Cory Papenfuss wrote:
I would be surprised if in-camera produced TIFFs are 16 bits. They
would be extra-huge if they were. Pentax's RAW files basically
*are* TIFFs (zero padded 12->16 for the -D, and packed 12->12 for
the -DS). The difference is that only a single plane of 6megapixel,
12-bit data is necessary in RAW, but an interpolated version for R,
G, and B is needed for TIFF.
I started wondering now if you might actually store the "raw"
representation in a TIFF file, since different colour models (not
just RGB) are supported, but perhaps not quite. You can save data as
luminance/crominance, but I guess that's not exactly the same thing.
And only RGB images would be considered baseline TIFF, I think.
All a TIFF file is is a standardized format for storing bitmapped
images, as well as whatever tags you like. The thing with RAW is that
it's not a color model, it's a monochrome image. It's understood that
the monochrome image should be interpretted according to a RGBG Bayer
pattern.
I think you can argue that this does indeed make it a colour model, or
rather - the data is just data of course, the "RGBG Bayer pattern"
interpretation would be the colour model. The actual data in a normal
RGB TIFF file is after all also indistinguishable from monochrome image
data...
Only after that is done (and there are many ways to do it) can you
have a three-color-plane image. Pentax likely chose TIFF as the
baseline for their RAW format because it's an extensible, existing
format. It doesn't need much tweaking (12 vs. 16 bits for one).
Probably...
I've also been thinking that they should not really call it RAW, by the
way. A "raw" image file is traditionally a file containing the pixel
data and nothing else.
Yes. I suspect that the difference would be a lot smaller with
(lossless) compression, though...
Somewhat smaller, but not much I wouldn't think. The standard
TIFF supports only a few types of compression, most of which aren't
all that great. It's similar to taking a document, copying it three
times, making small changes in each one, and then compressing the
three. Chances are it's going to be a fair bit bigger than the
original compressed.
I must admit I haven't tried this, but isn't some of the "extra" data
introduced by interpolation duplicate date that might easily be reduced
in size by traditional compression algorithms.
Large tiffs may be an acceptable compromise. It's much bigger
than it needs to be, however, and does lose a slight bit of
flexibility.... not nearly so much as 8-bit gamma tiff or JPEG, though.
My point exactly. While the referenced text suggests that TIFF has no
advantages over JPEG...
The way it's typically done in-camera (8-bit, white-balanced,
gamma-corrected), it does have almost no advantages over minimally
compressed JPEGs, and the disadvantage of being much larger...
It has the advantage that you know you have lossless compression. Even
"minimal" JPEG is lossy, isn't it? Unless you use JPEG-2000, which also
allows lossless compression, as far as I understand. And has several
other features making it a generally much more usable image format, but
the article of course dismisses it without any discussion...
usually
larger than the RAW.
-Cory
