From: Floyd L. Davidson on
Paul Furman <paul-@-edgehill.net> wrote:
>Floyd L. Davidson wrote:
>> Paul Furman <paul-@-edgehill.net> wrote:
>>> Floyd L. Davidson wrote:
>>>> That is exactly the point I *am* making. WB changes
>>>> the histogram in a useful way. The Luminous-Landscape
>>>> article did not talk about WB at all. They discussed
>>>> changing the camera's setting for contrast, and that
>>>> simply does *nothing* useful for the histogram/exposure
>>>> issue. And if you doubt that the contrast setting will not
>>>> change the histogram as stated, *try* *it*. I gave an step by
>>>> step description of a very easy way to show exactly what
>>>> does and does not happen. Why argue from supposition when
>>>> you could actually learn something about photography...
>>> I am interested in learning. I tried fiddling with
>>> the camera contrast
>>> settings to compare histograms and the difference was very minor, at
>>> least for the conditions I tried just now.
>
>A second try showed a significant difference.
>
>>> I was thinking of
>>> post-processing where increasing contrast blows highlights & blocks
>>> shadows. Maybe not the very final edge of 100% saturation but contrast
>>> adjustments can make a big difference in what appears to be blown or
>>> blocked. What you are describing sounds more like a gamma adjustment
>>> than contrast where only the middle part shifts.
>
>Scratch that comment, they both have an effect.
>
>> "Gamma is equivalent to contrast.
>
>I dunno, maybe your linked definers are thinking of a different context.

I would expect that both Norman Koren and HP do know exactly what
gamma and contrast are. The context is *exactly* the one we are
discussing.

>Common sense and experience tell me gamma is adjusting the middle-value,
>more like brightness, without changing the the ends.

A generalization, but not wrong.

>Contrast
>adjustments tend to hold the mid-point and use an s curve to raise
>highlights & lower shadows or the inverse.

Not true. Contrast is the slope of the curve.

>A gamma adjustment curve is a
>fairly simple bowed shape, not an s shape.

Not necessarily.

>Sure a gamma adjustment has
>an effect on contrast but that's a side effect, not the goal. Gamma
>adjustments boost contrast in either the highlights or shadows, not both.

Not necessarily.

>> This can be observed
>> in traditional film curves, which are displayed on
>> logarithmic scales (typically, density (log10(absorbed
>> light) vs. log10(exposure)). Gamma is the average
>> slope of this curve (excluding the "toe" and
>> "shoulder" regions near the ends of the curve), i.e.,
>> the contrast."
>> http://www.imatest.com/docs/glossary.html
>> (The above is a web page owned by Norman Koren.)
>> "Gamma -- A way of representing the contrast of an
>> image, shown as the slope of a curve showing tones
>> from white to black."
>> http://www.hp.com/united-states/consumer/digital_photography/articles/scanner_glossary.html
>> That might help make things clearer as to why changing
>> contrast does not make the histogram any more or less
>> accurate for exposure.
>> When the histogram indicates precisely the correct
>> exposure, changing the gamma (contrast) moves the curve
>> between black and maximum white values, but it doesn't
>> change the value of either. Note too that it might
>> spread the histogram out from the center (if the gamma
>> curve is moved by picking a point at its center), or it
>> might move towards ether the right or the left (if the
>> gamma curve is moved from point closer to the ends
>> instead of at the center).
>> In any case, it changes the contrast but if there are
>> image values at the maximum white value they will not be
>> moved.
>
>The maximum white value may be already off the edge so you are talking
>about part of the middle of the curve, which is effected, showing more
>detail with low contrast.

Maximum white values cannot go "off the edge". They go *to the edge*,
and no higher. The maximum value does not change, though the number
of pixels that have that value might change.

