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Claimed high scanned film "information" is mostly garbage

 
 
John McWilliams
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      04-02-2009
user identity wrote:
> On Tue, 31 Mar 2009 11:22:35 -0400
>>
>>

> test 3



Please use a test group.
 
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John McWilliams
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      04-02-2009
David J Taylor wrote:
> John McWilliams wrote:
>> dan c. wrote:
>>> On Apr 1, 8:28 am, Kennedy McEwen <(E-Mail Removed)> wrote:

>>
>>>> Firstly, if you save both images uncompressed then the 200 ISO and
>>>> the 3200 ISO files will be exactly the same size. Ie. it is the
>>>> compression that is generating the size difference.

>>
>> This part is incorrect. Higher ISOs will have more noise, other things
>> being equal.

>
> How will having more noise affect the size on an uncompressed image?
>
> Agreed that, when compressed, a noisier image may have a larger file size.


My RAW files, as they come from the camera, are of different sizes, not
by much, but a few percentage points up or down. Are you saying camera
compression of the RAW data causes this?

--
John McWilliams




 
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David J Taylor
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      04-02-2009
John McWilliams wrote:
[]
> My RAW files, as they come from the camera, are of different sizes,
> not by much, but a few percentage points up or down. Are you saying
> camera compression of the RAW data causes this?


I was actually thinking of JPEG files but, yes, some cameras use
compression on RAW data as well. Just like the compression in Zip files,
compression /can/ be lossless.

David

 
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nospam
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      04-02-2009
In article <49d4e61d$(E-Mail Removed)>, Bob Larter
<(E-Mail Removed)> wrote:

> Yes. RAW files are losslessly compressed,


usually, but not always.
 
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Bob Larter
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      04-02-2009
John McWilliams wrote:
> David J Taylor wrote:
>> John McWilliams wrote:
>>> dan c. wrote:
>>>> On Apr 1, 8:28 am, Kennedy McEwen <(E-Mail Removed)> wrote:
>>>
>>>>> Firstly, if you save both images uncompressed then the 200 ISO and
>>>>> the 3200 ISO files will be exactly the same size. Ie. it is the
>>>>> compression that is generating the size difference.
>>>
>>> This part is incorrect. Higher ISOs will have more noise, other things
>>> being equal.

>>
>> How will having more noise affect the size on an uncompressed image?
>>
>> Agreed that, when compressed, a noisier image may have a larger file
>> size.

>
> My RAW files, as they come from the camera, are of different sizes, not
> by much, but a few percentage points up or down. Are you saying camera
> compression of the RAW data causes this?


Yes. RAW files are losslessly compressed, & the file size will increase
with increases in detail or noise.


--
W
. | ,. w , "Some people are alive only because
\|/ \|/ it is illegal to kill them." Perna condita delenda est
---^----^---------------------------------------------------------------
 
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nospam
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      04-02-2009
In article <49d4f4cb$(E-Mail Removed)>, Bob Larter
<(E-Mail Removed)> wrote:

> >> Yes. RAW files are losslessly compressed,

> >
> > usually, but not always.

>
> The formats I've seen are, but it's entirely possible there are ones
> that are uncompressed.


i was referring to lossy compressed but there's uncompressed too. nikon
offers all three variants on some cameras.
 
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Bob Larter
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      04-02-2009
nospam wrote:
> In article <49d4e61d$(E-Mail Removed)>, Bob Larter
> <(E-Mail Removed)> wrote:
>
>> Yes. RAW files are losslessly compressed,

>
> usually, but not always.


The formats I've seen are, but it's entirely possible there are ones
that are uncompressed.


--
W
. | ,. w , "Some people are alive only because
\|/ \|/ it is illegal to kill them." Perna condita delenda est
---^----^---------------------------------------------------------------
 
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Martin Brown
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      04-02-2009
John McWilliams wrote:
> David J Taylor wrote:
>> John McWilliams wrote:
>>> dan c. wrote:
>>>> On Apr 1, 8:28 am, Kennedy McEwen <(E-Mail Removed)> wrote:
>>>
>>>>> Firstly, if you save both images uncompressed then the 200 ISO and
>>>>> the 3200 ISO files will be exactly the same size. Ie. it is the
>>>>> compression that is generating the size difference.
>>>
>>> This part is incorrect. Higher ISOs will have more noise, other things
>>> being equal.

