Altman/Henn: Effect of Developer Composition on the Structure of Photographic Images

[Rudeofus]

It is worth noting that Kodak gave up on RMS granularity as a measure of film grain for regular still film image products and went to a subjective measurement system which, they say, better reflects actual conditions.

You understand that the subjective measurement system will never produce numbers like 102% granularity or the like. If this system is still better than the previous RMS based system, I hate to think how uninformative its numbers really are. And I hate to think even more how many scientific papers on photochemistry used that system to make their point.

The whole situation reminds me of the analysis Emili Garcia-Berthou and Carles Alcaraz did a while back when they could show that poor use of statistical tools invalidated a sizable amount of scientific papers in their field.

[albada]

Nowadays we have scanners. My Nikon Coolscan IV ED has 2900 dpi, which is 8.76 microns/pixel. My Nikon Coolscan V ED has 4000 dpi, which is 6.35 microns/pixel. If the optics are sharp enough that they don't degrade the image much, and the focus is accurate, then the scanner is a microdensitometer with an aperture of just a few microns. After scaling a scan to a given contrast, we should be able to run its pixels through some software to compute sharpness and granularity. Or is there a problem with this that I'm not aware of?

For my test-developers, I've simply been posting crops of scans, but I've been thinking of creating an algorithm to produce objective numbers to get away from subjective judgements.

Mark Overton

[Photo Engineer]

If you look at RMSG as a function of density, you see a roughly bell shaped curve with maximum grain ad middle densities and minimum grain at Dmin. You get almost the same reading at Dmax as you do at Dmin in many cases, but in others it is higher.

PE

[Rudeofus]

If you look at RMSG as a function of density, you see a roughly bell shaped curve with maximum grain ad middle densities and minimum grain at Dmin. You get almost the same reading at Dmax as you do at Dmin in many cases, but in others it is higher.

Interesting observation. Since lpmm measurements are frequently made with very high contrast targets, there is a good chance that the lower frequencies record with low granularity. And once the sharpness limit kicks in and densities go towards middle density, grain starts to kick in hard.

[Michael R 1974]

I looked at one of Crawley's film reviews in which he scanned negatives of bars of ever decreasing thickness with a microdensitometer.
He says that main subject outlines are sharper with greater height or amplitude (perhaps that would correspond to adjacency effects) but fine detail definition gives greater amplitude at higher lppm (might correspond to solvent developer where the grains are smaller).
Effect of developer composition would then be shown,not as a number but as a series of charts similar to my sketch,possibly.
But microdensitometer costs >$100k ?

There is some discussion of this in Anchell/Troop (generally very pro-Crawley). When Crawley talks about his developers (and others) he refers to sharpness and definition separately, sharpness pertaining to areas of greater size and definition pertaining to fine detail.

[Ian Grant]

There is some discussion of this in Anchell/Troop (generally very pro-Crawley). When Crawley talks about his developers (and others) he refers to sharpness and definition separately, sharpness pertaining to areas of greater size and definition pertaining to fine detail.

Crawley published his interpretetion of sharpnes, definition etc first in 1960/61 but clarified it a few months later, you need to add the word acutance. It's possible to have a film with high acutance and apprent sharpness that has poor definition.

Ian

[Photo Engineer]

Interesting observation. Since lpmm measurements are frequently made with very high contrast targets, there is a good chance that the lower frequencies record with low granularity. And once the sharpness limit kicks in and densities go towards middle density, grain starts to kick in hard.

The part of the bell shaped curve at Dmax is minimized by density. The high spot in the middle, the peak of the bell is due to the huge mix of fast and slow grains. The grain at Dmin is determined by the fast or coarse grains, and so as you vary emulsions you get a family of bell shaped curves.

The difficulty in the other arena, perceived sharpness, is a factor of resolution and sharpness. This is both a part of the design of the coating itself and the developer. The design of the coating requires anti-halation, acutance dyes in the coating and a number of other measures to improve.

Then there is the factor that is contributed by edge effects which brings up the topic of macro vs micro contrast. If you design the film to have high micro-contrast, then the contrast of fine objects is higher. This film functions well for 35mm. Actually, most films have graded high micro-contrast, medium contrast wider images and lowest contrast for macro images. Thus the transition from 35mm to 4x5 for example, with one film, may give a different visual result in the same developer, but then again, under good conditions, the images should be identical for detail.

PE

[Alan Johnson]

Nowadays we have scanners......... Or is there a problem with this that I'm not aware of?

Mark Overton

My Epson V700 scans a minimum dimension of 2.5 mm, too large to scan a knife edge.

[albada]

My Epson V700 scans a minimum dimension of 2.5 mm, too large to scan a knife edge.

But the true optical resolution of your V700 is probably around 1200 dpi, so each pixel is .021 mm (21 microns). That could scan a knife edge nicely. Kodak's RMS measurements used a 48 micron aperture, which is only 529 dpi. This is why I suspect a scanner could do a good job of these measurements.

Mark Overton

[dpgoldenberg]

If anyone would like to see the original Altman-Hann article, I was able to get a copy. Send me a PM with your e-mail address, and I will send you a pdf.

David