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
p...@stat.auckland.ac.nz
http://www.stat.auckland.ac.nz/~paul/
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