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I've found some really nice color ramps for portraying rasters, but in ArcGIS and QGIS, they don't seem to be easily usable for a finished product because their complexity causes obvious steps rather than a smooth gradient. The raster renderer appears to be stuck at an 8-bit palette (only 256 levels), rather than a mathematical transform involving 24-bit standard RGB or deep 48-bit RGB.

There's probably an awkward workaround involving splitting up the raster into multiple layers and symbolizing them separately, but I'd like to know which desktop and web GIS systems can present stretched/colorized gradients like this natively in a higher precision format.

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You can spot the GISes that are good for image display with a glance at their output: their maps seem to glow and have a kind of luminous depth. You can expect any GIS that values image processing to do well in this regard. Platforms that I have worked with include

  • Idrisi This may be the fullest featured platform that shines in both the GIS and image processing realms.

  • Manifold So inexpensive that it makes sense to purchase as a supplemental tool even for die-hard ESRI customers.

  • Mathematica This is not really a full-blown GIS (because it does not integrate strong relational data management and a GUI) but it has far more analytical and display capabilities than any GIS, period.

  • R includes many GIS and image processing packages. It has the same deficiencies as Mathematica but a much shorter learning curve and, wonderfully, it's free and open source.

(All links go to pages with sample images.)

Finally, believe it or not, ArcGIS 3 can produce smoother gradients than just 8 bits using an extension I wrote for it long ago. (I apologize for the commercial link: ESRI unilaterally removed the free version of this software I posted on ArcScripts. I will honor personal requests for a free version of the commercial copy.)

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