From: Floyd L. Davidson on
"DRS" <drs(a)removethis.ihug.com.au> wrote:
>"Floyd L. Davidson" <floyd(a)apaflo.com> wrote in message
>news:87zl82qsmh.fld(a)apaflo.com
>> "DRS" <drs(a)removethis.ihug.com.au> wrote:
>
>[...]
>
>>> That is possible but not something for which I have evidence. My
>>> concern here was to short-circuit this increasingly hysterical
>>> subthread by demonstrating that Floyd has been tilting at windmills.
>>> Everything Doug McDonald has said about the effect on the histogram
>>> of changing the contrast setting on the 30D is borne out by the
>>> images on the page to which I linked. Since all the major DSLR
>>> manufacturers, to the best of my knowledge, derive histograms from
>>> the JPEGs then what he has described would be universally applicable.
>>
>> The web page you cited has absolutely *nothing* on it
>> that supports what you or McDonald have said. It talks
>> only about the effect of changing contrast settings on
>> the resulting JPEG image, not on the exposure or how it
>> affects camera raw data.
>
>That is because they are two different things which nobody has conflated but
>you. The images on that site show exactly what Doug McDonald claimed and
>nothing more. Of course they show nothing on the effect on exposure or on
>Raw data but that was never the claim except in your mind. You have created
>a straw man.

It may show what Doug is talking about, but it shows
that it has nothing to do with correct exposure, which
*is* the point of this discussion.

You continue to say that effect on exposure in not
significant, but the *fact* is that is the *only* thing
that would be significant. You *cannot* get more
accurate exposure without making the histogram more
accurate. Contrast settings change the shape of the
graph between the right most edge and the the left edge
*but* *do* *not* *change* *the* *location* *of* *the* *right* *edge*.

Hence if the right edge is set correctly with high
contrast or low contrast, either way it is exactly the
same exposure and neither is more accurate than the
other.

You continue to say that low contrast makes it easier to
see where the edge is, but that is only true for special
cases, and for an equal number of special cases high
contrast would make it easier!

>> The histogram images show that *no* change in exposure
>> is demonstrated, and that *logically* it is not possible
>> to improve the accuracy of the histogram.
>
>It is possible to improve the accuracy of the histogram relative to the Raw
>data and the fact that you cannot see it when it is right before your eyes
>is your problem, not ours. Those images show 5 different histograms where
>the only variable is the contrast setting. Since the exposure has not
>changed then only one of the histograms can be the most accurate relative to
>the Raw image. It happens to be the -4 setting.

All five show *exactly* the same exposure. I assume you
are looking at the large peaks of the graph as they move
more towards the right edge. That of course is *not* a
measure of exposure.

If the graphs were designed to show the effect they
would also have to show histograms for some lower
exposure and at some higher exposure, to demonstrate
what one has to adjust for.

>
>[...]
>
>> What it does show is that the peaks in the graph get
>> moved around, and if you *mistakenly* believe that where
>> the peak is at is related to exposure, you will
>> mistakenly think that contrast has somehow helped.
>
>Straw man. All five histograms have different right-edges, indicating
>different possibilities for exposure compensation before clipping occurs.
>One of the 5 most accurately indicates the true feasible extent of ETTR, and
>that one is the -4 histogram. That is all that has been claimed.

They all have exactly the same right edge, to the degree
that it can be determined (which is exceedingly
difficult because the images were designed purposely to
de-emphasize that and to emphasize the changes that
contrast actually does cause. That of course is
perfectly reasonable because that is the topic they are
discussing, and is the reason they do not mention
exposure at all.

>> The problem with saying that contrast adjustments make
>> it more obvious where the right edge of the graph is at
>> is that different setting help or hinder with different
>> types of scenes. For one scene you might well be right
>> that it is easier to see with low contrast, but just the
>> same for the next scene you shoot it could be high
>> contrast that would help. It is *not* inherently better
>> for all purposes when set to low contrast!
>
>The question of when ETTR is suitable is a different question again., and is
>not something I addressed.

