Re: Dispute with model over Trade for Copies photo shoot

Pete <available.on.request@xxxxxxxxxxxxxxx> wrote:
On 2010-09-15 17:11:13 +0100, Floyd L. Davidson said:

Pete <available.on.request@xxxxxxxxxxxxxxx> wrote:
<...>
Ok, nothing "views" JPEG, GIF, TIFF, or PNG data
either. They all have to be converted into an image, resized to fit the
display, and colour managed. A "viewer" combines these separate things.
Not true. JPEG, GIF, TIFF and PNG are all *image
formats*. The data
defines a single image. To the degree that it is accurately displayed,
all displays will be the same (which does not mean that all displays are
the same, just that what they attempt to display is the same).
If you want to *change* the image, that data has to be
changed.
Compare that to a RAW data file, which is not an image
and from which an infinite number of *different* images
can properly be produced. The data set is not changed
to produce different images, because there are an
infinite number of *correct* ways to interpolate the
image data from the exact same sensor data.

I don't wish to be argumentative and I realize that "correctness"
depends on whether one's perspective of a subject is microscopic or
macroscopic, detail or essence, beginner or master. I learn a lot from
your posts and I find the quickest way to learn is by presenting my
opinions, having them challenged, and being prepared to change them.
With that in mind, here are my thoughts.

As you know, a NEF file is not just a wrapper for RAW data. It is
Nikon's proprietary *image file format*.

The raw data in an NEF file is not an image. There are
two JPEG images contained within an NEF file, and one of
those actually contains another, very small, JPEG.
Hence I guess you can call it an image file format if
you like, but it really is not. It's actually a
modified TIFF file format... and it's worth noting that
TIFF is a specification for a file format, as well as
for an image format (two distictly different
specifications).

A NEF file fully specifies the one and only image that the file
*currently* represents.

The raw data does not represent any one single image.
It's sensor data, and can *correctly* be interpolated to
any one of an infinite number of images.

As long as you continue to refuse to accept that simple
*fact* (it is a fact, not an opinion) it will be impossible
for you to completely grasp the significance of the process
that generates something like a JPEG image.

It may also contain multiple specifications in
the file metadata, called "versions", to represent a selection of the
almost infinite possible renditions.

Those "versions" of the metadata are not sufficient to
define a specific image (except when used with a
specific raw converter). There are any number of other
variations in how the raw data can be interpolated (and
they are all "correct" too).

For example, those specific options can be applied to
something like /dcraw/, and the results will *not* be
the same image that ViewNX generates.

Notwithstanding, there is only one
*current* version therefore there is only one currently valid image of
the RAW data it contains.

But as noted above they do not entirely specify a single
image.

The underlying principle of data+metadata =
image is the same for all image file formats and this principle is what
enables file "viewers" to be made.

There are multiple methods for interpolating the raw
data. There is no one specific defined image that
results from the data.

Making a format proprietary always has pros and cons as do both the
cast-in-stone and the ever-changing formats/standards. HTTP and XML
being wonderful examples of the latter.

What's that got to do with our discussion though? :-)

ViewNX is a NEF, TIFF, and JPEG file viewer plus basic editor.
It does not "view" or "edit" an NEF file's sensor data.

I've never implied that it does. I fully understand that with most
image file formats the only changes that can be made via metadata are
things such as colour-space and rendition size.

It does not edit the sensor date.

ViewNX and Capture edit the specification for the rendering steps
necessary to create the image from the contained RAW data. The
specification is stored in the metadata. When a NEF file is saved the
specification that is responsible for rendering the currently displayed
image is written into the version named "Last Saved". The camera wrote
its specification into the version named "Original", which cannot be
edited thereby giving NEF the capacity for non-destructive editing.

That does not change the fact that the raw data, even
with the metadata, is not sufficient to specify a
specific image. The same metadata used with a different
interpolation can generate an equally "correct", but
very different image.

When NEF metadata has been edited, ViewNX will display one of two
possible icons in thumbnail view: one indicates that "Quick
Adjustments" have been applied and can be changed by either ViewNX or
Capture, the other indicates that only Capture can make further
adjustments.