>>
>> How will having more noise affect the size on an uncompressed image?
>>
>> Agreed that, when compressed, a noisier image may have a larger file
>> size.

>
> My RAW files, as they come from the camera, are of different sizes, not
> by much, but a few percentage points up or down. Are you saying camera
> compression of the RAW data causes this?


Very likely. If it was truly pure uncompressed raw then it would be some
random header length + sensor sites*measured_bits_per_pixel/8 long every
time. Traditional raw files in the early days were one byte per sensor
pixel + header. These days some are 12bits per pixel and then losslessly
compressed because CPUs are a lot faster now.

It is possible to use lossless data compression on images (or even on
executables). You get back the identical binary image.

At the simplest level the previous line of the image is quite a good
predictor of the next one. PNG and some other formats exploit this
adjacent pixel image data redundancy and then do lossless compression
LZH or similar on the residuals.

Regards,
Martin Brown
 
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Kennedy McEwen
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      04-02-2009
In article <gr2obo$cuo$(E-Mail Removed)>, John McWilliams
<(E-Mail Removed)> writes
>David J Taylor wrote:
>> John McWilliams wrote:
>>> dan c. wrote:
>>>> On Apr 1, 8:28 am, Kennedy McEwen <(E-Mail Removed)> wrote:
>>>
>>>>> Firstly, if you save both images uncompressed then the 200 ISO and
>>>>> the 3200 ISO files will be exactly the same size. Ie. it is the
>>>>> compression that is generating the size difference.
>>>
>>> This part is incorrect. Higher ISOs will have more noise, other things
>>> being equal.

>> How will having more noise affect the size on an uncompressed image?
>> Agreed that, when compressed, a noisier image may have a larger file
>>size.

>
>My RAW files, as they come from the camera, are of different sizes, not
>by much, but a few percentage points up or down. Are you saying camera
>compression of the RAW data causes this?
>

Yes - compression can be lossless.
--
Kennedy
Yes, Socrates himself is particularly missed;
A lovely little thinker, but a bugger when he's ****ed.
Python Philosophers (replace 'nospam' with 'kennedym' when replying)
 
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Kennedy McEwen
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      04-02-2009
In article <(E-Mail Removed)>, Alan Browne
<(E-Mail Removed)> writes
>Kennedy McEwen wrote:
>
>> There is just as much crap in that assessment as there is in the very
>>claims that you dispute in your first sentence.

>
>Part of what Rich says is true although nothing to do with his (as
>usual) idiotic presentation.
>
>Film has so much dynamic range and no more. But high end scanners scan
>beyond that and store beyond that. The part that is noise or simply
>out of dynamic range is just filler bits in the resulting uncompressed
>file.
>
>Many scanners are 16 bit/colour yet there is arguably no more than 13 -
>14 bits of dynamic range in the film. So 2 - 3 (up to 18%) bits of the
>scan data is indeed garbage/filler. Because of bit, byte, word
>ordering and the setting of those garbage bits by the scan s/w they
>might not be compressed out if they are not constant.
>

The mistake here is that you are talking about dynamic range of the
film, not of the resulting image. Some film, eg. Kodachrome, has a
dynamic range which can easily exceed 16 linear bits. The emulsion
itself does not have that dynamic range in sensitivity, but the
resulting image has. On the other hand, some film has the 12-13
equivalent bits of sensitivity compressed into a dynamic range of only
around 8-bits (eg. most C-41 negatives).

>Where the film itself does not resolve to the ability of the scanner is
>further waste as well. Where a 4000 - 6000 dpi scan of high res film
>does yield mainly useful information, that is not so of most ISO 100
>and higher films.
>

However, films like Provia can and do exceed the resolution of 4000ppi
scanners, especially with high contrast images.
--
Kennedy
Yes, Socrates himself is particularly missed;
A lovely little thinker, but a bugger when he's ****ed.
Python Philosophers (replace 'nospam' with 'kennedym' when replying)
 
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