

# Convert LAB to Spectral
XYZ_values = colour.Lab_to_XYZ(Lab_values)
cmfs = (
    MSDS_CMFS["CIE 1931 2 Degree Standard Observer"]
    .copy()
    .align(SpectralShape(400, 700, 10))
)
illuminant = SDS_ILLUMINANTS["D50"].copy().align(cmfs.shape)
sd = colour.XYZ_to_sd(
    XYZ_values, method="Jakob 2019", cmfs=cmfs, illuminant=illuminant
)

# Convert Spectral to LAB
XYZ_values2 = colour.sd_to_XYZ(sd, cmfs, illuminant, use_practice_range=False)
#print("Output XYZ values:", XYZ_values2/100)

Lab_values2 = colour.XYZ_to_Lab(XYZ_values2/100)
print("Output LAB values:", Lab_values2)

if PLOT:
    print("Spectral values:", sd)
    plot_single_sd(sd)

[KelSolaar]

It seems to work!

Btw, if you enclose your code as follows in Github you should have syntax highlighting:

```python
foo = bar
```

[ademmler]

Thx for you hint about GH!

Which method for XYZ_to_sd would you recommend to do a round trip Lab -> XYZ -> SD -> XYZ -> Lab