[Radiance-general] Obtaining proper luminance values in scene image generated using HDR sky-probe luminance data

[Mehlika Inanici]

Kyle,

You can set the exposure to 1 (pfilt)  to prevent the problems you are experiencing with the probe.


Mehlika

On Fri, 23 Nov 2012, Kyle Konis wrote:

> Dear list,
>
> I am exploring image-based lighting in Radiance and have encountered
> several issues with the luminance values in the scene images i am
> generating. I am starting with a hemispherical fisheye image of the
> sky which must be cropped to a square format via pcompos.
>
> This process leads to a header which puts the EXPOSURE=5.953331e-03 in
> a location which creates a problem in that the pixel values, as viewed
> in Photosphere or when rendered via rpict to a test image (looking up
> from the origin at the sky), are much lower than the original HDR
> image.
>
> #?RADIANCE
> CAPDATE= 2012:10:21 17:05:24
> GMT= 2012:10:22 00:05:24
> 20111019_cloudy/201110191248.hdr:
>        CAMERA= Canon Canon PowerShot A570 IS version v.0
>        EXPOSURE=5.953331e-03
>        VIEW= -vtv -vh 52.456387 -vv 40.558973
>        CAPDATE= 2011:10:19 12:48:08
>        hdrgen created HDR image from 'IMG_0685.JPG' 'IMG_0684.JPG'
> 'IMG_0683.JPG' 'IMG_0682.JPG' 'IMG_0681.JPG'
>        PRIMARIES= 0.6400 0.3300 0.3000 0.6000 0.1500 0.0600 0.3127 0.3290
> pcompos -x 1280 -y 1280 20111019_cloudy/201110191248.hdr -340 -100
> pfilt -1 -x 600 -y 600
> pflip -v -c
> pflip -h -c
> FORMAT=32-bit_rle_rgbe
> protate -r -c
>
> -Y 600 +X 600
>
>
> In other words, when the EXPOSURE=5.953331e-03 line is in its
> original position, e.g.:
>
>
> #?RADIANCE
> CAMERA= Canon Canon PowerShot A570 IS version v.0
> EXPOSURE=5.953331e-03
> VIEW= -vtv -vh 52.456387 -vv 40.558973
> CAPDATE= 2011:10:19 12:48:08
> hdrgen created HDR image from 'IMG_0685.JPG' 'IMG_0684.JPG'
> 'IMG_0683.JPG' 'IMG_0682.JPG' 'IMG_0681.JPG'
> PRIMARIES= 0.6400 0.3300 0.3000 0.6000 0.1500 0.0600 0.3127 0.3290
> FORMAT=32-bit_rle_rgbe
>
> -Y 1536 +X 2048
>
> ...... all is well, and the image displays the correct luminance
> values for the sky in Photosphere.  Because i need to crop this image
> to a square format to use it as a light probe, i cannot confirm that a
> test image (again, looking up from the origin) would render with the
> proper luminance values, but my guess is that it would.
>
>
> I am using the following text to describe an image-based lighting
> environment consisting of a hemispherical fish-eye image of the sky.
>
> # Image-Based Lighting Environment
> void colorpict hdr_probe_image
> 7 red green blue sky_image/HDR_sky_temp.hdr angmap_sky.cal u v
> 0
> 0
>
> # specify a "glow" material that will use this image
> hdr_probe_image glow light_probe
> 0
> 0
> 4 1 1 1 0
>
> light_probe source ibl_environment
> 0
> 0
> 4 0 0 1 180
>
>
>
> I have tried a number of scripts to manipulate the header text to
> return the EXPOSURE=5.953331e-03 line to a location where it is again
> utilized.  In this example (below), which just sticks the line up at
> the top, Photosphere reads the image and scales the pixels by the
> exposure value. However, when a scene is rendered using the image as a
> light probe, the test image again has very low sky luminance values.
>
>
> #?RADIANCE
> EXPOSURE=5.953331e-03
> #?RADIANCE
> CAPDATE= 2012:10:21 17:05:24
> GMT= 2012:10:22 00:05:24
> 20111019_cloudy/201110191248.hdr:
>        CAMERA= Canon Canon PowerShot A570 IS version v.0
>        EXPOSURE=5.953331e-03
>        VIEW= -vtv -vh 52.456387 -vv 40.558973
>        CAPDATE= 2011:10:19 12:48:08
>        hdrgen created HDR image from 'IMG_0685.JPG' 'IMG_0684.JPG'
> 'IMG_0683.JPG' 'IMG_0682.JPG' 'IMG_0681.JPG'
>        PRIMARIES= 0.6400 0.3300 0.3000 0.6000 0.1500 0.0600 0.3127 0.3290
> pcompos -x 1280 -y 1280 20111019_cloudy/201110191248.hdr -340 -100
> pfilt -1 -x 600 -y 600
> pflip -v -c
> pflip -h -c
> FORMAT=32-bit_rle_rgbe
> protate -r -c
>
> -Y 600 +X 600
>
>
> My questions to the list, ultimately are:
>
> 1) Does the colorpict pattern type, or image-based lighting process in
> general, have any relationship to the EXPOSURE value of the HDR image?
> If not, i suppose the solution is to scale all the pixel values in
> the image and forget about where the EXPOSURE line is in the header.
>
> 2) If the EXPOSURE line in the header is relevant, can anyone
> recommend a scripting technique to cook up the proper header text and
> then attach the binary image data from the manipulated (e.g. pcompos,
> pflip, pfilt) HDR images? For example, i have used "getinfo" to grab
> the header from the original image and "grep" to grab the EXPOSURE
> line, i write these to a new file (with #?RADIANCE) as the first line.
> I then cat the manipulated image file to this new file. This results
> in an inelegant header for the new file, works in Photosphere, but, as
> mentioned above, does not lead to a proper sky luminance results when
> used to generate scene images in radiance.
>
> Any suggestions would be appreciated!
>
>
> -Kyle
>
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