>>> An interesting related issue I don't understand is how the exposure
>>> slider works in Lightroom or ACR. I don't know how to duplicate that
>>> effect in photoshop with curves, levels, etc. Those all do like you
>>> describe, moving the middle parts of the histogram but there isn't an
>>> easy way I can see to shift the whole exposure. Hmm, the middle slider
>>> on levels comes close but still doesn't match the effect.
>> I don't use those programs so I can only provide
>> general
>> instructions about how that is typically done. I'll
>> leave it to someone who can be more specific.
>
>Understanding this would help in simulating exposure changes in an
>editor - to better understand when shooting & interpreting the histogram.

Yes, you will certainly find it useful.

--
Floyd L. Davidson <http://www.apaflo.com/floyd_davidson>
Ukpeagvik (Barrow, Alaska) floyd(a)apaflo.com
From: Floyd L. Davidson on
Porte Rouge <porterougeman(a)gmail.com> wrote:
>On Oct 8, 6:22�am, fl...(a)apaflo.com (Floyd L. Davidson) wrote:
>> Paul Furman <pa...@-edgehill.net> wrote:
>> >John Sheehy wrote:
>> >> Paul Furman wrote:
>>
>> >>> OK, the noise is more the reason but posterizing can
>> >>> be a problem in dark areas...
>> >> The only cameras I know of with even a hint of RAW
>> >> posterization are the Pentax K10D, which would profit
>> >> from 13 bits instead of 12 at ISO 100 (not for 200 or
>> >> higher), the Sony A900 also with a need for 13 bits at
>> >> base, and the D3X when in 12-bit mode. �These are only
>> >> on the fringe of posterizing.
>>
>> >>> raising shadows in post for the deepest shadows, and
>> >>> in skies where the color pallet is very
>> >>> limited. Doesn't the noise level follow this same
>> >>> principle? Or is there an unrelated reason for the
>> >>> noise levels paralleling tone counts?
>> >> Any posterization you see in a RAW conversion is most
>> >> likely caused by the math used in the converter, and
>> >> nothing else. �Of course, JPEG compression does some
>> >> posterization of its own, especially if you use too
>> >> much NR and it starts blocking up.
>>
>> >OK, this makes sense, the posterizing issue is not really visible in any
>> >sort of normal exposure. What about Floyd's comment below that the noise
>> >level remains the same but exposing to the right increases the signal so
>> >that overwhelms the noise? That seems to tie the two together in a
>> >comprehensible way. The LL link just makes a lot of sense, it can't be
>> >complete BS.http://www.luminous-landscape.com/tutorials/expose-right.shtml
>>
>> That is an *excellent* article. �It also has a link to
>> another article, titled "Understanding Histograms",
>> which several contributors to this thread could benefit
>> from (particularly the histogram of the moon shot and
>> the high key tree image that are the last two shown at
>> the bottom of the article):
>>
>> �http://www.luminous-landscape.com/tutorials/understanding-series/unde...
>>
>> --
>> Floyd L. Davidson <http://www.apaflo.com/floyd_davidson>
>> Ukpeagvik (Barrow, Alaska) � � � � � � �fl...(a)apaflo.com
>
>Hey, that's the same article you said this about:
>
>"But regardless of that, the cited URL above from
>luminous-landscape is *not* full of good stuff. They
>miss the point entirely, and provide nothing that is
>actually useful!"

No it is *not* the same article.

