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Could you actually see photos made from RAW files?



 
 
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  #21  
Old June 1st 09, 08:10 PM posted to rec.photo.digital,uk.rec.photo.misc
nospam
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Posts: 24,165
Default Could you actually see photos made from RAW files?

In article , Bob Larter
wrote:

TTBOMK, the only transformation is the A2D
conversion. And that lack of transformations is, after all, the whole
point of the RAW file format in the first place.


basically that's true, however, nikon did apply white balance to the
raw data in some cameras before writing it to the file (d1 series, if i
recall). i doubt that's what he meant, and as far as i know, it's no
longer done.


God, I'd hope not! There are two reasons why I shoot RAW: (1) to get the
most dynamic range from my shots, ie; to push them a stop or two, & (2)
To fix the white balance for shots that were taken under mixed lighting.


turns out it was the d2x.

http://imaging.nikon.com/products/im...ne/10/index_02.
htm

Conventionally, white balance is conditioned digitally. Once an image
is taken with a digital camera, A/D conversion occurs first, then
this digital image is evaluated to determine the white balance value,
according to the conventional process. With the D2X, however, the
white balance adjustment is in analog, which means that white balance
value is determined for the image before A/D conversion. So we had to
figure out a new mechanism for this.

i don't think it's inherently bad, especially if it does produce better
results, but i do agree that raw should be raw.

not to sidetrack, but the only cameras that actually do a transform are
sigma/foveon. the raw data in a sigma raw file is *not* what came off
the sensor and has gone through quite a bit of processing before being
written to the file (which is kinda funny, given the crazy claims about
it being 'true colour').


Yuck. IMHO, the whole point of RAW images is that they haven't been
screwed around with.


the cameras have a 12 bit a/d converter so the raw values should be
0-4095. instead, they range from negative numbers to around 10,000. i
don't know why they did that, since the original sd9/10 only outputted
raw and you *had* to process it (again) on the computer.

what's ironic is the sigma fanbois brag about true colour, the purity
of the data, how nothing is interpolated and how perfect the results
are. it turns out there's actually *more* going on than with bayer.
  #22  
Old June 1st 09, 10:54 PM posted to rec.photo.digital,uk.rec.photo.misc
Eric Stevens
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Posts: 13,611
Default Could you actually see photos made from RAW files?

On Mon, 01 Jun 2009 06:12:17 -0400, nospam
wrote:

In article , Eric Stevens
wrote:

The "RAW data file" is merely a file containing the
camera raw data. The only part of the file that relates
to the image is the data it contains. Which is to say
that we *are* talking about the "RAW data", even if you
want to call if a "RAW data file". It's the same data
either way.


Nope. What comes out of the sensor is not what is saved in the RAW
file. There is a transformation involved.


what type of transformation and from what to what?


There is no single answer. It depends on the camera and the
manufacturer. I suppose there are cameras which save a RAW file which
is nothing but a bit-map of the sensor but generally the RAW file is
modified in some way. In the case of the Nikon D300 there are several
choices as to how the RAW file may be saved:

Compressed, lossless compression or lossy compression.

12 bit or 14 bit.

I don't know the details of this but I expect that some of it is
described in the Nikon Software Developers Kit. Whatever it is that
happens, clearly there is a transformation of some kind. It is
interesting that the D300 manual specifically says of the lossy
compression:

"NEF images are compressed using a non-reversible algorithm,
reducing the file size by about 40-55% with almost no effect on
image quality"

This contradicts what I was saying to Floyd: it is not possible to go
back to the original sensor image from the RAW file. There will be a
range of slightly different sensor images which could produce the same
RAW file.

depending on the camera, there may be minor changes such as analog
white balance or noise reduction, but for all intents the data in the
raw file *is* the data off the sensor, at least with bayer sensors.

Note that "sensor data", in the context of this
discussion, would be the analog data directly read from
the sensor ....


... what analog data?


from the sensor, before the a/d converter.

