[Radiance-general] 3.8 Falsecolor Scale

[Gregory J. Ward]

I never put in an option to set the falsecolor scale to the image  
maximum because it's usually the wrong thing to do.  There are often  
a few really bright pixels in a scene that may be orders of magnitude  
above the rest.  It's better to go in manually with ximage and use  
the 'l' key to pick out luminance values in the bright regions and  
set the scale based on those.

-G

> From: Rob Guglielmetti <rpg at rumblestrip.org>
> Date: November 11, 2006 9:21:50 PM PST
>
> On Nov 11, 2006, at 11:14 AM, Mark de la Fuente wrote:
>
>> I find people understand the blue - red scale as well.  Since  
>> falsecolor images are usually presented to clients, having  
>> "bloody" pictures is often a very effective communication tool.   
>> Probably some psychological thing that dates back to hunting  
>> mammoths saber tooth tigers!
>
> I agree with the red=danger aspect; it's one of the things I like  
> about the scale.  Blue is calming, red is alarming.  And another  
> thing: clients freak out enough with the few colors we show them  
> sometimes; adding more color to the mix may make things worse.   
> John, I can see where you are coming from (Greg too), and I think  
> both scales have merits.  THanks Greg for adding the "-spec" option.
>
>>
>> I suppose in Radiance one could to a pextrem command on a picture  
>> to get the maximum value and then use that to set the scale, but  
>> having it spit out something like the following can be a little  
>> intimidating.  :)
>>
>> 499 499 0.000000e+00 0.000000e+00 0.000000e+00
>> 322 218 2.706250e+01 2.693750e+01 2.706250e+01
>>
>> I've tried to use this before, but have come up with numbers I  
>> don't feel comfortable using.
>
> Hmmm, what do you mean, you don't feel comfortable with these  
> numbers?  I use pextrem all the time in conjunction with  
> falsecolor.  If you simply run 'pextrem -o' on a radiance image and  
> multiply the green channel of the high pixel by 179, you have your  
> maximum value for the -s option.
>>
>> Seems like a "-s max" setting would be useful.  Where setting the  
>> scale to "max" would automatically check the image and set the  
>> scale to the max pixel value automatically.
>
> yeah, and this is probably easy for anyone who doesn't suck at  
> programming, as I do.  I just spent longer than I care to share  
> trying to add such an option to falsecolor.  It should be easy, but  
> I couldn't sort out what values to use for certain variables.  Greg  
> has already done a lot of the work, since the -e option already has  
> code to run pextrem to find the max (and min) values and assign  
> them to variables within the script (falsecolor is actually just a  
> shell script).  But I don't know how the scale option gets applied  
> to the legend.  (Greg, I can share with you what I have so far, if  
> you wanna take it the rest of the way. )
>
> - Rob