Re: [Openexr-devel] OpenEXR vs Raw images

[Richard Annema]

Hi there,

Although you should feel free to use whichever file format you are most
comfortable with, here are a few reasons why you may want to use OpenEXR
rather than specifically the Canon RAW file format.

- Canon RAW file format is not officially documented, let alone that source
code is provided. Indeed, Canon have continually been making changes to this
format such as introducing a TIFF mode for the Canon D1 DSLR. OpenEXR is not
only fully documented, but full source code is available.
- Canon RAW files store data in 10 bits per channel - which is a large part
of the filesize savings you're seeing, regardless of lossless JPEG
compression or not - as opposed to 16 bits per channel (HALF) or even 32
bits per channel (FULL) in OpenEXR.
- Canon RAW files store data as a complex composite coming from the CCD.
OpenEXR, on the other hand, stores data straight-forwardly per channel, per
pixel. (Though note that this only applies to the suggested data formats. At
SplutterFish, for exampled, we've added a PackedIntRGBa data format to add
8bit/channel support.)
- Canon RAW files store only that data which Canon deems necessary. The
OpenEXR format on the other hand is more of a 'container' file formar which
can carry many, many data formats and types including comment fields.
- Canon RAW files, as far as I know, don't store any alpha channel. Though
this will be a moot point for plain photography (not really possible to
photograph transparency), if you were to use images for compositing the lack
of alpha channel capability is a major reason not to use the format at all.
OpenEXR does specify an Alpha channel, and you're free to add any specific
channels yourself. Specifically for 3D applications this could be a
Z-Buffer, for instance.

Although there are many more reasons why you would want to use OpenEXR
instead of Canon RAW, I think it's best to think of it as this: Canon RAW is
very efficient at what it does (kudos to them on that) - but that which it
does is far too restrictive for general purpose use.

I'm not sure if this is the conclusion of your inquiry; "Should I convert my
Canon RAW files over to OpenEXR ?"
But if it is, I would have to say that you should only do so if you need it.
If the Canon RAW file format does everything you want, and you see no
benefit in using OpenEXR, then you should stick with the Canon RAW file
format (though I'd keep an eye on what utilities can decode them, lest you
get stuck with unreadable files at some point in the future).
After all, nobody (I hope) is converting their JPG collection to OpenEXR
either.

As for your comment on tweakability - this is purely software. If using the
full extent of the fileformat, though, I would say that OpenEXR allows for
more fine control than the Canon RAW format does, simply because it offers a
higher dynamic range.

Kindest regards,
Richard Annema
Director of Client Relations
SplutterFish, LLC

----- Original Message ----- 
From: "nkb" <address@hidden>
To: <address@hidden>
Sent: Monday, December 22, 2003 15:19
Subject: [Openexr-devel] OpenEXR vs Raw images


> Hi.
> I've a simple question.
> Does storing my images in OpenEXR present any advantages over storing my
> images as Raw images (such as the CRW format from Canon digtial camera)?
> I did a simple comparision. In terms of file size, for the same image,
> canon crw file size (in my example) is 4.7MB while openexr format with
> piz compression yields a result of 12.8MB. Further, in terms of being
> able to control the exposure levels, tuning the images with various
> details, crw format seems to have more controls and I'm able to get the
> right image out of a CRW file.(I use photoshop CS) So what am I missing
> here? Thanks.
>
>
>
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