Second, in the case of the Nikon
D300 the update has changed the way in which the raw data from the
sensors have been interpreted and saved to the RAW file.

Nice try, but I just read the release notes for Nikon's
upgraded firmware for the D300, and saw exactly *nothing*
like what you are saying.

Provide details, and be specific.

What do you make of:

. Image quality: NEF (RAW ) + JPEG
. NEF (RAW) recording: Lossless compressed or Compressed
. Image size: S or M

That sounds like a change in the way raw data from the sensors have
been interpreted and saved to the RAW file.


no it doesn't. the first is embedding the jpeg in addition to the raw
data and the second is how it's compressed. the third is for the size
of the jpeg file. raw files are always full size, with canon's sraw
being an exception (and since this is a nikon d300, not applicable).


See above. The RAW data can be compressed independently of the JPEG
compression.

I wouldn't argue with you over what you have just said but I would
like to point out that this discussion has been about the interpolated
data saved in the RAW file.

The raw data saved in the RAW file is not interpolated.

See the last line of ...
http://en.wikipedia.org/wiki/Bayer_filter

"Bryce Bayer's patent called the green photosensors
luminance-sensitive elements and the red and blue ones
chrominance-sensitive elements. He used twice as many
green elements as red or blue to mimic the human eye's
greater resolving power with green light. These elements
are referred to as sensor elements, sensels, pixel sensors,
or simply pixels; sample values sensed by them, after
interpolation, become image pixels."

Didn't you read what that paragraph says????

Are you unable to determine that the "after
interpolation" is refering not to generation of data
that goes into the RAW file, but rather what is done
with data *from* the RAW file in order to make an image
(such as TIFF or JPEG). That is what "image pixels" means.


Haw! You really don't understand what Bayer interpolation is all
about.


if anyone doesn't understand it, it's you. nowhere in what *you*
quoted says the data in the raw *file* is interpolated.


I've got to plead guilty to that. In a moment of brain fade I got
sucked into what Floyd was trying to talk about rather than the
original topic which I was trying to talk about. Rereading all this
below I can see that I had become more than somewhat confused.

the interpolation is done in the raw converter on the computer, long
after the raw file has been created.

The data saved in the RAW file has not yet been
interpolated, ....


How else do you reckon it is derived from the Bayer mosaic?


the data in the raw file is *before* the interpolation is done to
demosaic the image.

... and when it is interpolated it is *not*
saved in the RAW file, and is no longer considered "raw"
data.


Well, at least you understand that much.


odd, because that contradicts what you've been saying.

However, in addition to that
the JPEG image which results from interpolation simply
does not contain anything like the full amount of
information that was in the RAW file's data. You cannot
reverse the process.

HOW DO I MAKE IT CLEAR THAT FROM THE BEGINNING WE HAVE BEEN TALKING
ABOUT THE RELATIONSHIP BETWEEN THE ORIGINAL IMAGE ON THE SENSOR AND
THE 'RAW' FILE.

Then don't talk about interpolation and other software processing
of the raw data, all of which takes place on data *after* it is
placed in the RAW file.


Dingbat - interpolation is an assential part of going from the Bayer
array to the RAW data file. Please don't continue to pretend
otherwise.


no need to pretend otherwise since that's totally incorrect.

I've quoted
from the original articls, and you still keep trying to switch to
conversion from RAW to JPG. That's an entirely different question.

Then stop talking about processing the RAW data to make an image.


I haven't been. If anything I've been talking about working backwards
from the RAW data file to reconstruct the original image.


that doesn't make any sense.


I'm talking in the hypothetical sense of being able to derive from the
RAW data the light pattern which fell on the sensor to create the RAW
data in the first place. In the case of RAW data which has not been
messed around in some way there is only the one sensor image which
will correspond.



Eric Stevens
  #23  
Old June 1st 09, 11:24 PM posted to rec.photo.digital,uk.rec.photo.misc
nospam
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Posts: 24,165
Default Could you actually see photos made from RAW files?

