he histogram as the basis of automatic exposure.

That this is, or should be, done has been recently discussed. I though
about this while this afternoon unpacking and sorting by year a large
box of old Science Fiction magazines on a large table.

I removed the first magazine and immediately wondered where to put it.
1962: this was old but was it the oldest? How far from the left-hand
end of the table should I place it to leave room for (how many?) older
magazines?

The next one was 1975. Well, that gave some indication of the minimum
length of the line of books but, how much longer would the line grow?
It wasn't long before 1954 required that I shift everything along the
table. Soon came 1989. And so I went.

Only when I had finished did I know how many of which year that I had.

Arriving at a histogram in a camera is even worse. The range of light
values which may be detected is enormous and the histogram engine has
no way of knowing in advance of where the histogram will end up being
drawn.

The only way to determine the histogram for exposure purposes is by
taking a trial image first and determining it's histogram. But that
trial image requires that an initial exposure be determined (probably
by some form of matrix metering) followed by the taking of the trial
image. A histogram is taken from the trial image and after evaluation
it is used to adjust the initial exposure. This is then used to take
the final image.

That's an awful lot of huffing and puffing for the camera, not to
mention the shoveling of electrons and I expect only cameras of the
highest capabilities might undertake such a procedure.

I suspect that it is more likely that modern high end cameras with
more than a thousand sensing points may use these to arrive at a crude
histogram upon which the final exposure will be based. It won't be as
accurate as using a histogram from a complete image but it's going to
be a lot easier than doing it the fancy way.
--

Regards,

Eric Stevens

"Eric Stevens" wrote in message
...
That this is, or should be, done has been recently discussed. I though
about this while this afternoon unpacking and sorting by year a large
box of old Science Fiction magazines on a large table.

I removed the first magazine and immediately wondered where to put it.
1962: this was old but was it the oldest? How far from the left-hand
end of the table should I place it to leave room for (how many?) older
magazines?

The next one was 1975. Well, that gave some indication of the minimum
length of the line of books but, how much longer would the line grow?
It wasn't long before 1954 required that I shift everything along the
table. Soon came 1989. And so I went.

Only when I had finished did I know how many of which year that I had.

Arriving at a histogram in a camera is even worse. The range of light
values which may be detected is enormous and the histogram engine has
no way of knowing in advance of where the histogram will end up being
drawn.

The only way to determine the histogram for exposure purposes is by
taking a trial image first and determining it's histogram. But that
trial image requires that an initial exposure be determined (probably
by some form of matrix metering) followed by the taking of the trial
image. A histogram is taken from the trial image and after evaluation
it is used to adjust the initial exposure. This is then used to take
the final image.

That's an awful lot of huffing and puffing for the camera, not to
mention the shoveling of electrons and I expect only cameras of the
highest capabilities might undertake such a procedure.

I suspect that it is more likely that modern high end cameras with
more than a thousand sensing points may use these to arrive at a crude
histogram upon which the final exposure will be based. It won't be as
accurate as using a histogram from a complete image but it's going to
be a lot easier than doing it the fancy way.

Have you ever heard of live view?

Gary Eickmeier

In article , Gary Eickmeier says...

"Eric Stevens" wrote in message
...
That this is, or should be, done has been recently discussed. I though
about this while this afternoon unpacking and sorting by year a large
box of old Science Fiction magazines on a large table.

I removed the first magazine and immediately wondered where to put it.
1962: this was old but was it the oldest? How far from the left-hand
end of the table should I place it to leave room for (how many?) older
magazines?

The next one was 1975. Well, that gave some indication of the minimum
length of the line of books but, how much longer would the line grow?
It wasn't long before 1954 required that I shift everything along the
table. Soon came 1989. And so I went.

Only when I had finished did I know how many of which year that I had.

Arriving at a histogram in a camera is even worse. The range of light
values which may be detected is enormous and the histogram engine has
no way of knowing in advance of where the histogram will end up being
drawn.

The only way to determine the histogram for exposure purposes is by
taking a trial image first and determining it's histogram. But that
trial image requires that an initial exposure be determined (probably
by some form of matrix metering) followed by the taking of the trial
image. A histogram is taken from the trial image and after evaluation
it is used to adjust the initial exposure. This is then used to take
the final image.

That's an awful lot of huffing and puffing for the camera, not to
mention the shoveling of electrons and I expect only cameras of the
highest capabilities might undertake such a procedure.

I suspect that it is more likely that modern high end cameras with
more than a thousand sensing points may use these to arrive at a crude
histogram upon which the final exposure will be based. It won't be as
accurate as using a histogram from a complete image but it's going to
be a lot easier than doing it the fancy way.

Have you ever heard of live view?

