Revise monochromatic color tables
|Reported by:||wenzeslaus||Owned by:|
|Keywords:||r.colors, d.rast, blues, greens, oranges, reds, sepia, water||Cc:|
The monochromatic color tables namely
reds added in r64283 start with white. It is probably obvious that it is good that there is no black but I think that they also should not contain white.
Using r.mapcalc, r.colors, and r.colors.matplotlib (
g.extension r.colors.matplotlib), you can try how the Matplotlib
Reds look like.
color=blues map=m_$color g.region cols=500 rows=300 n=-300 s=-600 w=0 e=500 r.mapcalc "$map = col() / 10 + 2 * cos(col() * 100)" r.colors map=$map color=$color
color=Blues map=m2_$color g.region cols=500 rows=300 n=-600 s=-900 w=0 e=500 r.mapcalc "$map = col() / 10 + 2 * cos(col() * 100)" r.colors.matplotlib map=$map color=$color
Also Moritz mentioned off-list that a quick look at Color Brewer shows that they use values such as:
255:255:229 for greens 255:247:236 for reds
You can notice that besides different start color Matplotlib uses also different end color. Our color versions end e.g. with 0:0:255 (called
blue in GRASS) which is an arbitrary color based on its special position in the RGB model not on its optical or aesthetic features. For the technical part, the
blues does not show the waves on the right and in comparison with the Matplotlib versions it seems to me that even
oranges show less waves on the right.
I'm not sure how many color steps are needed for the Matplotlib colors. I used 6 but perhaps just 2 (start and end) are enough.
sepia color table from r33163 actually starts with white,
0:0:0, and ends with (almost) black,
255:254:251, (or the other way around when you don't use
-n), so that's not good I think. I'm usually not able to use it because of the black color. The gray scale image and the waves are good (these two look like good indicators, see #3043). So, I would just remove the stretch the current colors unless there is some good sepia color table source.
sepia color table from r68464 (from r.lake) doesn't show a big gradient in gray scale (which might be good thing sometimes, but not now). However, there is some and I don't know how to change it while preserving other features especially the look which I think is really good here.
Note that changing these would be more serious change in behavior because your result is changed even if you explicitly specify what you want (which is not the case for change of default in #3043 where you just trust the default which is changed for your good).
Note also that a monochromatic color tables are candidacies for new default color table (#3043).