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

[Blochi]

OK, it does look like the RLE encoding is the key.
Uncompressed Radiance keeps the values: www.Blochi.com/files/ 
4cdm_calibrated_in_psphere2.zip
Just opening and saving it as RLE encoded Radiance (i.e. in  
Photoshop) brings it back to the 0.696646 that was in your file. So,  
it seems to exceed the precision that the encoding can handle.

Sorry for this monologue.

Blochi

On Jun 1, 2007, at 12:31 PM, Blochi wrote:

> 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
>>>> >>
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>>>> >
>>>> >
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