--
Floyd L. Davidson <http://www.apaflo.com/floyd_davidson>
Ukpeagvik (Barrow, Alaska) floyd(a)apaflo.com
From: Porte Rouge on
On Oct 8, 2:36 pm, fl...(a)apaflo.com (Floyd L. Davidson) wrote:
> Porte Rouge <porterouge...(a)gmail.com> wrote:
> >On Oct 8, 6:22 am, fl...(a)apaflo.com (Floyd L. Davidson) wrote:
> >> Paul Furman <pa...@-edgehill.net> wrote:
> >> >John Sheehy wrote:
> >> >> Paul Furman wrote:
>
> >> >>> OK, the noise is more the reason but posterizing can
> >> >>> be a problem in dark areas...
> >> >> The only cameras I know of with even a hint of RAW
> >> >> posterization are the Pentax K10D, which would profit
> >> >> from 13 bits instead of 12 at ISO 100 (not for 200 or
> >> >> higher), the Sony A900 also with a need for 13 bits at
> >> >> base, and the D3X when in 12-bit mode.  These are only
> >> >> on the fringe of posterizing.
>
> >> >>> raising shadows in post for the deepest shadows, and
> >> >>> in skies where the color pallet is very
> >> >>> limited. Doesn't the noise level follow this same
> >> >>> principle? Or is there an unrelated reason for the
> >> >>> noise levels paralleling tone counts?
> >> >> Any posterization you see in a RAW conversion is most
> >> >> likely caused by the math used in the converter, and
> >> >> nothing else.  Of course, JPEG compression does some
> >> >> posterization of its own, especially if you use too
> >> >> much NR and it starts blocking up.
>
> >> >OK, this makes sense, the posterizing issue is not really visible in any
> >> >sort of normal exposure. What about Floyd's comment below that the noise
> >> >level remains the same but exposing to the right increases the signal so
> >> >that overwhelms the noise? That seems to tie the two together in a
> >> >comprehensible way. The LL link just makes a lot of sense, it can't be
> >> >complete BS.http://www.luminous-landscape.com/tutorials/expose-right.shtml
>
> >> That is an *excellent* article.  It also has a link to
> >> another article, titled "Understanding Histograms",
> >> which several contributors to this thread could benefit
> >> from (particularly the histogram of the moon shot and
> >> the high key tree image that are the last two shown at
> >> the bottom of the article):
>
> >>  http://www.luminous-landscape.com/tutorials/understanding-series/unde...
>
> >> --
> >> Floyd L. Davidson <http://www.apaflo.com/floyd_davidson>
> >> Ukpeagvik (Barrow, Alaska)              fl...(a)apaflo.com
>
> >Hey, that's the same article you said this about:
>
> >"But regardless of that, the cited URL above from
> >luminous-landscape is *not* full of good stuff.  They
> >miss the point entirely, and provide nothing that is
> >actually useful!"
>
> No it is *not* the same article.
>
> --
> Floyd L. Davidson <http://www.apaflo.com/floyd_davidson>
> Ukpeagvik (Barrow, Alaska)              fl...(a)apaflo.com

This is the link in both of Paul's posts:

