I Don't Understand the Luminous Landscape "Expose Right" Article

I Don't Understand Luminous Landscape "Expose Right" Article

Anyone wishing to understand the article could run this simple test ...
pick a fairly monotone subject (sky, gray card, etc) and shoot it in
RAW mode at ISO 400 metered properly, then set your exposure
compensation +2 and shoot it again, then -2 and shoot it again. When
you convert the three RAW files don't make any exposure adjustments to
the first image, adjust the +2 image by -2 stops, adjust the -2 image
by +2 stops. You should have roughly equivalent exposures by now if
you convert these ... check the noise levels of the three "equivalent"
exposures" and you'll see what he means.

You could have gotten the same improvement that the +2 image gives by
shooting as metered at ISO 100.

Try it and see.

The article is discussing the behavior of digital cameras not film. How
many levels you have in film is not so clear cut, you can deal with the
SN of film and get some sense of it, Roger Clark has done a lot of work
on this, see this link

http://clarkvision.com/imagedetail/d...ignal.to.noise

Scott

In message .com,
"Bill Hilton" wrote:

I Don't Understand Luminous Landscape "Expose Right" Article

Anyone wishing to understand the article could run this simple test ...
pick a fairly monotone subject (sky, gray card, etc) and shoot it in
RAW mode at ISO 400 metered properly, then set your exposure
compensation +2 and shoot it again, then -2 and shoot it again. When
you convert the three RAW files don't make any exposure adjustments to
the first image, adjust the +2 image by -2 stops, adjust the -2 image
by +2 stops. You should have roughly equivalent exposures by now if
you convert these ... check the noise levels of the three "equivalent"
exposures" and you'll see what he means.

This should be true, but some RAW converters treat RAW data based upon
their absolute values, and not the values after a purely linear
"exposure" adjustment. ACR, for example, nails the highest RAW values
to 255 in the output, no matter if you use -4 "exposure".

You could have gotten the same improvement that the +2 image gives by
shooting as metered at ISO 100.

Not exactly; ISO 400 at +2 EC is usually better quality than ISO 100 at
0 EC, if the RAW data doesn't clip.

Try it and see.

--


John P Sheehy

Scott W wrote:

The article is discussing the behavior of digital cameras not film. How
many levels you have in film is not so clear cut, you can deal with the
SN of film and get some sense of it, Roger Clark has done a lot of work
on this, see this link

http://clarkvision.com/imagedetail/d...ignal.to.noise


And figure 5 on this page:
http://clarkvision.com/imagedetail/dynamicrange2
which does discuss film/digital

I still find that one shocking, particularly given the implication that
digital has less info in the shadows than digital highlights. But still
digital has more information in the shadows than film.

But that is not really what the luminous landscape article is discussing
I think. They are talking about how RAW digital files carry more info in
the highlights due to their being linear data of simple intensity.
That's the best I can understand anyways. Brighter means bigger number
in that linear scheme so there are more significant digits to assign
finer gradations of tonal range. Once it's converted from RAW, that
extra info is dropped. During the RAW conversion process, there is an
opportunity to sneak up & expand that highlight information before
dropping it.


One result of this effect (if I understand correctly -and I'm unsure) is
that an unmanipulated RAW image looks too dark & muddy. Most of the
information is crammed in the highlights. A curve needs to be applied to
the image to increase contrast back to what our non-linear eyes expect
to see.

Maybe someone can comment on whether the diagrams below correctly
explain the situation. Normal scenes appear to our eyes with most of the
complexity in the middle ranges and not a lot going on in the highlights
or shadows. Digital RAW format contains extra highlight data which is
generally useless unless you stretch it to the left before clipping to a
normally curved format. So yes RAW has less info in the shadows but it
has all it needs as long as you don't need to adjust the contrast later.
I think film is in the same boat on the shadow end of the chart, in fact
according to the figure 5 mentioned above, film has less shadow detail
and less room for adjusting highlight detail.

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shadow highlight

1. LINEAR RAW DATA

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shadow highlight

2. NORMAL (FILM, EYE, TIF, JPEG) -Bell Curve


Or I could be misunderstanding. I'm just trying to learn as I go.

paul wrote:

One result of this effect (if I understand correctly -and I'm unsure)
is
that an unmanipulated RAW image looks too dark & muddy. Most of the
information is crammed in the highlights. A curve needs to be applied
to
the image to increase contrast back to what our non-linear eyes
expect
to see.

The raw file holds the light values for the pixel in a linear format,
the normal jpg format is going to hold the data in a non-linear format
to fit more dynamic range in the 8 bits. This is done with the gamma of
the image, the light level is proportional to the pixel level raised to
the gamma power. A common gamma that is used is 2.2, this is what
photos that are in the sRGB color space use. This also turns out to be
the gamma of most PC monitors, MACs use a lower number of 1.8.

So it has nothing to do with our non-linear eye and everything to do
with our non-linear monitors.

Scott

John Sheehy writes ...

ACR, for example, nails the highest RAW values
to 255 in the output, no matter if you use -4 "exposure"

We must be talking about something totally different, because this is
total nonsense ... in the test shots I mentioned (monotone subject --
in my case a heavily overcast sky -- at 0, +2 and -2) a straight
conversion using ACR of each image leaves me with these RGB values for
the brightest part of the sky ... 60/67/79 for the -2 shot, 129/140/165
for 0, 223/229/246 for the +2. Think about it ... if what you say is
correct (it isn't) then every monotone image would get mapped to white,
which obviously doesn't happen.

