voile parasite

Claire Cox (asker) Jul 24, 2013:

Thank you, everyone, for your help here. I went with veiling in the end.

Sheri P Jul 17, 2013:

This ref. calls the min. density the "basic veil" and goes on to list "outside" factors that can lead to what the author simply calls "higher veil values". Maybe relevant?
http://books.google.com/books?id=GSd0IqSt3bsC&pg=PA142&lpg=P...

Claire Cox (asker) Jul 17, 2013:

@Tony Thanks, Tony, for explaining this further - it is much appreciated. Unfortunately this is the first (and so far only) time this voilage has been mentioned. I'm translating a list of specifications for qualification of such examination processes and there really isn't much to go on.

Tony M Jul 17, 2013:

@ Asker In any film system (and others, by analogy) there is a certain minimum density (i.e. the film is not perfectly clear) — in your context, this is included as one of the first-order factors that will limit the inherent detection sensitivity.

But there is also the possibility of this 'veiling', which may arise from a number of different causes (is this explained later in your text?), but which is NOT inherent to the process itself, and hence is excluded from this list of limiting factors.

Claire Cox (asker) Jul 17, 2013:

Well now I'm thoroughly confused! Would any more context help to clarify this matter, because I'm well out of my depth....

Tony M Jul 17, 2013:

@ Chris I believe it's the other way round?

chris collister Jul 17, 2013:

It seems to me that what they are talking about is the minimum optical density excluding the unavoidable/inherent non-zero density offset. Or have I missed something?

Tony M Jul 17, 2013:

@ Chris Yes, absolutely — but that's not quite what the question term is about; the 'voile parasite' is here being specifically excluded from your 'density floor'.

chris collister Jul 17, 2013:

Yes, the minimum optical density for a perfect material is zero, but real photographic film raises the optical floor, as it were, mainly on account of the unexposed emulsion, in which there are always a few halide grains which have become converted to silver. In electronic instrumentation terms this would be described as a "noise floor", so you could describe the optical analogue as an "opacity/density/transmissibility floor".

Tony M Jul 17, 2013:

Veiling In film technology, we do talk about 'veiling' (or sometimes 'fogging') to describe this kind of effect, so I think it would probably apply in this sort of context — the minimum density ought normally to be 100% transparent film, but any 'background' veiling would cause there to be some residual density. I would probably avoid 'fogging', as that tends to lead the reader to imagine the cause of the density, which is probably not relevant here.
And I'd steer clear of 'parasitic', as not really being applicable to this imaging context; the idea here is probably more like 'spurious' (though there may be the same notion of 'interference' behind it as in telecommunications) — though arguably, 'veiling' in EN is inherently unwanted (hence spurious), and do it might not even be necessary to render that at all.

Re-reading, it seems as if the minimum density expected is due to the process as a whole, whereas this spurious effect (not being included here as an influencing parameter) presumably comes from some other outside cause, and thus is not an intrinsic system limitation.

Yolanda Broad Jul 17, 2013:

Opacity, rather than noise? It looks like this is some kind of masking effect, not a kind of white noise.