"colour.convert" definition: sRGB should be the default RGB colorspace, but actually is not?

The documentation for colour.convert states that:

Various defaults have been systematically adopted compared to the low-level Colour API: (…) The default RGB colourspace is the sRGB colourspace. It can also be changed on a per definition basis along the conversion path.

This is my code:

# pip install colour-science networkx
import colour
import numpy as np

np.set_printoptions(suppress=True)

input_rgb = colour.models.eotf_sRGB(np.array([127, 127, 127]) / 255.0)
converted = colour.convert(input_rgb, 'RGB', 'Cie Lab', verbose={'mode': 'Long', 'width': 120})

I assume that this should produce the same output as when changing the last line to

converted = colour.convert(input_rgb, 'sRGB', 'Cie Lab', verbose={'mode': 'Long', 'width': 120})

However, there is a dramatic difference.

This is the output for ‘RGB’:

========================================================================================================================
*                                                                                                                      *
*   [ Conversion Path ]                                                                                                *
*                                                                                                                      *
*   "RGB_to_XYZ" --> "XYZ_to_Lab"                                                                                      *
*                                                                                                                      *
========================================================================================================================
========================================================================================================================
*                                                                                                                      *
*   [ "RGB_to_XYZ" ]                                                                                                   *
*                                                                                                                      *
*   [ Signature ]                                                                                                      *
*                                                                                                                      *
*   <Signature (RGB, illuminant_RGB, illuminant_XYZ, RGB_to_XYZ_matrix, chromatic_adaptation_transform='CAT02',        *
*   cctf_decoding=None, **kwargs)>                                                                                     *
*                                                                                                                      *
*   [ Conversion Output ]                                                                                              *
*                                                                                                                      *
*   [ 0.20172533  0.21223076  0.23111929]                                                                              *
*                                                                                                                      *
========================================================================================================================
========================================================================================================================
*                                                                                                                      *
*   [ "XYZ_to_Lab" ]                                                                                                   *
*                                                                                                                      *
*   [ Signature ]                                                                                                      *
*                                                                                                                      *
*   <Signature (XYZ, illuminant=array([ 0.3127,  0.329 ]))>                                                            *
*                                                                                                                      *
*   [ Conversion Output ]                                                                                              *
*                                                                                                                      *
*   [ 0.53192777  0.0000461   0.00002109]                                                                              *
*                                                                                                                      *
========================================================================================================================

This is the output for ‘sRGB’:

========================================================================================================================
*                                                                                                                      *
*   [ Conversion Path ]                                                                                                *
*                                                                                                                      *
*   "sRGB_to_XYZ" --> "XYZ_to_Lab"                                                                                     *
*                                                                                                                      *
========================================================================================================================
========================================================================================================================
*                                                                                                                      *
*   [ "sRGB_to_XYZ" ]                                                                                                  *
*                                                                                                                      *
*   [ Signature ]                                                                                                      *
*                                                                                                                      *
*   <Signature (RGB, illuminant=array([ 0.3127,  0.329 ]), chromatic_adaptation_method='CAT02',                        *
*   apply_cctf_decoding=True, **kwargs)>                                                                               *
*                                                                                                                      *
*   [ Conversion Output ]                                                                                              *
*                                                                                                                      *
*   [ 0.03521062  0.03704431  0.04034126]                                                                              *
*                                                                                                                      *
========================================================================================================================
========================================================================================================================
*                                                                                                                      *
*   [ "XYZ_to_Lab" ]                                                                                                   *
*                                                                                                                      *
*   [ Signature ]                                                                                                      *
*                                                                                                                      *
*   <Signature (XYZ, illuminant=array([ 0.3127,  0.329 ]))>                                                            *
*                                                                                                                      *
*   [ Conversion Output ]                                                                                              *
*                                                                                                                      *
*   [ 0.22669199  0.00002576  0.00001179]                                                                              *
*                                                                                                                      *
========================================================================================================================

EDIT: This is my environment.

===============================================================================
*                                                                             *
*   Interpreter :                                                             *
*       python : 3.7.8 (tags/v3.7.8:4b47a5b6ba, Jun 28 2020, 08:53:46) [MSC   *
*   v.1916 64 bit (AMD64)]                                                    *
*                                                                             *
*   colour-science.org :                                                      *
*       colour : 0.3.15                                                       *
*                                                                             *
*   Runtime :                                                                 *
*       imageio : 2.9.0                                                       *
*       matplotlib : 3.2.2                                                    *
*       networkx : 2.4                                                        *
*       numpy : 1.19.0                                                        *
*       pandas : 1.0.5                                                        *
*       scipy : 1.5.0                                                         *
*       six : 1.15.0                                                          *
*                                                                             *
===============================================================================

[KelSolaar]

The documentation has been updated: https://colour.readthedocs.io/en/develop/generated/colour.convert.html#colour.convert

[KelSolaar]

Hi @rsnitsch,

Thanks! As you saw the main difference pertains to encoding/decoding in that case, we should make the documentation clearer but besides that, the default IS sRGB, whether it is encoded or not is critical obviously but it does change the fact that the illuminant is D65 and the primaries are that of BT.709/sRGB. We will amend the documentation accordingly, that being said there are hints at that in the notes:

    -   The **RGB** colour representation is assumed to be linear and
        representing *scene-referred* imagery. To convert such *RGB* values to
        *output-referred* (*display-referred*) imagery, i.e. encode the *RGB*
        values using an encoding colour component transfer function
        (Encoding CCTF) / opto-electronic transfer function (OETF / OECF), the
        **Output-Referred RGB** representation must be used.

The graph code is still considered experimental as the warning implies so if you have other issues or misunderstanding, please keep them coming!