In article , Eric Stevens
wrote:

The "RAW data file" is merely a file containing the
camera raw data. The only part of the file that relates
to the image is the data it contains. Which is to say
that we *are* talking about the "RAW data", even if you
want to call if a "RAW data file". It's the same data
either way.

Nope. What comes out of the sensor is not what is saved in the RAW
file. There is a transformation involved.


what type of transformation and from what to what?


There is no single answer.


that's ok, just one example is fine.

It depends on the camera and the
manufacturer. I suppose there are cameras which save a RAW file which
is nothing but a bit-map of the sensor


actually, just about every camera.

but generally the RAW file is
modified in some way.


nothing that would affect bayer interpolation. there may be some noise
reduction or in the case of the nikon d2x, white balance.

In the case of the Nikon D300 there are several
choices as to how the RAW file may be saved:

Compressed, lossless compression or lossy compression.


compression is not modification. it's there to save space. users like
being able to put more photos on a card so smaller raw files is a plus.


now, the lossless compression is a modification, although nikon claims
it's 'visually lossless.' it's also optional and it's a tradeoff for an
even smaller size image.

12 bit or 14 bit.


that's not a modification, that's choosing the resolution of the a/d
converter.

I don't know the details of this but I expect that some of it is
described in the Nikon Software Developers Kit. Whatever it is that
happens, clearly there is a transformation of some kind.


if it's so clear, where's the evidence?

It is
interesting that the D300 manual specifically says of the lossy
compression:

"NEF images are compressed using a non-reversible algorithm,
reducing the file size by about 40-55% with almost no effect on
image quality"

This contradicts what I was saying to Floyd: it is not possible to go
back to the original sensor image from the RAW file. There will be a
range of slightly different sensor images which could produce the same
RAW file.


lossy compressed raw is the only case where you don't have an exact
sensor dump (but it's *very* close). fortunately, the d300 offers
uncompressed and lossless compressed.

That sounds like a change in the way raw data from the sensors have
been interpreted and saved to the RAW file.


no it doesn't. the first is embedding the jpeg in addition to the raw
data and the second is how it's compressed. the third is for the size
of the jpeg file. raw files are always full size, with canon's sraw
being an exception (and since this is a nikon d300, not applicable).


See above. The RAW data can be compressed independently of the JPEG
compression.


yea and?

Haw! You really don't understand what Bayer interpolation is all
about.


if anyone doesn't understand it, it's you. nowhere in what *you*
quoted says the data in the raw *file* is interpolated.


I've got to plead guilty to that. In a moment of brain fade I got
sucked into what Floyd was trying to talk about rather than the
original topic which I was trying to talk about. Rereading all this
below I can see that I had become more than somewhat confused.


at least you realize you're confused.
  #24  
Old June 1st 09, 11:30 PM posted to rec.photo.digital,uk.rec.photo.misc
Eric Stevens
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Posts: 13,611
Default Could you actually see photos made from RAW files?

On Mon, 01 Jun 2009 02:45:35 -0800, (Floyd L.
Davidson) wrote:

Eric Stevens wrote:
On Sun, 31 May 2009 23:44:15 -0800,
(Floyd L.
Davidson) wrote:

Eric Stevens wrote:
You actually are that dense!

I read the words. I even quoted them down below. In fact, because you
have (surreptitiously) snipped an awful lot of what follows, its only
two paragraphs down.

You still think that I should quote your entire silly article.
That is *dense*.


Hell No! You should cut and paste my article to make it mean whatever
you would like it to mean. :-(


I have changed the silly
things you've written, and I changed
the meaning of a single sentence. Please blame
me for what you write!


Do you see what happens when you delete text without indicating the
fact?

Again though, it's time that you learned that proper
Usenet netiquette is to trim the quoted text to only that
require for context. I do that. You don't.


Agian though, its time that you learned that proper Usenet netiquette
is to indicate where you have trimmed the quoted text. I do that. You
don't.

