[Rd] [FORGED] grDevices::convertColor and colorRamp(space='Lab') Performance Improvements

[Paul Murrell]

Thanks Brodie.  Having a look at all of this is on my list.

Paul

On 03/10/18 14:13, Brodie Gaslam via R-devel wrote:
> `grDevices::convertColor` performance can be improved by 30-300x with 
> small changes to the code.  `colorRamp(space='Lab')` uses `convertColor` 
> so it too benefits from substantial performance gains.
> 
> `convertColor` vectorizes explicitly over the rows of the input color 
> matrix using `apply`. The level-1 patch [1] illustrates a possible 
> minimal set of changes to achieve this with just R matrix and vector 
> operations.  The changes consist primarily of switching `if/else` to 
> `ifelse`, `c` to `cbind`, `sum` to `rowSums`, etc. This results in 
> speedups of 30-100x as shown in table 1:
> 
>             to
> from        Apple RGB  sRGB CIE RGB   XYZ  Lab  Luv
>    Apple RGB        NA  38.3    55.8  30.3 60.2 56.3
>    sRGB           38.7    NA    55.7  36.5 62.9 52.7
>    CIE RGB        45.2  44.4      NA  30.6 51.5 43.1
>    XYZ            73.4  57.5    69.1    NA 92.2 69.0
>    Lab            46.6  56.6    65.4  72.0   NA 61.3
>    Luv            73.2 107.3    67.3 105.8 97.8   NA
> 
> ## Table 1:
> ## Ratios of `grDevices` to 'level-1' patch speeds for 8000 colors
> ## from each supported color space to all other supported color spaces.
> 
> A few incremental changes as detailed in the level-2 patch [2] yield 
> additional performance improvements:
> 
>             to
> from        Apple RGB  sRGB CIE RGB   XYZ Lab   Luv
>    Apple RGB        NA  97.1   106.2  89.0 117  83.4
>    sRGB           92.5    NA    99.4  86.4 120  76.0
>    CIE RGB       119.2 184.2      NA  82.2 135  83.4
>    XYZ           122.3 209.8   140.9    NA 171 148.8
>    Lab           166.4 168.2   255.4 288.5  NA 265.1
>    Luv           141.7 173.6   279.6 310.1 195    NA
> 
> ## Table 2:
> ## Ratios of `grDevices` to level-2 patch speeds for 8000 colors
> ## from each supported color space to all other supported color spaces.
> 
> Not shown here is that the patched versions of `convertColor` are faster 
> with small inputs as well, though the difference is less marked.
> 
> I have posted tests on github [3], along with the results of running 
> them on my system [4].  While these tests are not proof that the patches 
> do not change the function other than to make it faster, the tests 
> results combined with the narrow scope of the changes hopefully provides 
> sufficient evidence this is the case.   For those wanting to run the 
> tests, installation and testing instructions are on the github landing 
> page for this project [5].
> 
> There are some minor (in my opinion) changes in behavior that need to be 
> discussed:
> 
> * Inputs that would previously stop with errors or work inconsistently 
> now work consistently (e.g. zero-row inputs or inputs containing 
> NA/NaN/Inf).
> * Column names are consistently set to the color space initials; these 
> were previously inconsistently set / mangled by `c`.
> 
> These are discussed at length with examples in [6].
> 
> It would be possible to preserve the existing behavior, but doing so 
> would require some contortions that serve no other purposes than that. 
> Additionally, in many cases the existing behavior is inconsistent across 
> different input/output color spaces.  Finally, most of the differences 
> involve corner case inputs such as those containing NA/NaN/Inf, or zero 
> rows.
> 
> I am entirely amenable to modify the patches to preserve existing 
> behavior in these cases if that is considered desirable.
> 
> These patches should be coordinated with #17473 [7], which I found while 
> working on this issue.
> 
> -----------------------------------------------
> 
> 'level-1' patch:
> [1]: 
> https://raw.githubusercontent.com/brodieG/grDevices2/level-2/extra/level-1.txt 
> 
> 
> 'level-2' patch:
> [2]: 
> https://raw.githubusercontent.com/brodieG/grDevices2/level-2/extra/level-2.txt 
> 
> 
> Tests on github, and the result of running them:
> [3]: 
> https://github.com/brodieG/grDevices2/blob/level-2/tests/convertColor.R
> [4]: 
> https://raw.githubusercontent.com/brodieG/grDevices2/level-2/tests/convertColor.Rout 
> 
> 
> Github landing page for this project:
> [5]: https://github.com/brodieG/grDevices2
> 
> Discussion of differences introduces by patches:
> [6]: 
> https://htmlpreview.github.io/?https://raw.githubusercontent.com/brodieG/grDevices2/level-2/extra/differences.html 
> 
> 
> Indirectly related bugzilla issue #17473:
> [7]: https://bugs.r-project.org/bugzilla/show_bug.cgi?id=17473
> 
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-- 
Dr Paul Murrell
Department of Statistics
The University of Auckland
Private Bag 92019
Auckland
New Zealand
64 9 3737599 x85392
paul using stat.auckland.ac.nz
http://www.stat.auckland.ac.nz/~paul/