[Radiance-general] Display of time lapse at constant brightness

[Chris Kallie]

In Wouter's post, he stated "In absolute terms one wall has a luminance 
of 15 cd/m2 at 9:00. That
same wall is 29 cd/m2 at 12:00, yet when displayed (using ximage) it 
appears darker."

I would be interested to understand how the output images would remain 
linear using a tone-mapping algorithm.

The general issue at hand is that some people want visually pleasant 
results, and some need numeric accuracy in the outputs. Perhaps the best 
approach depends upon what the intended use of the output images is, 
imho. (Unless I am not understanding something about the tone-mapping 
algorithm.) -Chris

On 10/3/15 1:03 PM, Greg Ward wrote:
> Andy's recommendation would also be mine, but you need the "-I" option 
> to pcond to get it to read the histogram from stdin.
>
> Cheers,
> -Greg
>
>> *From: *Andy McNeil <mcneil.andrew at gmail.com 
>> <mailto:mcneil.andrew at gmail.com>>
>>
>> *Subject: *Re: [Radiance-general] Display of time lapse at constant 
>> brightness
>>
>> *Date: *October 3, 2015 8:08:16 AM PDT
>>
>> *
>> *
>>
>> You could also use phisto to create a luminance histogram from all 
>> your images and tone map your images using pcond with the all image 
>> histogram as input.
>>
>> phisto frame*.hdr > allframes.hist
>> pcond frame0001.hdr < allframes.hist | ra_tiff - frame0001.tif
>>
>> When there's a wide range of illumination conditions I find that 
>> pcond with the histogram works best to preserve visibility and 
>> maintain consistency between frames.
>>
>> Andy
>>
>> On Sat, Oct 3, 2015 at 5:45 AM, Chris Kallie <kallie at umn.edu 
>> <mailto:kallie at umn.edu>> wrote:
>>
>>     You can use the -e option in pfilt to adjust by a constant.
>>     Instead of using +0, you can use a value without the + symbol
>>     that is a fraction of the EXPOSURE value in your header file. -Chris
>>
>>
>>     On 10/3/15 8:21 AM, ascendilex | Wouter Beck wrote:
>>
>>         Dear Group,
>>
>>         I'm trying to display a series of Radiance renderings as a
>>         time lapse
>>         animation.
>>
>>         I convert (pfilt -e +0 -r .6 -x /2 -y /2 filtered) hdr-images via
>>         ra_tiff and the resulting tifs are combined into an animated
>>         gif via
>>         (ImageMagick's) convert -delay 200 -quality 100 *.tif
>>         time-lapse.gif.
>>
>>         Each image represents a view of an atrium 1 hour apart.
>>         The indirectly lit walls of the room that contains my view
>>         point get
>>         displayed darker as the atrium scene brightens up.
>>         In absolute terms one wall has a luminance of 15 cd/m2 at
>>         9:00. That
>>         same wall is 29 cd/m2 at 12:00, yet when displayed (using
>>         ximage) it
>>         appears darker.
>>         Exposure times in the headers are of course quite different:
>>         vp-A-092108.00.pic:EXPOSURE=3.008155e+00
>>         vp-A-092112.00.pic:EXPOSURE=3.957302e-01
>>
>>
>>         Basically I want the tone mapping according to a constant
>>         (perhaps log)
>>         scale for all images.
>>
>>         How can that be accomplished?
>>         (Looks like falsecolor could do this if it also had a
>>         greyscale palette.)
>>
>>         Best regards,
>>
>>         Wouter
>>
>>
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