From: Wilba on
Porte Rouge wrote:
>
> I set my exposure to slide the histogram to the right, without clipping
> ( when I have time), to capture the most tonal levels . So, now when I
> am editing the photos they are over exposed(not clipped). A sunrise is
> a good example. The deep colors are washed out. The obvious fix(to me
> anyway) in Lightroom or CS4 is to reduce the exposure. Now my question
> is, by reducing exposure in post, am I just ending up in the same place
> (histogram to the left) as if I had just ignored the histogram when I
> was shooting and set the exposure to properly expose the image using
> my light meter? I guess in short I am asking if Lightroom or CS4 loses
> tonal values when you reduce exposure in editing.

Yes, reducing the exposure in Lightroom just puts your histogram back to the
left, so that's a waste of time. To avoid having the deep colours washed
out, you need to make use of the full tonal range available in the image. If
you have done a good job of exposing to the right, your highlights will be
pretty much where they need to be. So then all you need to do is raise the
black point (e.g. using the Levels dialog in Photoshop), so that the dark
tones in the scene end up as dark tones in the image. If you are using the
Levels dialog in Photoshop, while you drag the black (or white) point
slider, press the Alt key to see which pixels are clipped (or blown).

(The following relates to my experience with a Canon 450D. YMMV.)

There are two parts to exposing to the right - levels in the image and
saturation of photosites. Whether you are shooting JPEG or raw, the camera's
histogram display shows you the levels in a JPEG produced from the raw data,
so the shape of the histogram curve depends on your settings for sharpness,
contrast, saturation, colour tone, etc.

If you are shooting JPEG, all you can do is avoid piling up the histogram on
the right, which prevents gross areas of blown highlights in the image.

If you are shooting raw, you can overexpose (beyond the point at which the
histogram curve touches the right boundary), by about two steps and still
produce an image from the raw without blown highlights. IOW, the headroom
between blown highlights in the JPEG and saturation of the photosites is
about two steps (in my experience, with the JPEG settings I use).

So if you are bracketing for the best possible exposure, go at least two
steps over what the histogram tells you is "correct". The maximum possible
dynamic range occurs at the point where photosites in the highlights begin
to saturate.

In everyday raw shooting, you can be quite relaxed about having a small
spike on the right of the histogram - that's actually a good thing.


From: Wilba on
Floyd L. Davidson wrote:
> Charles wrote:
>>
>> For me, digital is the opposite of film in exposure emphasis.
>> In film, you expose for the shadows, while in digital you should
>> 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).

That's a great way to say it. Thanks for that.


From: Floyd L. Davidson on
"Wilba" <usenet(a)CUTTHISimago.com.au> wrote:
>Porte Rouge wrote:
>>
>> I set my exposure to slide the histogram to the right, without clipping
>> ( when I have time), to capture the most tonal levels . So, now when I
>> am editing the photos they are over exposed(not clipped). A sunrise is
>> a good example. The deep colors are washed out. The obvious fix(to me
>> anyway) in Lightroom or CS4 is to reduce the exposure. Now my question
>> is, by reducing exposure in post, am I just ending up in the same place
>> (histogram to the left) as if I had just ignored the histogram when I
>> was shooting and set the exposure to properly expose the image using
>> my light meter? I guess in short I am asking if Lightroom or CS4 loses
>> tonal values when you reduce exposure in editing.
>
>Yes, reducing the exposure in Lightroom just puts your histogram back to the
>left, so that's a waste of time.

Yes for the histogram, but it is not a waste of time.

Increasing the exposure adds signal, but the noise stays
the same. In other words, if you take a shot of an
object that is all grey, with nothing approaching
"white" at all in the entire scene, you could

1) Expose to produce an histogram that matches
the scene, showing all values to be in the
middle of the graph. This will produce an
accurately exposed JPEG too.

or,

2) Expose to produce an histogram with the data
pushed so far to the right that it is almost,
but not quite, clipping. The JPEG produce
will be "overexposed", and instead of grey
the scene will be white.

But we want an image made from the camera raw data, not
the JPEG. And note that with either of the above
methods the "noise" in the data will be the same. The
Signal to Noise Ratio (SNR) for method #2 will be higher
because the signal is higher.

The final image is made using the RAW converter, or an
image editor like Photoshop after conversion, to reduce
the whites down to grey. And the same process will
*equally* reduce the noise. Thus the noise in the final
image will be *lower* with method 2 than with method 1.

Reducing the amount of noise in the final product is
probably *not* a waste of time.

--
Floyd L. Davidson <http://www.apaflo.com/floyd_davidson>
Ukpeagvik (Barrow, Alaska) floyd(a)apaflo.com
From: Paul Furman on
Floyd L. Davidson wrote:
> Paul Furman <paul-@-edgehill.net> wrote:
>> Floyd L. Davidson wrote:
>>> Doug McDonald <mcdonald(a)NoSpAmscs.uiuc.edu> wrote:
>>>> Floyd L. Davidson wrote:
>>>>
>>>>> 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! All that changing in-camera contrast
>>>>> does is compress/uncompress the histograms idea of
>>>>> middle gray. It does not change where the highlights
>>>>> fall, and thus does not change what you would set for
>>>>> the exposure. (Does anyone ever look at the shape of an
>>>>> in-camera histogram and make adjustments as a result?
>>>>> It's a meaningless excercise, which will not change the
>>>>> camera raw data. The shape of a post processing
>>>>> histogram is very useful, but not an in-camera
>>>>> histogram.)
>>>>>
>>>> What you say is wrong for the Canon 30D. The histogram does
>>>> not change the raw data stored by the camera. But the camera setting DOES
>>>> change the camera displayed histogram. IF you set the camera "comtrast"
>>>> setting high, the highlights in the histogram get pushed way up
>>>> and are indeed useless for setting exposure. Ii you set it low,
>>>> at -3 or -4, the histogram displayed by the camera agrees quite nicely
>>>> with how close you are getting to clipping.
>>> The brightest part will still show at *exactly* the
>>> same
>>> place.
>> Maybe for contrast (though I doubt it) but WB makes a big difference. I
>> just tested at 25K & 100K, the highlights are completely different. I'm
>> looking at split RGB histograms btw.
>
> 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. 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.

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.

--
Paul Furman
www.edgehill.net
www.baynatives.com

all google groups messages filtered due to spam
From: Paul Furman on
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

--
Paul Furman
www.edgehill.net
www.baynatives.com

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