And it isn't at all difficult to determine which that
would be, Eric. Try, for example, to get a grip on
"interpolation" before you continue on with this
discussion. Try learning where software is used in the
data flow, and where it is a purely hardward process.


YOU try looking up interpolation in the context of the Bayer process.
I've done it once already for you. It didn't seem to ring a bell, even
the first time.


Such as where you quoted Wikipedia, and didn't
understand what it said! As noted just 5 or so lines
above, learn something about the data flow.

You made it false by chopping out the text around it which made clear
what I was talking about. For the benefit of others I had written:

"The sensor locations are irrelevant. The RAW data is derived
from the sensors by rules which are determined by the
manufacturer of the camera. The signals generated by the
sensors are determined by the rules inherent in the camera's
software. As I have already said, there is a one to one
correspondence between the source image and the RAW
file. You don't have a choice of RAW files for a given image.
Nor do you have a choice of images for a given RAW file".

Yes, and your statement is still false. Explaining a
false statement doesn't change the fact that it is
false.

False: "sensor locations are irrelevant"

False: "signals generated by the sensors are
determined by ... software"

False: "Nor do you have a choicce of images
for a given RAW file"


Look up Bayer interpolation.


And you'll find: 1) that sensor locations are relevant; 2) that
the signals generated by the sensors are not determined by
software, as that is a purely hardware domain; 3) that
the RAW file is data which has not been interpolated, and
when it is interpolated there are many choices for a given
set of raw data.


I agree about the interpolation. As I explained in another article, I
boobed on that. The question has never been just one of interpolation
or no interpolation. Its been about the transformation of the image
which falls on the sensor to the data which is recorded in the RAW
file. One image gives one set of data. The one set of data can only
give the one sensor image (except for the Nikon RAW files using a
lossy compression).

Note that interpolation is not what generates the data
in a "RAW file", it is what generates a TIFF or JPEG
formatted image file. Remember that you wanted to only
talk about RAW data, not the JPEG... but here you are
once again discussing the processing of data to produce
an image file...

Hmmm... right here it is:

First we are not talking about the RAW data. We (should) always have
been talking about the RAW data file.

The "RAW data file" is merely a file containing the
camera raw data. The only part of the file that relates
to the image is the data it contains. Which is to say
that we *are* talking about the "RAW data", even if you
want to call if a "RAW data file". It's the same data
either way.


Nope. What comes out of the sensor is not what is saved in the RAW
file. There is a transformation involved.


That is a hardware transformation, not one that is
called interpolation and not one that is done with
software.

Note that "sensor data", in the context of this
discussion, would be the analog data directly read from
the sensor ....


... what analog data?


The sensor is an analog device.


Not really. It's counting photons.

...(though in other contexts those words might
be used to mean the digital data too).


I see you have had second thoughts.


Neither of us has used it in that context, and since you
have repeatedly confused various parts of the data flow
it is absolutely essential to differentiate the analog
sensor data from the digital data output of the ADC.

In many contexts the sensor, the ISO amplifiers, and the
ADC are all considered "the sensor" in order to simplify
a discussion that really does not involve them other than
as a unit. This is clearly not one of those discussions.


Thats all part of the firmware which transforms the sensor data in the
data of the RAW file.

"RAW data"
clearly must refer to the digital data that goes into
the "RAW file". That is the only place where "RAW" is
used. (And I often use "raw", simply because "RAW"
is grammatically incorrect. They are the same.)

Second, in the case of the Nikon
D300 the update has changed the way in which the raw data from the
sensors have been interpreted and saved to the RAW file.

Nice try, but I just read the release notes for Nikon's
upgraded firmware for the D300, and saw exactly *nothing*
like what you are saying.

Provide details, and be specific.

What do you make of:

. Image quality: NEF (RAW ) + JPEG
. NEF (RAW) recording: Lossless compressed or Compressed
. Image size: S or M

That sounds like a change in the way raw data from the sensors have
been interpreted and saved to the RAW file.


