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Great points, but in the author's 2D histograms the use of 'color' to show point density is a little misleading. Color is not a scalar, it's a vector, and simpl

Great points, but in the author's 2D histograms the use of 'color' to show point density is a little misleading. Color is not a scalar, it's a vector, and simply varying hue doesn't map out well to the human perception of lightness or intensity. It also doesn't allow for meaningful interpolation. If you take a look at http://vis4.net/blog/posts/avoid-equidistant-hsv-colors/ http://vis4.net/blog/posts/avoid-equidistant-hsv-colors/ you can see a strategy for building perception-aware color palettes/gradients, which would be much more useful in this case. (actually it looks like this wasn't the author's decision, but something built into the graphing library)

pacmon 14y ago
Interesting article you linked to and something to consider certainly. That being said, I somewhat disagree with you about the histograms being misleading. His color scheme looks to be based much the same as thermal imaging. Which I find is quite clear about what are the 'hot' zones (or in this case high point density) and the 'cold' zones (or low point density).
- harpastum 14y ago
  I think zacharyvoase's point was that it might either emphasize or deemphasize how much hotter or colder something was. Because the eye doesn't see blue->yellow->red hue changes consistently, what looks like a "big" change on the graph might actually be fairly small.
kulkarnic 14y ago
I agree with you. I think it's better to use transparency to show density-- here's an example from ggplot2: http://had.co.nz/ggplot2/graphics/25464f1f2c009d435b862debcad8db51.png http://had.co.nz/ggplot2/graphics/25464f1f2c009d435b862debca... and the page in general at http://had.co.nz/ggplot2/geom_point.html http://had.co.nz/ggplot2/geom_point.html And if you do this overplotting with partly transparent data points, you can even continue using scatterplots (which have several benefits over binned color density plots, such as showing the actual data, rather than summaries).
wahnfrieden 14y ago
Agreed - good article, but terrible heat maps. Another great article about this: http://www.research.ibm.com/people/l/lloydt/color/color.HTM http://www.research.ibm.com/people/l/lloydt/color/color.HTM

pacmon 14y ago

Interesting article you linked to and something to consider certainly. That being said, I somewhat disagree with you about the histograms being misleading. His color scheme looks to be based much the same as thermal imaging. Which I find is quite clear about what are the 'hot' zones (or in this case high point density) and the 'cold' zones (or low point density).

harpastum 14y ago
I think zacharyvoase's point was that it might either emphasize or deemphasize how much hotter or colder something was. Because the eye doesn't see blue->yellow->red hue changes consistently, what looks like a "big" change on the graph might actually be fairly small.

kulkarnic 14y ago

I agree with you. I think it's better to use transparency to show density-- here's an example from ggplot2: http://had.co.nz/ggplot2/graphics/25464f1f2c009d435b862debcad8db51.png http://had.co.nz/ggplot2/graphics/25464f1f2c009d435b862debca... and the page in general at http://had.co.nz/ggplot2/geom_point.html http://had.co.nz/ggplot2/geom_point.html And if you do this overplotting with partly transparent data points, you can even continue using scatterplots (which have several benefits over binned color density plots, such as showing the actual data, rather than summaries).

wahnfrieden 14y ago

Agreed - good article, but terrible heat maps. Another great article about this: http://www.research.ibm.com/people/l/lloydt/color/color.HTM http://www.research.ibm.com/people/l/lloydt/color/color.HTM