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This is a weird article. Jet is effectively a divergent colormap and allows highlighting of extemes, but none of the other colormaps they consider are useful in

by blix 6y ago

This is a weird article. Jet is effectively a divergent colormap and allows highlighting of extemes, but none of the other colormaps they consider are useful in this context. Jet isn't competing with batlow and viridis, it's competing with BwR. Yeah batlow looks better than jet on a photograph, but that doesn't mean it's necessarily better for communicating data that doesn't share the underlying features of photographs. I'd like to see whether jet or batlow has better accuracy when asking readers to eyeball data values from -1 to 1 based on color. I personally avoid jet etc, but the motivations they give here seem to miss the point of why these colormaps are used.

deleted 6y ago
[deleted]
rozab 6y ago
I have rarely seen Jet used as a divergent colourmap (i.e. in places where the data is roughly centred around 0), and it would do a particularly poor job at this. There are two perceptual peaks in lightness, in the cyan and yellow sections, and neither of these are centred. Even worse, you can can see in the visualisation of various types of colourblindness that with protanopia only the cyan peak is visible, and with tritanopia only the yellow peak is visible.
- blix 6y ago
  If your data is centered around zero (i.e. lots of uninteresting data points near zero), why would you want your perceptual peak there? I can't think of any divergent colormap that has this feature. In jet the cyan and yellow regions highlight small deviations from zero, which are usually more interesting than zero itself. I understand that jet is poor for accessiblity, and I don't use it for that reason, but in my experience jet is used frequently for divergent data and highlighting extreme values. The article's argument for perceptually uniform colormaps in this context is weak to non-existent. Surely roma wouldn't look very good on a photo of Curie.
  - nemetroid 6y ago
    Why is perceptual uniformity (in each direction) less important for diverging colour maps? Used as a diverging map with zero at green, jet ramps up in intensity up to yellow/cyan, and then ramps down again. As a result it draws attention to mildly deviating areas.
    - blix 6y ago
      It is still important, and jet certainly has major flaws. I just think it's not so useful to compare jet to non-divergent colormaps. Any divergent colormap would look bad on a photograph of a human, which seems to be the main evidence provided in this paper. In a deleted reply to my comment, a user referenced a paper by Borkin [1], that actually compares the quality of decisions made using jet vs other divergent colormaps. Jet loses. It's a shame this sort of argument wasn't included in the ncomms article, because imo it would do a much better job of convincing people who like jet. [1] https://www.eecs.harvard.edu/~kgajos/papers/2011/borkin11-infoviz.pdf https://www.eecs.harvard.edu/~kgajos/papers/2011/borkin11-in...
      - nemetroid 6y ago
        > I just think it's not so useful to compare jet to non-divergent colormaps. I agree, in the "this should be so obvious that it doesn't need an article written about it" sense. But the continued prevalence of jet used as a sequential colour map suggests that the comparison is necessary.
      - rozab 6y ago
        I think the reason the example with the photo is useful is because it shows how the colourmap creates features where none exist in the data (due to the nonlinear gradient). When looking at the photo with Jet I can see discrete areas of flat colour, like the Obama 'Hope' poster, but really these boundaries are just artifacts of the colourmap. I think the same thing happens in the arteries example in that SciPy talk. Sure it could be useful in some scenarios to highlight specific parts of the spectrum (like you mentioned with small deviations from the zero point) but at the end of the day the colourmap doesn't know anything about the data and shouldn't make any assumptions. Highlighting certain small intervals in the data could be better achieved with preprocessing, i.e. some polynomial scaling function.
jamessb 6y ago
> Jet is effectively a divergent colormap I wouldn't describe a rainbow colormap as divergent. A divergent colormap transitions from one color to another, with neutral color in the middle (e.g., from blue to red, passing through white). A rainbow color map transitions between a series of spectrally-orderd distinct colors (red, orange, yellow, green, blue, indigo, violet); this gives rise to apparent discontinuities (e.g. [0]). If you want a divergent color scheme to highlight the extreme values, then use one (see, e.g. [1]) rather than a rainbow scheme. [0]: http://sci.utah.edu/~vdl/papers/2019_eurovis_implicit-discretization.pdf http://sci.utah.edu/~vdl/papers/2019_eurovis_implicit-discre... [1]: https://www.kennethmoreland.com/color-maps/ https://www.kennethmoreland.com/color-maps/
- blix 6y ago
  Not all rainbows are divergent, but if you look at jet you can clearly see it's designed to be roughly symmetric about the mean. Rainbow and divergent are not mutually exclusive.
- wongarsu 6y ago
  Jet transitions from red to blue, with green as a neutral color in the middle. It happens to transition through yellow and cyan to give more possible shades (~more resolution). It's a bad color map for various reasons, but I think it's perfectly fair to call it divergent.
jeffbee 6y ago
The problem with jet is you don't necessarily perceive the ordering. For example would you even notice on a chart colored with jet if all the yellows were missing?
xg15 6y ago
> Jet is effectively a divergent colormap and allows highlighting of extemes I think one of the issues is that it doesn't actually highlight the extremes, but rather some arbitrary values in the middle: The values with the brightest colours as well as the steepest increases in brightness are in the cyan and yellow sections in the middle, whereas the extremes are dark red and dark blue - so attention is actually pulled away from the extremes. Likewise, it highlights some contours but will obscure others - and it's difficult to predict which contours will be highlighted and which will be obscured.