It looks like the specifications from the User Manual to
me. Where's the change?


I don't know. All I know is that the text above has been cut and
pasted from the Nikon site
http://nikoneurope-en.custhelp.com/a...ail/a_id/25962
describing "D300 Firmware Update 1.10 Windows". Clearly the downloaded
software has something to do with the transformation of the sensor
data to the data of the RAW file.

Granted though that they *could* upgrade the firmware
with a different RAW file data format. I can see how
*you* would call that a change in the data, but in fact
it isn't. It is a change in the way the data is
represented and stored in the file, but the *value* of
the data remains the same. Which is to say that the
data values which a raw converter will use for
interpolation will not be different. That processing
is merely encoding of values, not a form of processing
that affects the data or the images that are eventually
produced.


The original argument was over whether or not it was possible to work
back from the RAW data and arrive at more than one sensor image. I
said that subject to statistical limitations there is only one sensor
image corresponding with the RAW data of the file. This raised the
question of the transformation of the sensor data to the data of the
RAW file. One aspect of the argument is whether there is any
transformation and I say there is. Then we got sidetracked onto
whether or not the transformation is all hardware, and I said that
software may be involved. That's why the question of the firmware
upgrade of the D300 entered the picture. The point of this is that the
RAW file data may not just be dump of the sensor data.

All of this is irrelevant to the original question which was centered
around whether the transformation from sensor image to RAW file data
was fully reversible. In most cases it is in which case you can show
that only the one sensor image corresponds to any one RAW file data
set. I described this as being a 'one to one' relationship. This is
where the current furore started. A moment's brain fade let me be
dragged into questions of interpolation but I was clearly wrong. I'm
going to ignore that issue.

--- snip ----



Eric Stevens
  #25  
Old June 1st 09, 11:39 PM posted to rec.photo.digital,uk.rec.photo.misc
Eric Stevens
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Posts: 13,611
Default Could you actually see photos made from RAW files?

On Tue, 02 Jun 2009 02:59:51 +1000, Bob Larter
wrote:

Eric Stevens wrote:
Nope. What comes out of the sensor is not what is saved in the RAW
file. There is a transformation involved.


What transformation is that? TTBOMK, the only transformation is the A2D
conversion. And that lack of transformations is, after all, the whole
point of the RAW file format in the first place.


AFAIK the contents of the RAW file (ignoring metadata etc) is a fully
detailed map of the sensor data but is not just a 'dump' of the sensor
data. At the very least the quantized sensor voltage has to be
transformed into 12 or 14 bit data. Various corrections may be applied
in the process.



Eric Stevens
  #26  
Old June 1st 09, 11:45 PM posted to rec.photo.digital,uk.rec.photo.misc
Eric Stevens
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Posts: 13,611
Default Could you actually see photos made from RAW files?

On Tue, 02 Jun 2009 00:28:02 +1000, Bob Larter
wrote:

Eric Stevens wrote:
On Sun, 31 May 2009 16:11:00 -0800, (Floyd L.

[...]
I've been talking about the RAW file from the beginning. So too were
you at that time. Remember "Floyd, I suspect you have been smoking
something which is not good for you. Subject to statistical error
limitations, ... The data in the RAW file can't be restructured to
make a different image without changing the data."


This is incorrect. As Floyd has said, the same RAW data can result in an
infinite number of final images. For example, one can process it with a
huge range of WB values, or change the EV correction by plus or minus a
couple of stops, set the black level to anything you like, etc, etc.
None of these changes require changes to the RAW data, merely the
interpretation of it.


Its incorrect, as you (or somebody) chopped out the important part. I
originally wrote:

"Floyd, I suspect you have been smoking something which is not
good for you. Subject to statistical error limitations, there is a
one to one correspondence between the source image and the
RAW file. One can be converted to the other using the rules
inherent in the camera's software. The data in the RAW file can't
be restructured to make a different image without changing the
data."

We were then talking about the "source image" - that which was
projected onto the sensor by the lens - and not that infinite range of
images which could be created downstream by the manipulation of the
RAW data.