And all non-DSLR cameras which have no separate sensor for metering are
forced to meter with the main sensor, using some sort of histogram
mechanism.
--

Alfred Molon
------------------------------
Olympus E-series DSLRs and micro 4/3 forum at
http://tech.groups.yahoo.com/group/MyOlympus/
http://myolympus.org/ photo sharing site

On Tue, 11 Dec 2012 00:56:05 -0500, "Gary Eickmeier"
wrote:


"Eric Stevens" wrote in message
.. .
That this is, or should be, done has been recently discussed. I though
about this while this afternoon unpacking and sorting by year a large
box of old Science Fiction magazines on a large table.

I removed the first magazine and immediately wondered where to put it.
1962: this was old but was it the oldest? How far from the left-hand
end of the table should I place it to leave room for (how many?) older
magazines?

The next one was 1975. Well, that gave some indication of the minimum
length of the line of books but, how much longer would the line grow?
It wasn't long before 1954 required that I shift everything along the
table. Soon came 1989. And so I went.

Only when I had finished did I know how many of which year that I had.

Arriving at a histogram in a camera is even worse. The range of light
values which may be detected is enormous and the histogram engine has
no way of knowing in advance of where the histogram will end up being
drawn.

The only way to determine the histogram for exposure purposes is by
taking a trial image first and determining it's histogram. But that
trial image requires that an initial exposure be determined (probably
by some form of matrix metering) followed by the taking of the trial
image. A histogram is taken from the trial image and after evaluation
it is used to adjust the initial exposure. This is then used to take
the final image.

That's an awful lot of huffing and puffing for the camera, not to
mention the shoveling of electrons and I expect only cameras of the
highest capabilities might undertake such a procedure.

I suspect that it is more likely that modern high end cameras with
more than a thousand sensing points may use these to arrive at a crude
histogram upon which the final exposure will be based. It won't be as
accurate as using a histogram from a complete image but it's going to
be a lot easier than doing it the fancy way.

Have you ever heard of live view?

Yep. It comes somewhere between the +1000 sensing points for metering
and a full image. Most display screens are somewhere around 850,000 to
920,000 dots which puts them way below the resolution of a 10~20Mp
image in the camera. On top of that I understand that it is common
display a simplified JPG image which is unlikely to be an accurate of
(say) the final RAW file. Still it may be possible to use the
histogram of the live view image to sharpen up the exposure on the
basis that it is better than the unadjusted output of a matrix
metering system.
--

Regards,

Eric Stevens

On Tue, 11 Dec 2012 07:57:21 +0100, Alfred Molon
wrote:

In article , Gary Eickmeier says...

"Eric Stevens" wrote in message
...
That this is, or should be, done has been recently discussed. I though
about this while this afternoon unpacking and sorting by year a large
box of old Science Fiction magazines on a large table.

I removed the first magazine and immediately wondered where to put it.
1962: this was old but was it the oldest? How far from the left-hand
end of the table should I place it to leave room for (how many?) older
magazines?

The next one was 1975. Well, that gave some indication of the minimum
length of the line of books but, how much longer would the line grow?
It wasn't long before 1954 required that I shift everything along the
table. Soon came 1989. And so I went.

Only when I had finished did I know how many of which year that I had.

Arriving at a histogram in a camera is even worse. The range of light
values which may be detected is enormous and the histogram engine has
no way of knowing in advance of where the histogram will end up being
drawn.

The only way to determine the histogram for exposure purposes is by
taking a trial image first and determining it's histogram. But that
trial image requires that an initial exposure be determined (probably
by some form of matrix metering) followed by the taking of the trial
image. A histogram is taken from the trial image and after evaluation
it is used to adjust the initial exposure. This is then used to take
the final image.

That's an awful lot of huffing and puffing for the camera, not to
mention the shoveling of electrons and I expect only cameras of the
highest capabilities might undertake such a procedure.

I suspect that it is more likely that modern high end cameras with
more than a thousand sensing points may use these to arrive at a crude
histogram upon which the final exposure will be based. It won't be as
accurate as using a histogram from a complete image but it's going to
be a lot easier than doing it the fancy way.

Have you ever heard of live view?

And all non-DSLR cameras which have no separate sensor for metering are
forced to meter with the main sensor, using some sort of histogram
mechanism.

I've wondered about these. I suspect thhe first trial shot at
measuring exposure must result in both underfilled and overflowing
pixel wells.
--

Regards,

Eric Stevens

Eric Stevens wrote:


I've wondered about these. I suspect thhe first trial shot at
measuring exposure must result in both underfilled and overflowing
pixel wells.


Have you *never* watched the live preview on a compact "hunting" for
exposure as you point the camera at darker/lighter scenes?

