[HDR-photo] Re: Measuring *really* small values.

[Blochi]

errr... sorry, apparently that calibration fell off with when saving  
it RLE compressed. Uncompressed it's 7.9 MB, so try www.Blochi.com/ 
files/4cdm_calibrated_in_psphere.exr

Blochi

On Jun 1, 2007, at 12:17 PM, Blochi wrote:

> Maybe this is not the best test image for this. How about putting  
> in some reference patches of 0.5 and 1.0 intensity? A plain 0  
> background might be throwing it off as well...
> Photosphere measures the center patch as 0.0696646 cd/m2, and the  
> surrounding black as 1^-39 cd/m2   ... I calibrated your image in  
> Photosphere for the center patch to be 4 cd/m2, try this file:  
> www.Blochi.com/files/4cdm_calibrated_in_psphere.hdr
>
> Get Photosphere from www.anyhere.com, and also your question is  
> better suited for this list: http://www.radiance-online.org/mailman/ 
> listinfo/hdri
>
> Blochi
>
>
> On Jun 1, 2007, at 11:49 AM, Dan Reetz wrote:
>
>> Hey Ron,
>>
>> In this particular case, noise is not an issue- the HDR image is a CG
>> render from Autodesk Maya, which consists of one bright rectangle and
>> surrounding black space at exactly 0,0,0 for R,G, and B,  
>> respectively.
>> I need super-low values because I am trying to drive our HDR display
>> at very low luminances. On this display, a pixel value of . 
>> 0.000389099
>> will actually result in 24.8cd/m2, and I need to get that down to
>> about 4.
>>
>> But if I were working in camera space, I would definitely take those
>> things into consideration. Thanks!
>>
>> Dan Reetz
>>
>> On 6/1/07, Ronald Murray <kandroma1 at mac.com> wrote:
>>>
>>> When you read this and other values, do you factor in device  
>>> noise levels? There really should be a convention of stating a  
>>> luminance value along with some measure of variation (+/-).
>>>
>>> Selecting larger or smaller patches of the area of interest will  
>>> give you a sense of this, and will let you know how much decimal  
>>> places in the tool readouts matter.
>>>
>>> Ron Murray
>>>
>>>
>>> On Friday, June 01, 2007, at 11:54AM, "Dan Reetz"  
>>> <danreetz at gmail.com> wrote:
>>> >Sorry to reply to my own message.
>>> >
>>> >If I open the file in Photomatix Basic, and open the Histogram,  
>>> is the
>>> >value under Absolute (2.90E-04) the actual pixel value?
>>> >
>>> >Thanks,
>>> >Dan Reetz
>>> >
>>> >On 6/1/07, Dan Reetz <danreetz at gmail.com> wrote:
>>> >> Hi all,
>>> >>
>>> >> I have a Radiance encoded HDR file, and I want to know the  
>>> values of
>>> >> the pixels within. The problem is that they seem to exceed the
>>> >> 3-decimal place accuracy of the tools that I usually use.  
>>> (Meaning, if
>>> >> I use the Info tool in Photoshop or HDRview, they show up as all
>>> >> zeros).
>>> >>
>>> >> Can anyone suggest a tool that can accurately read back the  
>>> values in
>>> >> the center rectangle of this image?
>>> >>
>>> >> http://danreetz.com/for_HDR-photo/4cdm.hdr (170kb)
>>> >>
>>> >> Thanks,
>>> >> Dan Reetz
>>> >>
>>> >_______________________________________________
>>> >HDR-photo mailing list
>>> >HDR-photo at hdr-photography.com
>>> >http://www.hdr-photography.com/mailman/listinfo/hdr-photo
>>> >
>>> >
>>> _______________________________________________
>>> HDR-photo mailing list
>>> HDR-photo at hdr-photography.com
>>> http://www.hdr-photography.com/mailman/listinfo/hdr-photo
>>>
>> _______________________________________________
>> HDR-photo mailing list
>> HDR-photo at hdr-photography.com
>> http://www.hdr-photography.com/mailman/listinfo/hdr-photo
>
> _______________________________________________
> HDR-photo mailing list
> HDR-photo at hdr-photography.com
> http://www.hdr-photography.com/mailman/listinfo/hdr-photo