In camera histogram - raw vs jpg and exposure

Archived from groups: rec.photo.digital (More info?)

"Brian" <ripcurl187@yahoo.com> writes:

> I was reading this article regarding exposure strategies for raw and
> jpg images, but I don't fully understand some of the things that are
> mentioned...
>
> http://visual-vacations.com/Photography/exposure_meteri...
>
>>From the section "Using The Histogram To Properly Judge Exposure"
> 1. why do spikes at the right side of the raw histogram (even when
> they're not touching the right edge) indicate clipped raw data when you
> can't bring them down with major exposure adjustments (down)? (as shown
> in the sample histogram - "ACR Clipped RAW Histogram")

A spike *right at* 255 is either clipped data, or else the
*remarkable* coincidence of a suddenly much greater number of pixels
honestly at brightness 255, and I know which way *I'm* betting.

The other thing to remember, though, is that specular reflections may
legitemately clip. There's no data there anyway.
--
David Dyer-Bennet, <mailto d-b@dd-b.net>, <http://www.dd-b.net/dd-b/&gt;
RKBA: <http://noguns-nomoney.com/&gt; <http://www.dd-b.net/carry/&gt;
Pics: <http://dd-b.lighthunters.net/&gt; <http://www.dd-b.net/dd-b/SnapshotAlbum/&gt;
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Archived from groups: rec.photo.digital (More info?)

In message <1106098523.517305.96690@f14g2000cwb.googlegroups.com>,
"Brian" <ripcurl187@yahoo.com> wrote:

>I was reading this article regarding exposure strategies for raw and
>jpg images, but I don't fully understand some of the things that are
>mentioned...
>
>http://visual-vacations.com/Photography/exposure_meteri...
>
>>From the section "Using The Histogram To Properly Judge Exposure"
>1. why do spikes at the right side of the raw histogram (even when
>they're not touching the right edge) indicate clipped raw data when you
>can't bring them down with major exposure adjustments (down)? (as shown
>in the sample histogram - "ACR Clipped RAW Histogram")

In ACR, clipped data does not come down past the right edge of the
histogram. This is kind of annoying if you're over-exposing on purpose,
to get better shadows. It seems to nail 4095 to the right edge when it
would otherwise come to the left of it, and stretch the brightest
highlights over a wide range.

>2. when comparing the histogram from the jpg image and the raw image
>(in photoshop elements 3 or CS), should the raw file be converted
>first? if so, what settings should be used? if i use the 'default
>camera settings' for my camera (canon g2), ACR adjusts exposure down by
>1.3 stops which obviously leaves a lot more room on the right side of
>the histogram.

?
--

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John P Sheehy <JPS@no.komm>
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