As Agent Gibbs has a habit of saying "English please" to Abbs and Tim the
Geek, what would be the bottom line consequence of having an 11 x 14, a 16 x
20, or a way bigger print made from an 8 bit file as compared to that from
a 16 bit file?
Back in the late 1960s I saw a huge .......... better than 72"' on the long
side ............ black and white print made from a 35mm negative out of an
M3 that look pretty damm good. In something of the same vein what would be
the visual comparison between making that same print from an 8 bit or a 16
bit file?
This curious mind , and maybe those of others, want to know :-)
jh
----- Original Message -----
From: "Moose" <olymoose@xxxxxxxxx>
To: <olympus@xxxxxxxxxx>
Sent: Saturday, October 04, 2008 4:49 PM
Subject: [OM] Re: 16 bit tiff
> John Hermanson wrote:
>> I had been using Raw Shooter Essentials for a while but am now trying out
>> Raw Therapee. Is there any benefit to saving a processed ORF as a 16 bit
>> tiff instead of 8 bit? I don't see it, but 16 bit is twice the file
>> size, 47 meg versus 23.5.
>>
>>
> The sensor is an analog device, as are the first part of the sensor
> electronics.
>
> The analog to digital converter divides up the analog voltages into
> discrete digital steps.
>
> Most DSLRs use 12 bit A/D converters. some high end ones, including the
> E-1 and, I assume, E-3, are 14 bit. Extending dynamic range, as some
> newer sensor stems are now doing, requires more bits if midrange tonal
> detail is not to be compromised.
>
> That translates to 4096 separate brightness step for each color at 12
> bits and 16384 for 14 bit.
>
> If you convert that to an 8 bit TIFF, the luminance range is downsampled
> to 256 steps, throwing away much of the image data you bought the camera
> for. 16 bit's 65536 step range can accommodate all that comes out of
> the camera, without loss.
>
> If an image is simply to be converted and viewed as a JPEG (compressed 8
> bit) or printed on an 8 bit printer, 8 bit files are fine.
>
> As soon as one starts manipulating the file, even with simple tools like
> Levels, Contrast, etc. the software needs to move values around in the
> histogram. With only 256 levels to work with, that can lead to uneven
> stepping effects, even to holes in the histogram (yup, I've seen 'em),
> where working in 16 bit gives the algorithms plenty of steps for subtle
> interpolation.
>
> In practice, some images seem to come through considerable manipulation
> in 8 bit just fine, while others start to look "funny" in ways that I
> find hard to describe. Even starting with an 8 bit image, as in images
> from digicams with 8 bit JPEG output only or those downloaded from the
> web, conversion to 16 bit before processing can make a difference.
>
> How do I know? I "always" convert 8 to 16 bit in PS as a first step in
> editing images from my F30 or Moosterizing images from others. Except
> sometimes I forget that first step - and start wondering why things
> aren't working quite as I expect. A quick glance at the header leads to
> a "DOH" moment and starting over.
>
> Why not 12 and 14 bit versions of TIFF? While certainly possible, such
> files would be messier to process. Going from 8 to 16 bit simply uses
> two bytes per color per pixel instead of one, whereas intermediate
> numbers of bits would require splitting bytes between channels and/or
> pixels. Given the way most programming languages/systems and file
> systems work, that requires custom programming. Back in the dark ages, I
> encoded and decoded 8 different yes/no bits of data into single bytes
> for storage. With the low and dropping cost of storage, I don't see
> anybody going to that kind of trouble today.
>
> There is another reason to use 16 bits to work on 12-14 bit source data
> relating to the limited number of digital steps available to the lower
> values from a linearly converted analog image, but I don't have the time
> or brain power just now to try to explicate it. I seem to recall that
> there's a good explanation on Luminous-Landscape.
>
> Bottom line - 8 bit throws away data you may or may not want later. If
> you don't care, no problem. If you plan to retain the original ORFs and
> software to convert them again later, if needed, that will work short
> term. Long term, storage in a universal format like TIFF is a better
> solution.
>
> Moose
>
> Moose
>
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