From: Elliott Roper on
In article <251020091704223902%nospam(a)yrl.co.uk>, Elliott Roper
<nospam(a)yrl.co.uk> wrote:

> In article <hr4er6-qo4.ln1(a)ID-52418.user.berlin.de>, Wolfgang
> Weisselberg <ozcvgtt02(a)sneakemail.com> wrote:
<snip>
> RAW gives me 14 bits/channel to play with later. 128 times better than
> the first jpg the camera thought of. Why throw away all that
> post-processing fun?.
Damn! Would you make that 64 times?

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From: David J Taylor on

"Elliott Roper" <nospam(a)yrl.co.uk> wrote in message
news:251020091722309218%nospam(a)yrl.co.uk...
> In article <251020091704223902%nospam(a)yrl.co.uk>, Elliott Roper
> <nospam(a)yrl.co.uk> wrote:
>
>> In article <hr4er6-qo4.ln1(a)ID-52418.user.berlin.de>, Wolfgang
>> Weisselberg <ozcvgtt02(a)sneakemail.com> wrote:
> <snip>
>> RAW gives me 14 bits/channel to play with later. 128 times better than
>> the first jpg the camera thought of. Why throw away all that
>> post-processing fun?.
> Damn! Would you make that 64 times?

Except that the JPEG contains gamma-corrected data, with a greater
white-black dynamic range than 14-bit raw, albeit at a reduced brightness
accuracy, so you aren't actually comparing like with like.

Cheers,
David

From: Elliott Roper on
In article <yg0Fm.1544$5w5.535(a)text.news.virginmedia.com>, David J
Taylor <david-taylor(a)blueyonder.not-this-bit.nor-this.co.uk.invalid>
wrote:

> "Elliott Roper" <nospam(a)yrl.co.uk> wrote in message
> news:251020091722309218%nospam(a)yrl.co.uk...
> > In article <251020091704223902%nospam(a)yrl.co.uk>, Elliott Roper
> > <nospam(a)yrl.co.uk> wrote:
> >
> >> In article <hr4er6-qo4.ln1(a)ID-52418.user.berlin.de>, Wolfgang
> >> Weisselberg <ozcvgtt02(a)sneakemail.com> wrote:
> > <snip>
> >> RAW gives me 14 bits/channel to play with later. 128 times better than
> >> the first jpg the camera thought of. Why throw away all that
> >> post-processing fun?.
> > Damn! Would you make that 64 times?
>
> Except that the JPEG contains gamma-corrected data, with a greater
> white-black dynamic range than 14-bit raw, albeit at a reduced brightness
> accuracy, so you aren't actually comparing like with like.

How can that possibly be so? Where does it get the information from?
And where does it put it? Scrunching it up on a log curve is neat, but
it still does not invent dynamic range from thin air.

I can sure push RAW around in post far more than I can push a jpg. So
the gamma correction does not seem to be delivering even that much.

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From: David J Taylor on
"Elliott Roper" <nospam(a)yrl.co.uk> wrote in message
news:251020091802112035%nospam(a)yrl.co.uk...
[]
> How can that possibly be so? Where does it get the information from?
> And where does it put it? Scrunching it up on a log curve is neat, but
> it still does not invent dynamic range from thin air.
>
> I can sure push RAW around in post far more than I can push a jpg. So
> the gamma correction does not seem to be delivering even that much.

Yes, as I said although the dynamic range is greater (it's about
200,000:1) in a pure gamma-corrected JPEG, the accuracy is much less. At
the low end the lowest value 1 is 1/200,000 full scale, and the next value
is 1/50,000 full scale. Similarly at the high end the difference between
254 and 255 is 1%, rather than the 0.4% you might expect.

The gamma correction delivers you data, which is adequate for a human to
view under typical conditions, in a more compact form.

Cheers,
David

From: Elliott Roper on
In article <hy2Fm.1571$5w5.557(a)text.news.virginmedia.com>, David J
Taylor <david-taylor(a)blueyonder.not-this-bit.nor-this.co.uk.invalid>
wrote:

> "Elliott Roper" <nospam(a)yrl.co.uk> wrote in message
> news:251020091802112035%nospam(a)yrl.co.uk...
> []
> > How can that possibly be so? Where does it get the information from?
> > And where does it put it? Scrunching it up on a log curve is neat, but
> > it still does not invent dynamic range from thin air.
> >
> > I can sure push RAW around in post far more than I can push a jpg. So
> > the gamma correction does not seem to be delivering even that much.
>
> Yes, as I said although the dynamic range is greater (it's about
> 200,000:1) in a pure gamma-corrected JPEG, the accuracy is much less. At
> the low end the lowest value 1 is 1/200,000 full scale, and the next value
> is 1/50,000 full scale. Similarly at the high end the difference between
> 254 and 255 is 1%, rather than the 0.4% you might expect.
>
> The gamma correction delivers you data, which is adequate for a human to
> view under typical conditions, in a more compact form.

I still don't get it. If the camera is detecting 14 bits per channel,
that's a dynamic range of 2^14 == 1/16384 per channel. Where are the
other 3.61 bits coming from?
I'll accept that if you had 'em in the first place, you could trade
accuracy for range, as you scrunch down to 8 bits, but the camera's
internal jpg processor is only given 14 bits to play with.

As a general rule, the camera's un-informed first guess at a jpg is
pants, and with the compressed pile of bits it hands back, you are
stuck with it.

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