backward recreatoin of an lut

Posted by rustyconc on Jun 05, 2015; 4:33am
URL: http://imagej.273.s1.nabble.com/backward-recreatoin-of-an-lut-tp5013041.html

Hi,

I am trying to do a quick analysis of satellite data available from NASA here:
http://oceancolor.gsfc.nasa.gov/cgi/l3

For example, this thumbnail (for quick download):
http://oceancolor.gsfc.nasa.gov/cgi/l3/V20142742014304.L3m_MO_NPP_CHL_chlor_a_4km.nc.ico.png?sub=img&novl=1

The problem is the available image format is PNG, which imports into imagej as an RGB.  However, the images are false-colored, according to a LUT provided in another PNG image:
http://oceancolor.gsfc.nasa.gov/images/NPP_CHL_chlor_a_colorscale.png

Is there an easy way to convert the data RGB image to 8 bit gray scale so that the colour scaling in the color scale image is preserved?

Disclaimer re alternatives:  I know there are other portals to access this data, and I'm going about it backwards: delving into NASA's system would allow direct download of the data.  However, the complexity sky-rockets (likely involving Matlab to handle hdf files) and the monthly PNG images are exactly what I need to work with, and this portal provides the highest resolution available.

Thanks
Russell