Eric Stevens
  #27  
Old June 1st 09, 11:50 PM posted to rec.photo.digital,uk.rec.photo.misc
Eric Stevens
external usenet poster
 
Posts: 13,611
Default Could you actually see photos made from RAW files?

On Tue, 02 Jun 2009 00:19:18 +1000, Bob Larter
wrote:

Eric Stevens wrote:
On Sat, 30 May 2009 21:32:27 -0800, (Floyd L.
Davidson) wrote:

Floyd has failed to point out that at this point he has omitted a
great deal of previous text. I know he has been around more than long
enough to know that this is not the right thing to do.

Eric Stevens wrote:
Floyd, I suspect you have been smoking something which is not good for
you. Subject to statistical error limitations, there is a one to one
correspondence between the source image and the RAW file. One can be
converted to the other using the rules inherent in the camera's
software.
What do you mean by "the source image"?


That which is projected onto the sensor by the lens.


That's what's encoded in the RAW file. It's a losslessly compressed dump
of the contents of the image sensor, without any interpretation.


Not so. The sensor stores volts. The RAW file maps this in 12 or 14
bit patterns. Some transformation has clearly taken place. Nor is it
necessarily compressed and, if compression has taken place it need not
be lossless.
[...]

file. You don't have a choice of RAW files for a given image. Nor do
you have a choice of images for a given RAW file.
Did you read, and understand, the following few paragraphs?

A JPEG or TIFF file contains an image. The RAW file
contains data to make an image.

For example, each "sensal" location on the sensor does
*not* translate to a single pixel in the resulting
image. Instead the data from at least 9 different
sensors locations is used to determine the Red, Green,
and Blue values for a single pixel.


He's talking about the *process* of converting from the RAW image to the
RGB image that you see on your screen, which includes Bayer
deconvolution. As he says, there is no 1:1 relationship between a pixel
("sensel") on the image sensor & a pixel on the RGB image that you see
on your screen.


My original proposition was that there is a one to one correspondence
between the source image (that which is projected onto the sensor by
the lens) and data which is stored in the RAW file. Its not possible
that any single RAW file could be produced by more than one sensor
image.



Eric Stevens
  #28  
Old June 2nd 09, 01:00 AM posted to rec.photo.digital,uk.rec.photo.misc
Eric Stevens
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Posts: 13,611
Default Could you actually see photos made from RAW files?

On Mon, 01 Jun 2009 18:24:28 -0400, nospam
wrote:

In article , Eric Stevens
wrote:

The "RAW data file" is merely a file containing the
camera raw data. The only part of the file that relates
to the image is the data it contains. Which is to say
that we *are* talking about the "RAW data", even if you
want to call if a "RAW data file". It's the same data
either way.

Nope. What comes out of the sensor is not what is saved in the RAW
file. There is a transformation involved.

what type of transformation and from what to what?


There is no single answer.


that's ok, just one example is fine.

It depends on the camera and the
manufacturer. I suppose there are cameras which save a RAW file which
is nothing but a bit-map of the sensor


actually, just about every camera.

but generally the RAW file is
modified in some way.


nothing that would affect bayer interpolation. there may be some noise
reduction or in the case of the nikon d2x, white balance.

In the case of the Nikon D300 there are several
choices as to how the RAW file may be saved:

Compressed, lossless compression or lossy compression.


compression is not modification. it's there to save space. users like
being able to put more photos on a card so smaller raw files is a plus.


now, the lossless compression is a modification, although nikon claims
it's 'visually lossless.' it's also optional and it's a tradeoff for an
even smaller size image.

12 bit or 14 bit.


that's not a modification, that's choosing the resolution of the a/d
converter.

I don't know the details of this but I expect that some of it is
described in the Nikon Software Developers Kit. Whatever it is that
happens, clearly there is a transformation of some kind.


if it's so clear, where's the evidence?