The above has nothing at all to do with suitability of
ETTR, it is not something I've addressed either. Why
are you?

>> Showing that it helps to see the edge in one condition
>> without being aware that the condition is a special
>> case, leads to a logically invalid conclusion.
>
>You are really not in any position to lecture on logic.

Other than I use it, and you don't? Seems like a good
position...

--
Floyd L. Davidson <http://www.apaflo.com/floyd_davidson>
Ukpeagvik (Barrow, Alaska) floyd(a)apaflo.com
From: Mike Russell on
On Mon, 05 Oct 2009 15:23:57 -0800, Floyd L. Davidson wrote:

[re film's "expose for shadows", digital's "expose for the highlights"]
> Actually, since film is a negative, the two are in fact
> actually the same. Expose for the brightest range of the
> *recording* *mechanism*.
>
> That just happens to be the dark areas of a scene with
> film (where the negative is clear) and the bright areas
> of a scene with an electronic sensor (the highest
> voltage output).

No - both refer to areas of the scene. The full rule of thumb for film is
"Expose for the shadows. Develop for the highlights". Exposing for the
shadows establishes the area of minimum negative density, and development
has a much greater effect on the highlights than the shadows.

For digital, exposing for the highlights amounts to playing chicken with
the brightest significant information in the image, by choosing an exposure
and ISO that puts the brightest significant subject material as close as
possible to the max sensor value, without actually losing information.

Your other points are technically true, but belie the fact that film's
Achilles heel is loss of subject shadow detail, while digital's is loss of
subject highlight detail.
<snip>
--
Mike Russell - http://www.curvemeister.com
From: Floyd L. Davidson on
Mike Russell <groupsRE(a)MOVEcurvemeister.com> wrote:
>On Mon, 05 Oct 2009 15:23:57 -0800, Floyd L. Davidson wrote:
>
>[re film's "expose for shadows", digital's "expose for the highlights"]
>> Actually, since film is a negative, the two are in fact
>> actually the same. Expose for the brightest range of the
>> *recording* *mechanism*.
>>
>> That just happens to be the dark areas of a scene with
>> film (where the negative is clear) and the bright areas
>> of a scene with an electronic sensor (the highest
>> voltage output).
>
>No - both refer to areas of the scene. The full rule of thumb for film is
>"Expose for the shadows. Develop for the highlights". Exposing for the
>shadows establishes the area of minimum negative density, and development
>has a much greater effect on the highlights than the shadows.
>
>For digital, exposing for the highlights amounts to playing chicken with
>the brightest significant information in the image, by choosing an exposure
>and ISO that puts the brightest significant subject material as close as
>possible to the max sensor value, without actually losing information.
>
>Your other points are technically true, but belie the fact that film's
>Achilles heel is loss of subject shadow detail, while digital's is loss of
>subject highlight detail.
><snip>

Interesting way to say, "No, you are right."

--
Floyd L. Davidson <http://www.apaflo.com/floyd_davidson>
Ukpeagvik (Barrow, Alaska) floyd(a)apaflo.com
From: Floyd L. Davidson on
"DRS" <drs(a)removethis.ihug.com.au> wrote:
>"Floyd L. Davidson" <floyd(a)apaflo.com> wrote in message
>news:87vdiqqqso.fld(a)apaflo.com
>> Contrast settings change the shape of the
>> graph between the right most edge and the the left edge
>> *but* *do* *not* *change* *the* *location* *of* *the* *right* *edge*.
>
>Yes, they do. Everybody sees it except you. Increase the contrast setting
>and the histogram expands left and right. Decrease contrast and the edges
>shift inwards especially on the right edge. The change in the location of
>the right edge between -4 and +4 stands out like dog's balls.

....

