From: Wilba on
Paul Furman wrote:
>
> 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.

Image | Adjustments | Exposure... ?


From: Wilba on
DRS, I really admire your patience and tolerance.

As a rule I try not to be _too_ insulting, but in this case I have to say,
Floyd, you are ASTONISHINGLY thick and childish for someone who often sounds
very intelligent. I can't recall the last time I've seen such a stupendous
display of belligerant idiocy. You really are a champ.

Ha, that feels better. Carry on.


From: Wilba on
Floyd L. Davidson wrote:
> Wilba 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.

You're the only one who has suggested otherwise. This fibre is about whether
reducing the exposure in post-processing is a good way to recover
saturation. Please pay attention to the conversation.


From: Wilba on
Porte Rouge wrote:
> Wilba 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. 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.)
>
> Aha!

:- ) Was that what you actually wanted to know?

>> 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.

And white balance, of course.

>> 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.
>
> What do you mean by steps? Do you mean stops, or steps on the aperture
> or shutter dials?

No, nothing to do with the increments by which the camera's controls change
the exposure - that's arbitrary. An exposure step is a doubling or halving
of the amount of light that reaches the sensor. A stop is a step achieved
via the aperture. Most people also say stop when they mean a step achieved
via the shutter.

> 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: Floyd L. Davidson on
"Wilba" <usenet(a)CUTTHISimago.com.au> wrote:
>Floyd L. Davidson wrote:
>> Wilba 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.
>
>You're the only one who has suggested otherwise. This fibre is about whether
>reducing the exposure in post-processing is a good way to recover
>saturation. Please pay attention to the conversation.

"Recover saturation" means what? Nobody has said any
such thing. *You* need to pay attention.

The statement (quoted above) was made that, "Yes,
reducing the exposure in Lightroom just puts your
histogram back to the left, so that's a waste of time."

That is not true. It does more than just moving the
"histogram back to the left", and what it does do is
reduce noise, which is not usually a waste of time.

--
Floyd L. Davidson <http://www.apaflo.com/floyd_davidson>
Ukpeagvik (Barrow, Alaska) floyd(a)apaflo.com