http://www.luminous-landscape.com/tutorials/expose-right.shtml


From: Floyd L. Davidson on
Porte Rouge <porterougeman(a)gmail.com> wrote:
>On Oct 8, 2:36�pm, fl...(a)apaflo.com (Floyd L. Davidson) wrote:
>> Porte Rouge <porterouge...(a)gmail.com> wrote:
>> >On Oct 8, 6:22�am, fl...(a)apaflo.com (Floyd L. Davidson) wrote:
>> >> Paul Furman <pa...@-edgehill.net> wrote:
>> >> >John Sheehy wrote:
>> >> >> Paul Furman wrote:
>>
>> >> >>> OK, the noise is more the reason but posterizing can
>> >> >>> be a problem in dark areas...
>> >> >> The only cameras I know of with even a hint of RAW
>> >> >> posterization are the Pentax K10D, which would profit
>> >> >> from 13 bits instead of 12 at ISO 100 (not for 200 or
>> >> >> higher), the Sony A900 also with a need for 13 bits at
>> >> >> base, and the D3X when in 12-bit mode. �These are only
>> >> >> on the fringe of posterizing.
>>
>> >> >>> raising shadows in post for the deepest shadows, and
>> >> >>> in skies where the color pallet is very
>> >> >>> limited. Doesn't the noise level follow this same
>> >> >>> principle? Or is there an unrelated reason for the
>> >> >>> noise levels paralleling tone counts?
>> >> >> Any posterization you see in a RAW conversion is most
>> >> >> likely caused by the math used in the converter, and
>> >> >> nothing else. �Of course, JPEG compression does some
>> >> >> posterization of its own, especially if you use too
>> >> >> much NR and it starts blocking up.
>>
>> >> >OK, this makes sense, the posterizing issue is not really visible in any
>> >> >sort of normal exposure. What about Floyd's comment below that the noise
>> >> >level remains the same but exposing to the right increases the signal so
>> >> >that overwhelms the noise? That seems to tie the two together in a
>> >> >comprehensible way. The LL link just makes a lot of sense, it can't be
>> >> >complete BS.http://www.luminous-landscape.com/tutorials/expose-right.shtml
>>
>> >> That is an *excellent* article. �It also has a link to
>> >> another article, titled "Understanding Histograms",
>> >> which several contributors to this thread could benefit
>> >> from (particularly the histogram of the moon shot and
>> >> the high key tree image that are the last two shown at
>> >> the bottom of the article):
>>
>> >> �http://www.luminous-landscape.com/tutorials/understanding-series/unde...
>>
>> >> --
>> >> Floyd L. Davidson <http://www.apaflo.com/floyd_davidson>
>> >> Ukpeagvik (Barrow, Alaska) � � � � � � �fl...(a)apaflo.com
>>
>> >Hey, that's the same article you said this about:
>>
>> >"But regardless of that, the cited URL above from
>> >luminous-landscape is *not* full of good stuff. �They
>> >miss the point entirely, and provide nothing that is
>> >actually useful!"
>>
>> No it is *not* the same article.
>>
>> --
>> Floyd L. Davidson <http://www.apaflo.com/floyd_davidson>
>> Ukpeagvik (Barrow, Alaska) � � � � � � �fl...(a)apaflo.com
>
>This is the link in both of Paul's posts:
>
>http://www.luminous-landscape.com/tutorials/expose-right.shtml

The article I made that comment about is entirely
different. It is by Ray Maxwell and is titled "A
Possible Problem with Expose to the Right! Or Settings
for an Accurate Histogram".

Here is a direct quote from the article I posted,
showing a distinctly different URL than the one above:

">>> http://www.luminous-landscape.com/tutorials/right-hista.shtml
>> Wow, good stuff. I had to run out and get my camera
>> and check the
...

But regardless of that, the cited URL above from
luminous-landscape is *not* full of good stuff. They"

Message-ID: <87my45th9g.fld(a)apaflo.com>
Date: Mon, 05 Oct 2009 17:58:51 -0800

--
Note that I am not using my usual signature on this
article, because you have quoted it along with the body
of text in every single exchange, which is ridiculous!
From: John McWilliams on
Clues wrote:
> On Wed, 07 Oct 2009 17:19:12 -0500, John Sheehy <JPS(a)no.komm> wrote:
>
>> Exposure to the right is usually given as advice for RAW shooting. The
>> RAW data usually clips well above the level where a JPEG would clip it,
>
> Very true, for all those cameras that intentionally do a poor job at the
> RAW to JPG conversion. This is why RAW became so popular. DSLRs are
> inherently poor at this process. In fact it's the very reason that having
> access to the RAW data became so popular. Far too many DSLR owners wanted
> to repair in their resulting images what the DSLR's firmware programmers
> failed to do correctly in the first place. Companies then realized that
> they could turn this into an asset. Not only sell a camera that didn't work
> quite right, bundled with a kit-lens that wouldn't provide images any
> better than a Barbie-Cam, conning them into buying a $5,000-$10,000 lens to
> make their $500 DSLR functional, but now also sell them expensive editing
> software to fix what their cameras weren't doing properly to provide a
> useful image right out of the box.

'Ceptin' the major camera mfg's provide software with the purchaseof the
camera, and excellent lenses can be had for a mere grand. One or two
{Nikon} may also try to sell "Pro" RAW converters.

Most in-camera conversion for JPEGs is above very decent, and is
excellent for daylight/time normal exposures.

--
john mcwilliams