You could have gotten the same improvement that the +2 image gives
by shooting as metered at ISO 100.

Not exactly; ISO 400 at +2 EC is usually better quality than ISO 100
at
0 EC

Run the test and compare the noise levels. That's what I did. ISO 100
looks the same as ISO 400 at +2 corrected for exposure with Capture One
....

Bill

jim evans writes:

Last fall I emailed Thomas Knoll this question. After he did not
reply, early this year I emailed the question to Michael Reichmann.
He did not reply either. I have posted a copy of the question I sent
Reichmann at http://factsfacts.com/LuminousLandscape.htm.

The table in the article shows the tonal values of an image shot with
a digital camera as a geometric distribution, and implies that the
tonal values of film are distributed linearly. Are the tonal values
of film really distributed linearly in this context?

First, the digital camera response isn't a "geometric distribution".
The response is linear. But the terms in the left-hand column of your
chart are logarithmic. The top row is labelled "within the first
f/stop", which by definition contains all tones between 1/2 of maximum
and maximum. Naturally, because the sensor and A/D converter are
linear, half of the available codes are assigned to this half of the
brightness range.

The problem with this approach is that the *eye* isn't linear. It sees
the step from full brightness to 1/2 brightness as being about the same
size as the step from 1/2 to 1/4, which is the same as from 1/4 to
1/8. So if you have a limited number of bits available (e.g. 24 bit
colour, with only 256 codes per colour), you're better off to use a
nonlinear transformation to spread the available codes so that each stop
of range gets something like the same number of codes. This is in fact
done.

Second, what do you mean by "the tonal values of film are distributed
linearly"? Film itself is analog; it has no levels or steps. Digitized
film *does* have levels, but the distribution of them depends on the
software running the film scanner. Some film scanners output data that
is proportional to film density, which is the logarithm of
transmittance. In this case, there will be about the same number of
code values per each one-stop range of input brightness. Some scanners
output linear data - but it's linear in film transmittance, not original
scene brightness. And there are other possibilities.

Basically, your question makes no sense unless the right column is about
*some specific film, scanner, and software* combination. Film itself
has no levels.

If you reply please do so as requested in my question to Reichmann.
That is, please either agree that my "Film" column in the table is
correct, or give the 5 values that should be in the Film column.

Your question is unanswerable as posed. There is no answer that would
apply to all film scanners.

Dave

On Fri, 25 Feb 2005 10:16:37 -0600, jim evans
wrote:

I Don't Understand Luminous Landscape "Expose Right" Article
----snip----
If you reply please do so as requested in my question to Reichmann.
That is, please either agree that my "Film" column in the table is
correct, or give the 5 values that should be in the Film column.

Jim:

I don't understand why you are trying to make a comparison to film.
That article is strictly about digital photography, one of the quirks
of using an electronic sensor, and how to compensate for it.

It has nothing to do with using film, it implies nothing about the
behavior of film. There is no connection to using film.


Drifter
"I've been here, I've been there..."

Scott W wrote:

paul wrote:

One result of this effect (if I understand correctly -and I'm unsure)
is that an unmanipulated RAW image looks too dark & muddy. Most of the
information is crammed in the highlights. A curve needs to be applied
to the image to increase contrast back to what our non-linear eyes
expect to see.


The raw file holds the light values for the pixel in a linear format,
the normal jpg format is going to hold the data in a non-linear format
to fit more dynamic range in the 8 bits. This is done with the gamma of
the image, the light level is proportional to the pixel level raised to
the gamma power. A common gamma that is used is 2.2, this is what
photos that are in the sRGB color space use. This also turns out to be
the gamma of most PC monitors, MACs use a lower number of 1.8.

So it has nothing to do with our non-linear eye and everything to do
with our non-linear monitors.


I didn't get all of what you are saying but I was reading some other
articles about a way of converting RAW in a linear format to 16 bit TIF.
Done that way, the image looks almost pure black but when curves are
applied, it can be adjusted to get more info out of high contrast
images, less blown highlights. The thing is it usually messes up the
colors so the technique is to make a B&W image with the linear
conversion then do another normal one for color & merge the two.

I think Dave is on to something about the logarithmic scale of stops
versus linear digital capture though that seems such an extreme
difference. Probably it has more to do with that than my bell curve
histogram idea.

jim evans wrote:

On Sat, 26 Feb 2005 10:41:49 -0500, Drifter
wrote:


On Fri, 25 Feb 2005 10:16:37 -0600, jim evans
wrote:


I Don't Understand Luminous Landscape "Expose Right" Article

----snip----

If you reply please do so as requested in my question to Reichmann.
That is, please either agree that my "Film" column in the table is
correct, or give the 5 values that should be in the Film column.

Jim:

I don't understand why you are trying to make a comparison to film.

It has nothing to do with using film, it implies nothing about the
behavior of film. There is no connection to using film.

That article is strictly about . . . one of the quirks of using an electronic
sensor . . .


Versus what? If it's a quirk, what doesn't have this "quirk?" Film
maybe?


It's a tip on how to take advantage of 'bonus' data hidden in RAW
digital files.