"Granular clumping" in graduating areas of tone. What's causing it and how do I cure

[Mahombi]

I'm getting what I can only describe as "granular clumping" in areas of otherwise smooth areas of graduating tone, e.g. sky. This effect is evident in the midtones when levels or brightness and contrast adjustments are applied. It's not dissimilar in appearance to milk separating. It's ruining the smooth tones of the original film.


Can anyone tell me why this is happening and how I can (a), cure it and (b), avoid it in future?



The image is a landscape taken on medium format, black and white IR film (Konica 750). The neg was scanned as a 48 bit RGB image on an Epson V750 scanner. The tone adjustments were applied without converting to 24bit RGB or 8 bit greyscale, to try to avoid my other continuing problem of banding in the same areas.


Thanks in advance.

[Chuck S.]

That really sounds like there aren't enough tones with which to work, and the levels and contrast adjustments highlight the problem by spreading the limited tones over a broader range, leaving gaps in the tonal curve. That's the same phenomenon that causes banding.

You're certainly doing the right thing directionally by scanning at 16 bit (48 bit RGB) rather than 8 bit (24 bit RGB). Are you using any curves adjustments on the scanner itself? I'd be inclined to scan with the scanner curves set to neutral, then do the initial adjustments in Adobe Camera Raw, and finally pass the image to PSE as 16/48 bit for final touch-up.

I suppose it's also possible that the IR film has limited tonal qualities. There's certainly a tendency in some IR films to blow highlights, smudge details, etc. Perhaps the nature of the beast....?

[Mahombi]

Thanks for your input Chuck. I almost certainly did adjust the tone curve in the scan, although I've had the same problem with it flat. I've tried various exposure permutations, all with the same results. Conversely, with a different shot with similar characteristics and on the same type of film, I get no problem.

I can appreciate what you say regarding the inherent contrast in IR film. However, over the years I've managed to perfect an exposure and development regime with the Konica IR film which gives me very good negs. In each case the same shots come up brilliantly in darkroom printing.

Annoyingly, scans from the prints give no such problems. The necessary spotting in Elements after though, is forehead slapping. (I don't like using any dust removal in scans. The resulting softness just seems to render the use of medium and large format film as a waste)

I've got similar grain problems with some scans of colour transparencies. They are subtle but still noticable. The originals were shot on Velvia and this problem just unravels the fine, smooth tonality of the film. Again, it is more prominent when tone corrections are applied.

I've just bought Lightroom and was considering putting it through there first. Do you think that would help?

Mahombi