by blix 6y ago

deleted 6y ago

[deleted]

rozab 6y ago

I have rarely seen Jet used as a divergent colourmap (i.e. in places where the data is roughly centred around 0), and it would do a particularly poor job at this. There are two perceptual peaks in lightness, in the cyan and yellow sections, and neither of these are centred. Even worse, you can can see in the visualisation of various types of colourblindness that with protanopia only the cyan peak is visible, and with tritanopia only the yellow peak is visible.

blix 6y ago
If your data is centered around zero (i.e. lots of uninteresting data points near zero), why would you want your perceptual peak there? I can't think of any divergent colormap that has this feature. In jet the cyan and yellow regions highlight small deviations from zero, which are usually more interesting than zero itself. I understand that jet is poor for accessiblity, and I don't use it for that reason, but in my experience jet is used frequently for divergent data and highlighting extreme values. The article's argument for perceptually uniform colormaps in this context is weak to non-existent. Surely roma wouldn't look very good on a photo of Curie.
- nemetroid 6y ago
  Why is perceptual uniformity (in each direction) less important for diverging colour maps? Used as a diverging map with zero at green, jet ramps up in intensity up to yellow/cyan, and then ramps down again. As a result it draws attention to mildly deviating areas.
  - blix 6y ago
    It is still important, and jet certainly has major flaws. I just think it's not so useful to compare jet to non-divergent colormaps. Any divergent colormap would look bad on a photograph of a human, which seems to be the main evidence provided in this paper. In a deleted reply to my comment, a user referenced a paper by Borkin [1], that actually compares the quality of decisions made using jet vs other divergent colormaps. Jet loses. It's a shame this sort of argument wasn't included in the ncomms article, because imo it would do a much better job of convincing people who like jet. [1] https://www.eecs.harvard.edu/~kgajos/papers/2011/borkin11-infoviz.pdf https://www.eecs.harvard.edu/~kgajos/papers/2011/borkin11-in...
    - nemetroid 6y ago
      > I just think it's not so useful to compare jet to non-divergent colormaps. I agree, in the "this should be so obvious that it doesn't need an article written about it" sense. But the continued prevalence of jet used as a sequential colour map suggests that the comparison is necessary.
    - rozab 6y ago
      I think the reason the example with the photo is useful is because it shows how the colourmap creates features where none exist in the data (due to the nonlinear gradient). When looking at the photo with Jet I can see discrete areas of flat colour, like the Obama 'Hope' poster, but really these boundaries are just artifacts of the colourmap. I think the same thing happens in the arteries example in that SciPy talk. Sure it could be useful in some scenarios to highlight specific parts of the spectrum (like you mentioned with small deviations from the zero point) but at the end of the day the colourmap doesn't know anything about the data and shouldn't make any assumptions. Highlighting certain small intervals in the data could be better achieved with preprocessing, i.e. some polynomial scaling function.

jamessb 6y ago

> Jet is effectively a divergent colormap I wouldn't describe a rainbow colormap as divergent. A divergent colormap transitions from one color to another, with neutral color in the middle (e.g., from blue to red, passing through white). A rainbow color map transitions between a series of spectrally-orderd distinct colors (red, orange, yellow, green, blue, indigo, violet); this gives rise to apparent discontinuities (e.g. [0]). If you want a divergent color scheme to highlight the extreme values, then use one (see, e.g. [1]) rather than a rainbow scheme. [0]: http://sci.utah.edu/~vdl/papers/2019_eurovis_implicit-discretization.pdf http://sci.utah.edu/~vdl/papers/2019_eurovis_implicit-discre... [1]: https://www.kennethmoreland.com/color-maps/ https://www.kennethmoreland.com/color-maps/

blix 6y ago
Not all rainbows are divergent, but if you look at jet you can clearly see it's designed to be roughly symmetric about the mean. Rainbow and divergent are not mutually exclusive.
wongarsu 6y ago
Jet transitions from red to blue, with green as a neutral color in the middle. It happens to transition through yellow and cyan to give more possible shades (~more resolution). It's a bad color map for various reasons, but I think it's perfectly fair to call it divergent.

jeffbee 6y ago

The problem with jet is you don't necessarily perceive the ordering. For example would you even notice on a chart colored with jet if all the yellows were missing?

xg15 6y ago

> Jet is effectively a divergent colormap and allows highlighting of extemes I think one of the issues is that it doesn't actually highlight the extremes, but rather some arbitrary values in the middle: The values with the brightest colours as well as the steepest increases in brightness are in the cyan and yellow sections in the middle, whereas the extremes are dark red and dark blue - so attention is actually pulled away from the extremes. Likewise, it highlights some contours but will obscure others - and it's difficult to predict which contours will be highlighted and which will be obscured.