>>> It is possible to improve the accuracy of the histogram relative to
>>> the Raw data and the fact that you cannot see it when it is right
>>> before your eyes is your problem, not ours. Those images show 5
>>> different histograms where the only variable is the contrast
>>> setting. Since the exposure has not changed then only one of the
>>> histograms can be the most accurate relative to the Raw image. It
>>> happens to be the -4 setting.
>>
>> All five show *exactly* the same exposure.
>
>That is not in dispute. If you payed attention you'd have noticed that in
>that very paragraph I said, "Since the exposure has not changed..." The
>fact that the exposure is the same is necessary to the point being made,
>which is that changing one and only one variable, the contrast setting,
>changes the accuracy of the histogram upon which decisions about exposure
>are *subsequently* made.

You can't have it both ways. First you say that the
contrast setting moves the histogram's indication of
exposure, and now you say it does not.

All five of those histograms show *exactly* the same
exposure, even though they have 5 different contrast
settings.

If that is the desired exposure, not one of those
histograms would suggest that the camera's exposure
should be changed to be more accurate.

>> They all have exactly the same right edge, to the degree
>> that it can be determined (which is exceedingly
>
>No, they don't. Blind Freddy can see the right-edges shift by at least 1
>stop from -4 to +4, and probably more.

You apparently are looking at that huge peak value to
the left of the right edge, as it is the only thing that
moves by "at least 1 stop". But that peak has *nothing*
to do with setting correct exposure. See the little
itty bitty value down in the lower right hand corner?

That is the value of significance. That is the "right
edge".

>>> You are really not in any position to lecture on logic.
>>
>> Other than I use it, and you don't? Seems like a good
>> position...
>
>The proof is in the pudding is in the eating.

Cute. I'll settle for being logical.

--
Floyd L. Davidson <http://www.apaflo.com/floyd_davidson>
Ukpeagvik (Barrow, Alaska) floyd(a)apaflo.com
From: DRS on
"Floyd L. Davidson" <floyd(a)apaflo.com> wrote in message
news:87eipeqnt0.fld(a)apaflo.com
> "DRS" <drs(a)removethis.ihug.com.au> wrote:

[...]

>> That is not in dispute. If you payed attention you'd have noticed
>> that in that very paragraph I said, "Since the exposure has not
>> changed..." The fact that the exposure is the same is necessary to
>> the point being made, which is that changing one and only one
>> variable, the contrast setting, changes the accuracy of the
>> histogram upon which decisions about exposure are *subsequently*
>> made.
>
> You can't have it both ways. First you say that the
> contrast setting moves the histogram's indication of
> exposure, and now you say it does not.

I have always said it changes the indication of exposure. It is you who
made the false claim that I and others were saying it had anything to do
with changing the actual exposure, which we have repeatedly denied.

> All five of those histograms show *exactly* the same
> exposure, even though they have 5 different contrast
> settings.

And because of the different contrast settings the 5 histograms show the
exposure differently. The exposure hasn't changed but the accuracy of its
representation has. Which is all that has been claimed.

> If that is the desired exposure, not one of those
> histograms would suggest that the camera's exposure
> should be changed to be more accurate.

None of the 5 histograms indicate overexposure. What they do indicate, to
different degrees of accuracy, is the room for exposure compensation. Only
1 can be the most accurate and it is the -4 histogram.

[...]

>> No, they don't. Blind Freddy can see the right-edges shift by at
>> least 1 stop from -4 to +4, and probably more.
>
> You apparently are looking at that huge peak value to
> the left of the right edge, as it is the only thing that
> moves by "at least 1 stop". But that peak has *nothing*
> to do with setting correct exposure. See the little
> itty bitty value down in the lower right hand corner?
>
> That is the value of significance. That is the "right
> edge".

In this instance that indicates specular highlights, which as has been noted
by several people, may be blown without spoiling the image. That is a
choice by the photographer.

[...]

>> The proof is in the pudding is in the eating.
>
> Cute. I'll settle for being logical.

Good. I hope to see it soon.