Monochrom histogram divisions: what are they, really?

[elgenper]

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This can't be the answer.

 

I have just shot a three image test, low, medium, and high contrast and the divisions are all in exactly the same place, and it's the same place they have always been. I get eight segments, and counting the end lines of the histogram nine lines.

 

I've never seen nine segments as Nick S reports, I've never seen them move, they are always in the same place as wjkotze's examples above. It cannot be contrast dependant where the lines/segments are. The only consistency is that photographing a mid grey card the peak of the histogram is always on the sixth line from the left (or the fourth line from the right, including the end lines of the scale).

 

Steve

 

Now, if I understand you correctly, you´ve found that the position (and number) of the dividing lines is constant for the camera, and thus independent of the image content? Since I haven´t made ´screen dumps´ of the histograms, I haven´t noticed this; from now on, I´ll be more observant.

 

If this is indeed so, most of us are barking up the wrong tree when trying to vary the image and see what happens, of course. In that case, the irregularity must indeed be a firmware bug. Only, one would have thought that they wouldn´t manage to f--k up a simple thing like ten equidistant lines…..

Edited January 10, 2014 by elgenper

[Aperture 2]

No progress with this question ? I'm still in the dark...another thread answered ?

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[elgenper]

No progress with this question ? I'm still in the dark...another thread answered ?

 

Afraid not...

 

However, after using the camera for ten months, I've come to trust it; as long as there is no clipping at the high end, the zones are all there, and post processing get them rendered the way they should. And, after all, that is what matters!

[algrove]

I always consider each division of the histogram to represent 1 EV no matter how far apart they are speced. Since mine shows 11 sections I assume that is 11 stops of DR.

[elgenper]

OK, since the thread has become active again, I decided to make a test series. I did exactly what one did when calibrating a film for the zone system in the old days: I set up a Kodak gray card in even daylight illumination, mounted a reasonably long lens (90 mm) focussed to infinity, and set to a medium aperture. Then I metered the exposure and set the shutter accordingly; this was zone V. By changing the shutter in whole steps, I made 11 shots with the gray card ´placed´ in each zone from 0 (5 steps under) to 10 (5 steps over). Of course, I shot raw, and at base 320 sensitivity.

 

Then, I went through these 11 shots, putting the camera display in histogram mode, and making a photograph of each display with a small p/s digicam. The results are shown here. (Sorry, just too many to embed in the thread).

 

There are imperfections in my method, as I´m the first to admit. Slightly uneven illumination plus some lens vignetting has broadened the histogram peaks (ideally, they should have been spikes); also I stupidly left the clipping indicators at my usual settings (2%/98%); they should have been turned off, even though they don´t really influence the results.

 

A few things are obvious from the series, though. First, those division lines are indeed in the same positions for every shot. Second, the positions of the peaks do not follow the divisions, and since the peaks are demonstrably 1 EV apart, the divisions aren´t.

 

As for more practical conclusions, it is clear that there isn´t much headroom left above zone V; zone VIII (3 steps over) is already totally clipped. OTOH, not even zone 0 (5 steps under) is completely black; there is still some image info there, even if it´s heavily compressed.

 

Now, how correct is the histogram in showing what´s really in the image? To find out, I imported the raw files into Lightroom 5.6 (process 2012) and looked at the brightness values in the center of the images. They were:

 

Zone Brightness (%)

O 2

I 5

II 10

III 22

IV 38

V 59

VI 79

VII 93

VIII 100

IX 100

X 100

 

which is reasonably consistent with what the camera display says.

 

A few conclusions about actually using the camera: First, zone V (normal exposure) gives a noticeably lighter result than the gray card itself (turning on soft proofing and comparing with the grey card showed that it corresponded roughly to the zone IV shot when viewed in my normal viewing illumination). Second, placing things like snow, white petals (or dresses), or whitewashed walls higher than zone VI is asking for trouble with burnt-out areas later on. The celebrated ´expose-to-the-right´ rule is clearly rather dangerous, at least with this camera!

 

Finally, and most relevant to the theme of this thread: whatever those divisions are, they do not seem to give any useful information whatever... The histogram itself, however, is a good indication of what will actually happen in Lightroom after importing the files - and that´s the one important conclusion I can make from this test session!

 

Finally, I´d like to thank all who contributed to the thread.

Edited October 9, 2014 by elgenper

[Aperture 2]

It is very sad that such a visible think has no clear explanation on the manual, if no one in this forum has been able to answer it is not an obvious question. Maybe it is not critical but it annoys me a lot to have it in front of may eyes and do not understand...I get the feeling that I'm missing something. But, ok I will survive