Re: Exposure Value
Re: Exposure Value
- Subject: Re: Exposure Value
- From: Robin Myers via colorsync-users <email@hidden>
- Date: Sat, 22 Jun 2019 10:31:28 -0700
Hello Mr. Breton,
When you are looking for a new gray card, may I suggest that the SNI value
calculated in SpectraShop may be of use. The SNI is the Spectral Neutrality
Index, a value which I have developed to evaluate neutral references. This
value is an indicator of a specimen's spectral uniformity. The scale is 0-100,
with 100 being a spectrum that is monotonic in value. Here are some example SNI
values.
Perfect reflecting diffuser 100
Fluorilon FWS-99 2009 99.9
Spectralon SCS-99 99.7
Kodak Gray Card 1977 (3 specimen average) 95.0
ColorChecker Passport 2013-12 Neutral 9.5 52.2
ColorChecker Passport 2013-12 Neutral 5.0 95.2
The SNI formula is based solely on the spectral values, no perception is
involved. This allows for material evaluation alone.
Notice that the white patch (Neutral 9.5) of the CC Passport has a much lower
SNI than the Neutral 5 patch from the same chart. This is due to the high
absorbance of violet wavelengths by the titanium dioxide colorant used for the
white and also the slightly yellow color of the same titanium dioxide. This can
be readily observed by placing a Fluorilon or Spectralon 99% reflecting tile
(scintered PTFE) next to any white material containing titanium dioxide (TiO2).
The TiO2 material will appear slightly yellow since the human vision system
will adapt to the tile’s white, allowing the true color of the TiO2 to be
observed.
The SNI value was created specifically to answer questions about which material
is more spectrally neutral. I find it very useful for checking gray reference
materials such as gray cards.
These articles on my website may also be of use.
Neutral References for Digital Camera Calibration
http://chromaxion.com/information/neutral_references.html
<http://chromaxion.com/information/neutral_references.html>
Gray or White Card for Neutral Balancing?
http://chromaxion.com/information/gray_or_white.html
<http://chromaxion.com/information/gray_or_white.html>
Regards,
Robin Myers
Robin Myers Imaging
email@hidden
email@hidden
925-519-4122
> On 21 Jun 2019, at 19:14, Roger Breton via colorsync-users
> <email@hidden> wrote:
>
> Dear Ilah,
>
> Thank you so much for applying your vast technical expertise to my humble
> problem. I realize, again, that there is so much to learn in digital
> photography, I feel ashamed to have neglected digging into this fascinating
> part of image processing for so long (It took me more than a few CPU cycles
> of my brain to figure Exposure Value, today)...
>
> For sure, I need to invest in a "new" gray card, I confess that this one has
> seen its share of "tales from the trenches".
>
> Having said that, I'm relieved to read in your analysis that my camera "light
> meter" isn't playing tricks on me or need to go back to the manufacturer
> under warranty.
>
> I *will* reshoot, for sure, as you suggested. It's an exercise worth every
> effort and probably investigate using one of your suggested software..
>
> For now, I am not sure what to conclude from my experience? Tomorrow, I will
> probably experiment with shooting A) RAW alone and shooting B) RAW + JPEG. In
> "theory", there should not be any difference between the two modes of
> shooting but if there should be one, then this is going to prove interesting.
>
> Have you had a chance to take a look at my Excel sheet at all? To see whether
> I correctly applied the metering equations from measured Luminance and
> Illuminance?
>
> I think the calculations are sound.
>
> One last thing I have not tried and I *will* try is, to shoot with my antique
> D100, in RAW, to compare with shooting the same scene with the D810, in RAW,
> to test any potential differences between the two systems, in terms of
> exposure.
>
> One thing I wonder, as I was thinking about the experimental setup, something
> completely absurd (?), was, what that, could there be any difference in the
> underlying capture of the pixels between the two cameras?
>
> Suppose, on the D810, at 1/200s, F/5.6, ISO400, the histogram looks skewed to
> the left, suggesting some degree of under-exposure (see my earlier links)?
> Suppose further, on the D100, at the same 1/200s, F/5.6, ISO400 settings, the
> histogram looks "normal", with pixels distributed throughout the tonal range,
> from 0 to 255, then what?
>
> Until I'm convinced that there is nothing wrong with this camera, I figure I
> need to further test it, until I'm fully satisfied that there is nothing
> "wrong" with it.
>
> Best regards / Roger
>
> -----Original Message——
<snipped for brevity>
_______________________________________________
Do not post admin requests to the list. They will be ignored.
colorsync-users mailing list (email@hidden)
Help/Unsubscribe/Update your Subscription:
This email sent to email@hidden