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[filmscanners] Re: Compression

It is very interesting how these two threads, this one regarding the
digital/film comparisons regarding the newest Canon digital camera, and
the other thread regarding "over resolving scans" have independently
come to the same issues, those of aliasing and grain.

I hope people who have been reading one, are also reading the other,
since these discussion is expanded by the content of the responses to
both threads.

I'm not sure you are suddenly retired.  I think it more that you are
being called up to consult.  Here in N.A. consulting is the "new"
moneymaking manner to label oneself.  You aren't "retired", you are
brought out to consult.  Along with the title comes $1200 a day fees or
more.  When you find your pockets filled, you go back into "research"
and disappear for a while, until you need a new car or boat or house,
and then you become available to consult again. ;-)


Tony Sleep wrote:

> On Thu, 10 Oct 2002 20:11:05 -0500   (snsok@swbell.net) wrote:
>>Can you elaborate on your reservations about his film to digital
>>Certainly the images he presents on the first page are compelling.
> ============
> Posted: Oct. 07 2002,06:02
> http://www.luminous-landscape.com/cgi-bin/forum/ikonboard.cgi?s=22bbee94446
> c12b81694a1f3749970c5;act=ST;f=4;t=15;st=60
> A couple of points which hopefully add a little on aliasing/tonal
> smoothness, and dynamic range. My biggest concern with the review and
> conclusions is how the #### I am ever going to afford a 1DS...
> [Quote]
> Of course there will now be a chorus of those who say, "Ya, but a drum scan
> would have really shown a bigger
> difference in favour of film." Humm. Maybe. But here are my thoughts on
> this recurring topic. I have had drum scans made from my 35mm and medium
> format film on several occasions. Yes, an 8000 ppi scan is impressive, and
> can make bigger prints. But, I'm also convinced that while they give me
> more pixels, I don't get a whole lot more real data. There simply isn't
> that much more information on film than about 4,000 PPI. Above that we get
> bigger files, but not much more information. Maybe, 20% more than the 3200
> PPI scans that my Imacon Flextight Photo scanner is capable of, but not 2
> or 3 times as some inexperienced people presume from the numbers.
> [/Quote]
> I agree with Michael's 4,000ppi  'diminishing returns' assessment as far as
> image detail is concerned, but it isn't enough to reach conclusions
> regarding tonal smoothness.
> Film grain is irregular both in size, distribution and topology, and all of
> these attributes interact with the fixed geometry of pixel size and
> distribution. What many people believe is grain in their scanned images is
> often aliasing, which produces an exaggerated grain-like structure
> comprising false colour/false luminance pixels.
> Avoiding this in low-pixel-count scanners is only possible by using a
> low-pass optical system (soft lens or antialiasing filter) which hurts
> image detail as well.
> Grain aliasing can be so extreme as to render a scan unusable, especially
> with grainy, fast B&W silver-based films, but generally it is acceptable
> with scanners  >=4,000ppi.
> When it happens, the result is far more 'texture' than the film image
> exhibits when viewed or printed by analogue techniques.
> Having seen comparative drum scans of an ISO100 tranny done at 4,000,
> 8,000, and 12,000 ppi, there isn't much gain in resolution of image detail
> above 4,000ppi, which accords with what Michael says in his review. By
> 8,000 ppi the scan has virtually all of it. Yet 12,000ppi shows a
> significant increase in grain detail over 8,000ppi, with better rendition
> of individual grain shapes. A lot of people say this doesn't matter, grain
> detail is not image information we want...
> However, if we don't capture precise grain information, what we get through
> the conversion to pixels is aliasing, and a characteristically false and
> 'noisy' rendition of the film image. An Imacon scan at 3,200ppi necessarily
> adds an unknown  extra dimension of aliasing noise.
> How much, and how destructive depends on the anti-aliasing filter and CCD
> properties, even the lightsource, but it is important to recognise that any
> comparison with scanned film is not a comparison with film itself.
> Pedantically, I think it would be worth doing a comparison involving a
> 12,000ppi drum scan, to get a more absolute measure of the differences
> between the film images and the EOS1DS. Not for the sake of resolution per
> sebut to judge relative tonal smoothness more accurately.
> Having said all that, I am sure digital will still win, but the existing
> methodology probably makes film look rather worse than it is in this
> respect (and JPEG'ing of an image full of aliasing products compounds the
> issue, to film's disadvantage).
> Michael's observation of moire and the artefacting of the red-shed boarding
> are more of the same. Aliasing is inherent with pixel-based systems, though
> the Foveon sensor will avoid  colour aliasing and only alias luminance.
> For me, the only obvious remaining advantage of film (apart from avoiding
> divorce and bankruptcy) is dynamic range.
> My main interest and use of scanning is so I can use colour negative and
> B&W chromagenic films, exactly because they have a mad dynamic range : what
> you can see with adaptive eyes, you can photograph, pretty much.
> I have tested and found 12+ stops with these materials. 10 stops of this is
> completely usable, there is severe compression in the rest, but it is still
> there. This is absolutely liberating compared to tranny, and gives me the
> control I only had in the wet darkroom with B&W, and more.
> Alongside this, the D1S is, as reported, distinctly poor at 6 stops.
> What's more, it is almost certainly an engineered inhibition. CCD sensors
> can now achieve 14 stops range, and do so completely linearly. I don't know
> any reason why CMOS should be worse, so it sounds like Canon have knobbled
> the range.
> I hope this will prove to be something that applies only to JPEGS, and the
> RAW files will contain far more range.
> There is a very good reason why Canon may have done so : wide range images
> look absolutely awful on-screen, impossibly flat, low contrast. You have to
> work with them, as raw material, and you wouldn't want to have to cope with
> the consequences of JPEG, it has to be clean, raw, high-bit data.
> So the JPEG format is probably assumed to be for rapid onward transmission
> as a production file, with levels set, and only 8bit/ch available. To do
> anything else would frighten the desk editor who receives the file, and
> involve them in making judgements which are best left to photographers...
> Fingers crossed, anyhow.
> Regards
> Tony Sleep (sometime filmscanner reviewer - suddenly retired
> ============

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