How to get extreme values from a falsecolor image

Hello everyone,

Falsecolor's documentation states that "The *-e* option causes extrema
points to be printed on the brightest and darkest pixels of the input
picture."

Is there any way to output (not print on image) the extrema values? This
could be helpful in appropriately scaling the "scale".

Thank you!

Best regards,
Vaib

1 Like

Hi Vaib,

A couple of things:

Thing One: there is an –a option, which “autoscales” the max value for the scale to peak at the max value found in the image.
Thing Two: yes, you can use pextrem to get the min and max values (in Rr,Rg,Rb) printed to the command line.

- Rob

···

From: Vaib [mailto:vaibhavjain.co@gmail.com]
Sent: Wednesday, February 05, 2014 9:39 AM
To: Radiance general discussion
Subject: [Radiance-general] How to get extreme values from a falsecolor image

Hello everyone,

Falsecolor's documentation states that "The −e option causes extrema points to be printed on the brightest and darkest pixels of the input picture."

Is there any way to output (not print on image) the extrema values? This could be helpful in appropriately scaling the "scale".

Thank you!

Best regards,
Vaib

Hello everyone,

I have the same problem as Vaib. I would like to output the extrema values that I obtain with the -e option in falsecolor.

I have tried pextrem, but the values printed are not the same that I have in the falsecolor image and I don’t know how to convert those values to the one in the falsecolor image.

Is there any way to output the falsecolor extrema value to be used in a table?

Thank you in advance!

Irene

Hello Irene,

falsecolor -e processes the raw r,g,b value with a scale (given by -m, the default is 179 for cd/m^2) and a photopic brightness. To print the equivalent value using pextrem (changing 179 if you are using a different unit):

pextrem image.hdr | rcalc -e 'grey(r,g,b):r*.27+g*.67+b*.06;$1=grey($3,$4,$5)*179'

if you are only interested in the maximum, add a condition:

pextrem image.hdr | rcalc -e 'grey(r,g,b):r*.27+g*.67+b*.06;$1=grey($3,$4,$5)*179;cond=recno-1'

Thank you so much for your answer.

That’s very valuable for me.

Irene