This is the same raw file if you can believe it.
I realize different programs do different things but I never expected this much variation...
[img]/cfs-file.ashx/__key/CommunityServer.Components.UserFiles/00.00.00.29.05/428W7470_5F00_DPP_2D00_ACR_5F00_hist.jpg[/img]
Sure, I believe it. But it's not a valid comparison, I think. You're actually looking at different types of histograms, comparing apples to oranges so to speak.
The DPP histogram you're looking at (on the RAW tab) is pixel luminance represented on a base-2 logarithmic scale (meaning each 'unit' in that -10 to +4 range is a stop of light, i.e. 1 EV, as you can see when you use the brightness adjustment slider). The ACR histogram is an RGB histogram on a linear scale (0-256 for an 8-bit image, 0-4096 for 12-bit, or 0-16384 for 14-bit). Log vs. linear are very different ways to represent data.
If you want to compare the same type of histogram in the two programs, use the DPP histogram on the RGB tab instead of the RAW tab - you'll find that one looks quite different from the RAW tab histogram, but much more like the ACR histogram (without the secondary colors - cyan/yellow/magenta - superimposed on the display).
Ah - thanks! and thank goodness there's a reasonable explanation, even if the answer only adds more confusion...
Originally Posted by neuroanatomist
I've been through the Help and I see nothing about the histo using a log scale. Am I just missing it? I'd like to make this knowledge useful but I don't understand how it helps me...(I do understand - at least basically - what a log scale is and why it's used)
Are the units you referred to the spaces between the vertical dotted lines?
Moving the Brightness slider to the right, from 0.0 to 1.0, moves the tones to the right but not an entire "unit" to the right.
Does the first 3 spaces on the left being so much skinnier than the rest of them have anything to do with anything? Why are they so much narrower? Why is one of the dotted lines in bold? And what's with the gray sections at either end? Are they aesthetic only? But then why are 3 of the units in the gray sections?
Better yet - why can't I find the answers in Help?? Arrrgh!
Thanks for your help!
I think the rationale for using a base-2 log scale here is simply to convert the luminance data to 'stops' - i.e., a change of one unit means a doubling of the intensity of that pixel.
The units are the numbers along the bottom; the dashed lines are every two units. So, changing the brightness sliderfrom 0.0 to 1.0 for your image will move the largest peak on the histogram from about -1.0 to about 0 (a change of one unit).
The spaces on the left aren't narrower, the dotted lines are still every two units. The solid line at -9.0 isn't a division, that's the black point of the histogram; it's actually a moveable slider - you can drag it, and when you drag it into the portion of the histogram with pixels you'll see the contrast of the image change.
The dotted line at 0.0 is bold because that's the 'origin' - in this case, I believe that zero point is middle (18%) gray as the camera would meter it.
The gray zones at either end aren't just aesthetic - they represent areas of the histogram that fall outside the dynamic range of your camera's sensor. You shot this with an original 5D, correct? That has a 12-bit sensor, while newer cameras have 14-bit sensors which gives them a wider dynamic range. You can see that represented in a comparison of the DPP RAW histogram for a 40D (14-bit) vs. 5D (12-bit):
Hope that provides some clarity - I have not idea why nothing along these lines are in the help documentation.
neuroanatomist,
Does your 40D really go all the way beyond -10EV ?
That´s strange. My 50D goes to -9EV and so does all the latest EOS models. I know this is a technical representation of the max dynamic range the sensor is capable of, defining "usable" DR below the gray point is another subject.
Sorry, but it's not my 40D. [:$] (I have a 7D, and had a T1i before that).
I pulled the image from this article comparing 12-bit and 14-bit images.
But, in DPP with images from my 7D, there is no gray space on the left side, i.e. it's white all the way over, past -10.0. In fact, I may be wrong and this may not even be an approximation of sensor dynamic range, but rather just a function of the version of DPP - from some other articles online (especially one by Doug Kerr), it seems that an older version of DPP went from -9.0 to +3.5. I also ran across a post indicating that an even older version of DPP (v1.6) had actual luminance values on the scale as well as the EV numbers - those numbers ranged from 0-4095 (which makes sense for a 12-bit image - 2^12 = 4096).
Thanks! Very helpful indeed. DPP's Help really doesn't do that program justice.
Actually it's a 1DsIII capture (24-105 @ 28mm, 1/60 @ f/6.3 ISO 1600) inside B&H yesterday. Correct me if I'm wrong but I think that uses a Digic III (or maybe two of them?) at 14 bits/channel. In any case I understand now what the gray areas are for - almost.
The "almost" is this: your screen grab shows the wider DR of the 40D added (only) at the low end. Is that a "real" reflection of where the added DR is (from a 14-bit vs a 12-bit sensor)? So the 40D should be better than the 5D at capturing noise-free detail in the shadows but not any better at holding HLs?
canoli,
If you turn on HTP you will see a shift in the histogram, the highlight end will move up 1EV to around +4.6EV above middle gray, giving you about one stop better highlights, but at the same time the bar marking the shadow end will also move one stop up from -9EV to -8EV below middle gray.
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