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

[Dan Reetz]

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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