Which again is interesting perhaps, but not pertinent.

If you "view" an NEF file it is the embedded JPEG image
that is viewed. While Nikon says it is to "edit" NEF
files, they also specifically say that by "edit" they
mean it converts the RAW data to an image format (JPEG
or TIFF).

Obviously, it must contain the required RAW and other converters. The
small JPEG embedded in the NEF is used only to produce the thumbnail
view.
The "small JPEG" is a full sized JPEG. It is commonly
used to "view" an NEF file. And yes sometimes that is
also done by actually interpolating the RAW data too,
but not usually because that is slow by comparison, hence
it is generally only done when the expectation is that
the data will also be manipulated as it is converted to
an image format such as JPEG.

We are both right and both wrong, Nikon is the odd one out by being
only wrong :-)

I don't see where you've demonstrated that I'm wrong or
that Nikon is wrong. You aren't "wrong", you just don't
quite have a complete grasp of the process by which raw
sensor data is manipulated to generate an image.

You are usually correct so I've been investigating further. It seems
that the camera embeds two JPEGs in EXIF fields: the small one is for
thumbnail view, the large (low quality) one is for a file "viewer", the
default viewing mode for ViewNX. The low quality is to conserve camera
buffer and file space. The camera also uses these JPEGs for its
playback functions. Obviously, it would be pointless for the camera to
save a high quality JPEG in the NEF; it would make more sense to always
save NEF+JPEG and not embed an image in the NEF.

ViewNX displays the rather poor quality large JPEG. If its "RAW" button
is activated the button is animated while the RAW conversion is being
performed. The image is then displayed and cached. Next time the same
NEF is viewed it will use the cached image and not the embedded JPEG,
irrespective of whether or not the "RAW" button is activated. It does
not update the JPEG embedded in the NEF (it would be useful if it did).

Interestingly, when a NEF has been edited by Capture the "RAW" button
is disabled, suggesting that ViewNX then uses only the embedded JPEG.
The NEF file is noticeably larger after the first time Capture saves
it, indicating that it embeds a high quality JPEG. What I've read seems
to confirm this and others have found that Capture removes the small
embedded thumbnail JPEG. The latter point is nothing more than mildly
interesting; I can't be bothered to get and use some EXIF exploration
software, and it is certainly not worth a debate.

Well, if you don't have the tools to work with these
files you probably shouldn't argue about what they are
and how they work...

Apple's Quick Look and Preview display a large image, but it is always
the original version not the current version, which is both pointless
and incorrect. I find it hard to believe that the NEF now stores two
large JPEGs; perhaps it does. When requesting Preview to display a NEF
at 100% there is a considerable delay before the full resolution image
appears, which is not the case for a same-sized JPEG. I've no idea what
is going on and I hope Apple will eventually correct this behaviour.

There are actually three JPEG images, but one is a
comment embedded in one of the others. I can't recall
right now what the size is, but it is very small. It's
used by the camera for small thumbnails when multiple
images are displayed on the LCD.

I'm not really sure which of the other two is used for a
normal preview on the screen, but I suspect it is the
full sized image. That allows it to be magnified, for
example.

Summary of the large JPEG stored in the NEF: it is only a likeness of
the real image. Good enough for a file viewer? Probably.

Only a "likeness"??? It is one of the infinite number
of absolutely correct variations that can be produced
from the raw data.

Thanks for your posts, Floyd. It took me a while to understand the
meaning of an original digital image, but I'm very glad that I got
there in the end. I'll put it to good use when I create more than one
version in a NEF file. My photography will probably never be good
enough to need a traceable method for version control, but I'll make it
a habit just in case.

Yep, that's true of a great deal of relatively "useless"
information. It doesn't result in any big change, but
over the long run it does help.

--
Floyd L. Davidson <http://www.apaflo.com/floyd_davidson>
Ukpeagvik (Barrow, Alaska) floyd@xxxxxxxxxx
.

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