Color Tables in the Era of Super-Resolution

(Updated 15 Dec 2008 for Spectrum Width)

During OB9 PIT testing back in June one of the comments about radar displays concerned color tables. Specifcally, the AWIPS GSD default reflectivity and velocity color tables used for testing at PIT were not useful. Additionally, it is fairly well agreed upon from field personnel that the OSF reflectivity color tables also may not be the best choice for super-res reflectivity because of the increased noise in the data. Thus, this page will allow you to compare reflectivity and velocity images using WDTB default, AWIPS default, and OSF color tables. We are not recommending removing any color tables, just adding one each for Z and V, and making them the defaults.

After field queries and research, it is felt that a majority of field sites use color scales similar to WDTB's for 8-bit and super-res Z and V. In fact many offices have asked us to send them those color tables to use operationally. This change would be low-risk since most users create and use their own color tables in their procedures.

8-bit STP color table are also provided for review at the very bottom, only because if change is made to Z and V, why not take the opportunity to improve another widely used product's default color table.

***Super-res Spectrum width color tables are now available at the bottom.***

NOTE: Opinions on this page are of WDTB only, and we realize color table preference is inherently subjective.

This is the proposed default reflectivity color table, made at WDTB based off an extremely popular color table that was first created for 8-bit data by Evan Bookbinder (now with EAX). Bookbinder's color table needed to be modified in the super-res era because there were no smooth transitions in the 20-40 dBZ range. Notice in this graphic that the stratiform region in the NE quandrant looks less noisy to the eye than the OSF and AWIPS default tables. Bookbinder liked this particular color table better than his original, and now uses it operationally. Most offices have a color table very similar to this one since this was based on Bookbinder's original. It is also very good for viewing the low-level reflectivity values. A different reflecitivity graphic is available further down the page to examine a low-level boundary.

Here is the AWIPS default. Transitions at moderate reflectivities are too stark, making the product look more noisy to the eye. Also, blue-orange between 20-40 dBZ is distracting.

This is a popular color table that many offices use or used to build a custom table because of it works well especially above 10 dBZ. There are two problems with the scale in the super-res era: 1. Transition at moderate reflectivity makes product look noisy to the eye. At low reflectivities, the teal is so bright it seems distracting. This disadvantage will be shown more clearly with another example further down the page.

Here is another example of the proposed default color table for reflectivity (WDTB's Default), this time showing a sharp low level boundary and lots of clear air returns. The lowest reflectivities associated with the cold front and clear-air returns show up well, but are not distracting. Far NE part of the display notice that this does not stand out as being particularly noisy to the eye. Note that this example is not super-res, just 8-bit 1degree azimuth.

Current AWIPS default. Low-level returns show up well and are not too distracting, but rest of data look too noisy and distracting.

OSF default. This color table in this example looks pretty good, especially above the low values. The 20-30 dBZ transition is really sharp but in this graphic that doesn't adversely affect the display that much, mostly because this is not super-res. Notice how much the clear air returns stand out in this example, with the bright greens and blues. This can be distracting in these situations, and we feel the WDTB scale makes up for that deficiency.

WDTB default 8-bit velocity. This has not changed much if at all from Bookbinder's widely popular 8-bit velocity color table created when 8-bit products hit the field. Transitions are much smoother than the other two color tables, and relative to the OSF color table higher velocity values are much more easily seen.

AWIPS default. Is very poor at utilizing all 256 color levels. Sharp transitions all over.

OSF Default 8-bit Velocity. Also does not utilize 256 data levels. Not enough color contrast between 50-60 kts and 20 kts.

This is the WDTB default color table for 8-bit storm total precipitation, created by Bookbinder. This color table is much easier to interpret and utilizes the 256 data levels well, with sharp contrasts at the important whole inch values.

Here is the default color table, which follows the same scheme as the default 8-bit reflectivity. Not as easy on the eyes.

Here is the OSF color table. Looks as good as the WDTB default other than we feel that the lower end of the scale is too bright.

Here is the WDTB Default for 8bit, Super-res spectrum width, 95% of which was built by Evan Bookbinder (EAX). I also received a color table from the SOO in PAH (Pat Spoden) who has been using Super-res SW for squall line analysis. His color table had identical break points (~19 kts and ~9.7 kts) to Evan's/ours, and also went black to grey on the low end. The only difference between the two were the colors chosen for values about ~9.7 kts. In this proposed color scale we have added a light blue for exactly 0.0 Spectrum Width.

Here is the 8bit version applied to a 3bit product.

Here is the Super-res SW AWIPS default. Thte 4-8 kts stick out too much and make analysis difficult across the display. 12-16 kts too dim.

Here is the Super-res SW OSF default. This one is similar to the WDTB proposed, but does has sharp transitions. for SW this may or may not be desireable. In the limited conversations with field experts, they like more gradual transitions other than at the noise level (~19kts) and half the noise level (~9.7), which is where the proposed WDTB scale is sharp.

Here is the same OSF color scale applied to 3bit. Here the transitions are not a big deal of course, but it's pretty important to have the same color scale applied to SR and 3bit to help in analysis.