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-   -   Re: he histogram as the basis of automatic exposure. (http://www.velocityreviews.com/forums/t955362-re-he-histogram-as-the-basis-of-automatic-exposure.html)

Chris Malcolm 12-11-2012 11:23 AM

Re: he histogram as the basis of automatic exposure.
 
Eric Stevens <eric.stevens@sum.co.nz> 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 12-13-2012 10:34 AM

Re: he histogram as the basis of automatic exposure.
 
Gary Eickmeier <geickmei@tampabay.rr.com> wrote:
> "Chris Malcolm" <cam@holyrood.ed.ac.uk> wrote in message
> news:aioje4Fnb8oU5@mid.individual.net...


>> 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.


No, firstly because it's not perfect, secondly because sometimes it's
an aesthetic decision about what is a bad histogram for your
particular purposes, and thirdly because it's always possible for you
to have instructed the camera to adjust the exposure in some way.

Two things that I spend quite a lot of learning about with any new
model of camera are when it's likely to get the exposure wrong, and
when it's likely to get the focus wrong. I tend to upgrade camera
every few years, and so far with each upgrade I've found the
autoexposure improved, and with most (but not all) I've found the
autofocus improved.

--
Chris Malcolm

Anthony Polson 12-14-2012 03:25 AM

Re: he histogram as the basis of automatic exposure.
 
Eric Stevens <eric.stevens@sum.co.nz> wrote:
>On 13 Dec 2012 10:34:25 GMT, Chris Malcolm <cam@holyrood.ed.ac.uk>
>wrote:
>
>>Two things that I spend quite a lot of learning about with any new
>>model of camera are when it's likely to get the exposure wrong, and
>>when it's likely to get the focus wrong. I tend to upgrade camera
>>every few years, and so far with each upgrade I've found the
>>autoexposure improved, and with most (but not all) I've found the
>>autofocus improved.

>
>Do you go about it systematically, or do you learn as you go?
>
>How long does it take you to familiarise yourself with a new camera?



If Chris Malcolm is the same person who posts on the Micro 4/3 Forum,
who also hails from Edinburgh, he appears to have changed his camera
four or five times in a two month period in 2012. That included
selling one camera because he disliked it then buying an identical one
only a couple of weeks later because he decided he liked it.

Apologies if it is a case of mistaken identity.



Chris Malcolm 12-15-2012 11:55 AM

Re: he histogram as the basis of automatic exposure.
 
Eric Stevens <eric.stevens@sum.co.nz> wrote:
> On 13 Dec 2012 10:34:25 GMT, Chris Malcolm <cam@holyrood.ed.ac.uk>
> wrote:


>>Two things that I spend quite a lot of learning about with any new
>>model of camera are when it's likely to get the exposure wrong, and
>>when it's likely to get the focus wrong. I tend to upgrade camera
>>every few years, and so far with each upgrade I've found the
>>autoexposure improved, and with most (but not all) I've found the
>>autofocus improved.


> Do you go about it systematically, or do you learn as you go?


I tend to learn as I go, supplemented by occasional episodes of
systematic carefully designed experiment to nail down something.

> How long does it take you to familiarise yourself with a new camera?


I guess it takes about a week, and a few reads through the manual, to
get the general hang of the obvious features and adapt my existing
habits to the new camera. It probably takes a month before I can
reliably shoot as good shots as fast I can with the old one. Of course
in some cases the new camera has features which means some kinds of
shots are now easier and faster than the old camera almost
immediattely. For example better manual focusing aids.

A new camera which has lots of new features compared to the old will
probably take me six months to discover most of the useful ones and
develop new habits to incorporate them. Then during very vaguely the
next year I'll stumble across, or have pointed out to me, certain
features or tricks which I hadn't realised existed or had mistakenly
thought were pointless to me are actually very useful in certain
special circumstances.

--
Chris Malcolm

Chris Malcolm 12-15-2012 12:10 PM

Re: he histogram as the basis of automatic exposure.
 
Anthony Polson <docnews2011@gmail.com> wrote:
> Eric Stevens <eric.stevens@sum.co.nz> wrote:
>>On 13 Dec 2012 10:34:25 GMT, Chris Malcolm <cam@holyrood.ed.ac.uk>
>>wrote:
>>
>>>Two things that I spend quite a lot of learning about with any new
>>>model of camera are when it's likely to get the exposure wrong, and
>>>when it's likely to get the focus wrong. I tend to upgrade camera
>>>every few years, and so far with each upgrade I've found the
>>>autoexposure improved, and with most (but not all) I've found the
>>>autofocus improved.

>>
>>Do you go about it systematically, or do you learn as you go?
>>
>>How long does it take you to familiarise yourself with a new camera?


> If Chris Malcolm is the same person who posts on the Micro 4/3 Forum,
> who also hails from Edinburgh, he appears to have changed his camera
> four or five times in a two month period in 2012. That included
> selling one camera because he disliked it then buying an identical one
> only a couple of weeks later because he decided he liked it.


Mope, don't post on the micro 4/3 forum. Always use my real name
everywhere in cyberspace, always have since before the web was
invented.

The only times I've upgraded cameras more frequently than once every
three years have been when I've seriously broken one, and had to
factor a large repair bill into the cost of upgrade equation.

Latest camera is Sony A77, bought 2nd hand several weeks ago 3 years
after Sony A550.

--
Chris Malcolm

Chris Malcolm 12-17-2012 11:31 AM

Re: he histogram as the basis of automatic exposure.
 
Chris Malcolm <cam@holyrood.ed.ac.uk> wrote:
> Anthony Polson <docnews2011@gmail.com> wrote:
>> Eric Stevens <eric.stevens@sum.co.nz> wrote:
>>>On 13 Dec 2012 10:34:25 GMT, Chris Malcolm <cam@holyrood.ed.ac.uk>
>>>wrote:
>>>
>>>>Two things that I spend quite a lot of learning about with any new
>>>>model of camera are when it's likely to get the exposure wrong, and
>>>>when it's likely to get the focus wrong. I tend to upgrade camera
>>>>every few years, and so far with each upgrade I've found the
>>>>autoexposure improved, and with most (but not all) I've found the
>>>>autofocus improved.
>>>
>>>Do you go about it systematically, or do you learn as you go?
>>>
>>>How long does it take you to familiarise yourself with a new camera?


>> If Chris Malcolm is the same person who posts on the Micro 4/3 Forum,
>> who also hails from Edinburgh, he appears to have changed his camera
>> four or five times in a two month period in 2012. That included
>> selling one camera because he disliked it then buying an identical one
>> only a couple of weeks later because he decided he liked it.


> Mope, don't post on the micro 4/3 forum. Always use my real name
> everywhere in cyberspace, always have since before the web was
> invented.


> The only times I've upgraded cameras more frequently than once every
> three years have been when I've seriously broken one, and had to
> factor a large repair bill into the cost of upgrade equation.


> Latest camera is Sony A77, bought 2nd hand several weeks ago 3 years
> after Sony A550.


Did a bit of googling and looks like I may have bought that camera
from the chap you're talking about who has been doing a lot of recent
buying and selling of cameras and lenses. We don't know each other,
and only met in the context of the sale.

--
Chris Malcolm


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