From: ray on
On Mon, 01 Sep 2008 05:40:18 +0000, David J Taylor wrote:

> Alan Browne wrote:
> []
>> JPG's 8 bits/color is compressed DR, not more DR. The 'loss' is in
>> graduation 'tween colors. JPG cannot contain an expression of more
>> information than the original raw, compressed or otherwise.
>>
>> The key point is that in-camera JPG leaves you with much less in terms
>> of options than post-processed raw.
>
> With an 8-bit linear coding, the ratio between maximum and minimum
> signal level is 255:1.
>
> The typical RAW data is 12-bit or 14-1bit, having a ratio of max/min of
> 4095:1 or 16383:1.
>
> With JPEG, taking 2.2 as the typical gamma correction, the ratio is
> 255^2.2:1, or about 200,000:1.
>
> Agreed that JPEG compromises on the accuracy with which any particular
> brightness can be represented, but the range of values which can be
> represented is greater with JPEG than RAW.
>
> Cheers,
> David

Since, as I understand it, a RAW file is basically a dump of the sensor
data, you can't do any better than that. Theoretical limitations are one
thing - practical applications are another.
From: Alan Browne on
David J Taylor wrote:
> Alan Browne wrote:
> []
>> JPG's 8 bits/color is compressed DR, not more DR. The 'loss' is in
>> graduation 'tween colors. JPG cannot contain an expression of more
>> information than the original raw, compressed or otherwise.
>>
>> The key point is that in-camera JPG leaves you with much less in terms
>> of options than post-processed raw.
>
> With an 8-bit linear coding, the ratio between maximum and minimum signal
> level is 255:1.
>
> The typical RAW data is 12-bit or 14-1bit, having a ratio of max/min of
> 4095:1 or 16383:1.
>
> With JPEG, taking 2.2 as the typical gamma correction, the ratio is
> 255^2.2:1, or about 200,000:1.

I take your point, however, there can not be more _information_ there,
there can only be less. The raw file contains all the information
required to make a file equivalent to the JPG. Regardless of encoding
and representation.

> Agreed that JPEG compromises on the accuracy with which any particular
> brightness can be represented, but the range of values which can be
> represented is greater with JPEG than RAW.

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From: David J Taylor on
Robert Coe wrote:
> On Mon, 01 Sep 2008 05:42:50 GMT, "David J Taylor"
> <david-taylor(a)blueyonder.neither-this-bit.nor-this-part.co.uk> wrote:
>> John McWilliams wrote:
>> []
>>> I am not familiar with either camera, but in any event, it's
>>> irrelevant to my statement: JPEGs do not have inherently more
>>> dynamic range than the RAW from which it's processed.
>>
>> Of course not, but on its own, JPEG has the greater dynamic range.
>> See my earlier post for the numbers.
>
> But no camera currently in production captures more information for
> its JPEGs than for its RAW images, right? So what practical
> difference does JPEG's theoretically greater dynamic range make?
>
> Bob

Well, if you recall, someone stated, and I paraphrase, that "JPEGs are
8-bit but RAW is 12-bit", and it's that blunt statement which does not
tell the whole story.

David


From: David J Taylor on
ray wrote:
[]
> Since, as I understand it, a RAW file is basically a dump of the
> sensor data, you can't do any better than that. Theoretical
> limitations are one thing - practical applications are another.

However, the simple statement that "RAW is 12-bit and JPEG is 8-bit, so
JPEG can't have the same dynamic range" is incorrect, and that's what the
maths showed.

David


From: John McWilliams on
Shon Kei Picture company wrote:
> John McWilliams wrote:
>> David J Taylor wrote:
>>> John McWilliams wrote:
>>> []
>>>> RAW files can be converted to a viewable format by non-linear or
>>>> linear, gamma corrected, or not, depending on the software and
>>>> settings of the user.
>>>>
>>>> Saying JPEGs have more dynamic range is simply wrong.
>>>
>>> To clarify, John, I was talking about the JPEG files which come
>>> straight from the camera, not those from a RAW to JPEG conversion.
>>>
>>> Given the class of camera under consideration (Fuji F100fd and Nikon
>>> Coolpix 610), would you like to name one which uses a linear rather
>>> than a gamma corrected representation in the JPEG? I would be very
>>> surprised if any did.
>>
>> I am not familiar with either camera, but in any event, it's
>> irrelevant to my statement: JPEGs do not have inherently more dynamic
>> range than the RAW from which it's processed.
>>
>
> It's not your misunderstanding of a camera's dynamic range that matters
> as much as whether or not you can display it all in a single picture.

<< Snipped bits out >>

While some of what I snipped I agree with, some disagree, it's all
irrelevant to the simple point I made which some fail to grasp:

The dynamic range of a JPEG cannot be greater than the RAW file from
which it's produced, unless it's a matter of poor processing of said RAW.

--
john mcwilliams