The very nature of a live(ish) preview mean it's
taking several "trial shots" per second, on a continuous
basis.

BugBear

Eric Stevens wrote:
That this is, or should be, done has been recently discussed. I though
about this while this afternoon unpacking and sorting by year a large
box of old Science Fiction magazines on a large table.

I removed the first magazine and immediately wondered where to put it.
1962: this was old but was it the oldest? How far from the left-hand
end of the table should I place it to leave room for (how many?) older
magazines?

The next one was 1975. Well, that gave some indication of the minimum
length of the line of books but, how much longer would the line grow?
It wasn't long before 1954 required that I shift everything along the
table. Soon came 1989. And so I went.

Only when I had finished did I know how many of which year that I had.

Arriving at a histogram in a camera is even worse. The range of light
values which may be detected is enormous and the histogram engine has
no way of knowing in advance of where the histogram will end up being
drawn.

The only way to determine the histogram for exposure purposes is by
taking a trial image first and determining it's histogram. But that
trial image requires that an initial exposure be determined (probably
by some form of matrix metering) followed by the taking of the trial
image. A histogram is taken from the trial image and after evaluation
it is used to adjust the initial exposure. This is then used to take
the final image.

That's an awful lot of huffing and puffing for the camera, not to
mention the shoveling of electrons and I expect only cameras of the
highest capabilities might undertake such a procedure.

My last three DSLRs all did histogram based autoexposure. I'd be
surprised if most reasonably good DSLRs haven't been doing it for
years. It doesn't have to done the painful way you describe. All you
need is either to have enough exposure sensors from which to derive a
useful histogram (as done by Nikon & Canon), or else a secondary
sensor such as the auxiliary live view sensor which some Sony alphas
used to have, or the permanently live main image sensor which the Sony
SLTs and NEXs have.

I suspect that it is more likely that modern high end cameras with
more than a thousand sensing points may use these to arrive at a crude
histogram upon which the final exposure will be based. It won't be as
accurate as using a histogram from a complete image but it's going to
be a lot easier than doing it the fancy way.

Which is probably why Sony have for years been doing it very
successfully another way :-)

--
Chris Malcolm

"Chris Malcolm" wrote in message
...


My last three DSLRs all did histogram based autoexposure. I'd be
surprised if most reasonably good DSLRs haven't been doing it for
years. It doesn't have to done the painful way you describe. All you
need is either to have enough exposure sensors from which to derive a
useful histogram (as done by Nikon & Canon), or else a secondary
sensor such as the auxiliary live view sensor which some Sony alphas
used to have, or the permanently live main image sensor which the Sony
SLTs and NEXs have.

I suspect that it is more likely that modern high end cameras with
more than a thousand sensing points may use these to arrive at a crude
histogram upon which the final exposure will be based. It won't be as
accurate as using a histogram from a complete image but it's going to
be a lot easier than doing it the fancy way.

Which is probably why Sony have for years been doing it very
successfully another way :-)

I haven't seen this. I have the Sony a100 and the a35, and I can easily get
a wrong exposure before I adjust it, especially with flash. Well, flash is a
separate subject, because there is no such thing as live view with flash.

But if what you say is true, that they do exposure using the histogram, then
it would be impossible to get an exposure with a bad histogram.

Eric, I would think that any histogram on a camera would be using ALL of the
pixels from the sensor, not just as many as are displayed on the LED finder.
Anyway, it gives you good enough an indication to make a perfect exposure,
in combination with being able to see the actual image!

Gary Eickmeier

In article , bugbear
says...
The very nature of a live(ish) preview mean it's
taking several "trial shots" per second, on a continuous
basis.

I believe the m4/3 cameras take 120 readings/second to quickly
autofocus. Probably the same data read from the sensor is used for
metering.
--

Alfred Molon
------------------------------
Olympus E-series DSLRs and micro 4/3 forum at
http://tech.groups.yahoo.com/group/MyOlympus/
http://myolympus.org/ photo sharing site

On Tue, 11 Dec 2012 09:58:21 +0000, bugbear
wrote:

Eric Stevens wrote:


I've wondered about these. I suspect thhe first trial shot at
measuring exposure must result in both underfilled and overflowing
pixel wells.


Have you *never* watched the live preview on a compact "hunting" for
exposure as you point the camera at darker/lighter scenes?

Nope. I've hardly ever used these things. I much prefer view finders.

The very nature of a live(ish) preview mean it's
taking several "trial shots" per second, on a continuous
basis.

' several "trial shots" per second' is raather slow in the context of
the speed of cameras I'm now used to. Mind you my old Sony 707 used to
take more than a second to take a picture after you had pushed the
button. For all of this time the view finder was blank. Panning birds
in flight was quite a lottery. :-)
--

Regards,

Eric Stevens