With all these changes to its form, the original data has clearly been
transformed. This does not mean that its meaning has been changed.
Merely that its form has been changed.

It is
interesting that the D300 manual specifically says of the lossy
compression:

"NEF images are compressed using a non-reversible algorithm,
reducing the file size by about 40-55% with almost no effect on
image quality"

This contradicts what I was saying to Floyd: it is not possible to go
back to the original sensor image from the RAW file. There will be a
range of slightly different sensor images which could produce the same
RAW file.


lossy compressed raw is the only case where you don't have an exact
sensor dump (but it's *very* close). fortunately, the d300 offers
uncompressed and lossless compressed.

That sounds like a change in the way raw data from the sensors have
been interpreted and saved to the RAW file.

no it doesn't. the first is embedding the jpeg in addition to the raw
data and the second is how it's compressed. the third is for the size
of the jpeg file. raw files are always full size, with canon's sraw
being an exception (and since this is a nikon d300, not applicable).


See above. The RAW data can be compressed independently of the JPEG
compression.


yea and?

Haw! You really don't understand what Bayer interpolation is all
about.

if anyone doesn't understand it, it's you. nowhere in what *you*
quoted says the data in the raw *file* is interpolated.


I've got to plead guilty to that. In a moment of brain fade I got
sucked into what Floyd was trying to talk about rather than the
original topic which I was trying to talk about. Rereading all this
below I can see that I had become more than somewhat confused.


at least you realize you're confused.


Your turn now. Have a look at what I am trying to say about the
meaning of transformation. 1/4 = 0.25



Eric Stevens
  #29  
Old June 2nd 09, 02:30 AM posted to rec.photo.digital,uk.rec.photo.misc
Floyd L. Davidson
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Posts: 5,138
Default Could you actually see photos made from RAW files?

nospam wrote:
In article , Bob Larter
wrote:

He's talking about the *process* of converting from the RAW image to the
RGB image that you see on your screen, which includes Bayer
deconvolution. As he says, there is no 1:1 relationship between a pixel
("sensel") on the image sensor & a pixel on the RGB image that you see
on your screen.


there is a 1:1 mapping of senselsixels, although multiple sensels are
used to calculate one pixel. in other words, 10 million sensels on the
sensor- 10 million pixels in the image.


Untrue. There are necessarily more sensor locations
than pixels in the resulting image.

Various different raw converters, all using the same raw
data, produce images of different pixel counts.

--
Floyd L. Davidson http://www.apaflo.com/floyd_davidson
Ukpeagvik (Barrow, Alaska)
  #30  
Old June 2nd 09, 02:43 AM posted to rec.photo.digital,uk.rec.photo.misc
Floyd L. Davidson
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Posts: 5,138
Default Could you actually see photos made from RAW files?

nospam wrote:
In article , Bob Larter
wrote:

He's talking about the *process* of converting from the RAW image to the
RGB image that you see on your screen, which includes Bayer
deconvolution. As he says, there is no 1:1 relationship between a pixel
("sensel") on the image sensor & a pixel on the RGB image that you see
on your screen.

there is a 1:1 mapping of senselsixels, although multiple sensels are
used to calculate one pixel. in other words, 10 million sensels on the
sensor- 10 million pixels in the image.


That's the default, but there's no mathematical necessity for the number
of output pixels to equal the number of output pixels.


i would hope the number of output pixels equals the number of output
pixels

unless you upscale or downscale, the number of input sensels will be
the same as the number of output pixels.


That is not true.

The Nikon D3, as one example, is specified as having a
12.87 Mega pixel sensor. The images it generates are
specified to be 4256x2832, which works out to 12.05 Mega
pixels. Dave Coffin's dcraw program generates a
4284x2844 (12.18Mp) image.

Note also that the camera can generate an image of
2128x1416, and while I do not know the details of how
Nikon implemented that, it is entirely possible (and
very likely) that it is not done by scaling the larger
image to a smaller one, but by simply using a larger
block for interpolation of the raw data.

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




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