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01-19-2009, 07:09 PM   #1
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Histogram Confusion

I need some help sorting out a contradiction between what my K20D manual says about the ideal histogram curve and what Darwin Wiggett says in a recently purchased book. The manual says the curve should peak near the centre. Wigget says that because 75% of brightness levels are within the first two stops (out of 6) of dynamic range the curve should peak to the right of centre. This will often "look" overexposed on the lcd but actually contains more brightness information to work with in the raw on the computer. What Wiggett says makes sense to me, my only concern is that maybe the Pentax histogram is setup differently - already taking into account the factors Wiggett refers to. Any knowledge out there, is it as simple as "manual good for information about camera but not about photography"?
Mikel.

01-19-2009, 07:27 PM   #2
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QuoteOriginally posted by Mythmaker Quote
I need some help sorting out a contradiction between what my K20D manual says about the ideal histogram curve and what Darwin Wiggett says in a recently purchased book. The manual says the curve should peak near the centre. Wigget says that because 75% of brightness levels are within the first two stops (out of 6) of dynamic range the curve should peak to the right of centre. This will often "look" overexposed on the lcd but actually contains more brightness information to work with in the raw on the computer. What Wiggett says makes sense to me, my only concern is that maybe the Pentax histogram is setup differently - already taking into account the factors Wiggett refers to. Any knowledge out there, is it as simple as "manual good for information about camera but not about photography"?
Mikel.
That's a big subject.. and best just to do some legwork and trial and error on your own. One thing is that apparently (guess it depends on what "experts" you believe) maximising exposure to create a histogram that is right of center is NOT to satisfy the "brightness level" thingy but just to maximize signal/noise ratio. (for a wonderful discussion on all things histogram related see.....
Re: Not really, it's spot on.: Open Talk Forum: Digital Photography Review
Also remember that the histogram is completely based on the jpg created from the RAW file and is modified by your jpg in camera settings, which you may or may not apply in post processing a RAW file.
Now pushing exposures as high as you can, blowing out highlights you consider unimportant if need be, is not a bad thing, as you can always "tone things down" if needed and generally RAW has more head room then even what you see in the histogram, it's just not worth it to sweat it too much, depending on your level of noise acceptance..

Last edited by jeffkrol; 01-19-2009 at 07:33 PM.
01-19-2009, 07:56 PM   #3
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IMHO, it's not a contradiction of logic, but a contradiction of objective. Or even more subtly, means to objective.

Most of the time, the picture will look more "right" if the histogram peaks in the middle.

But by exposing to the right, then using post process raw "development", and adjusting the tone downward such that the peak is nearer the middle will yield a cleaner, less noisy image than the other, ultimately "equally exposed" image.

For me, it's a question of how important is the "cleaner" image? If not so much, meter your peak to where it looks right (middle-ish), and save your jpeg. If you want the absolute best your camera can deliver and are willing put in the "manual" effort required to get there, then EV comp your exposure to push it to the right and be ready to spend the time to perfect it when you get home.

I'll agree that I don't trust how it "looks" on the LCD unless A) I've got my highlight/lowlight "blinkies" enabled, or B) I'm really just using the LCD to see the histogram AND C) I know how I've got my default JPEG conversions setup, since that's the basis for your displayed histogram.

-Chris
01-19-2009, 08:08 PM   #4
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To quote Mr. Wiggett

A Photography Workshop Leader’s Perspective

Some folks get so addicted to the LCD screen that they miss many shooting opportunities. A friend of mine who leads photography workshops for one of the largest photo tour companies in the world says that the digital shooters on his trips spend 80% of their time in the field hunched over their LCD screens missing shot after shot of great light and peak action. Then, to top it off, they miss further opportunities because they are busy downloading, and/or working on their images on the computer rather than being out shooting with the rest of the group. With film, there are no distractions like the LCD screens, laptops, constantly drained batteries, software issues, firmware updates etc., etc., – you go on a trip and shooting is your focus - period. According to my friend, the film photographers are always busy shooting – the digital photographers are, in his words, “always busy dicking around”.

Another professional shooter I know has told me that since he started shooting digital, he’s not as careful to nail the shot in-camera as he was with film. “If it is close enough, that’ll do” he says, I can always fix it in later in Photoshop”. Another shooter tells me in confidence, “I don’t work a situation as extensively when shooting with digital – if I see that I got a shot on the LCD screen, I move on”.

My Perspective

I too have found that shooting digital makes me a little lazy. I often won’t go to the same efforts with digital to perfect the shot in-camera like I would if I were using film. With film, I am extremely careful about contrast control, altering the lighting with reflectors, or fill-flash, or more commonly with filtration (grad filters, warming filters, and polarizers) to make the whole scene recordable on the emulsion. With digital I often have the ‘fix it later attitude’ which in the end creates even more work for me behind the computer. In photo 5a I should have used a grad filter to even out exposure between the foreground canoes and the bright peaks and sky. Had I shot this image on film, I would never have left off the grad filter. With digital, I thought, I can even out the exposure later in the computer – I did (photo 5b) but it cost me a lot in terms of time.

Film vs. Digital

Actually I find that whole thing refreshing..........

01-19-2009, 08:14 PM   #5
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Don't forget what the histogram represents - relative number of pixels in each 1/256th of the tonal range. If your subject has a lot of dark colors, it should not peak on the right (and vice versa).
01-19-2009, 09:44 PM   #6
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There's no such thing as an ideal histogram, at least not in any absolute sense. It's completely dependent on the particular scene and on how you want to represent it. Sure, as a sort of rough generalization, you could say you want the average (not necessarily peak, but average) to be around the center for an *average* scene in order for the image to look right. If the scene is brighter than average, it should be right of center in order to look right. If the scene is darker than average, it should be left of center in order to look right. As an obvious if extreme example, a picture of a black dog in a coal bin should be left of center, a white dog on the snow should be right of center, and a medium brown dog in the dirt more or less centered. But that's in order to *look* right. The whole of "exposing to to the right" (which is presumably what Wiggett is talking about) is not to get the picture to *look* right, but rather, to give you the best starting point for post processing if you wnt to get the most detail and least noise. He'd have you exposing the black dog in the coal bin to the right, which wouldn't look right at all - it would look way too light - and then presumably darkening it in PP.
01-19-2009, 10:18 PM   #7
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If you set the contrast slider as low as possible in the REC setup (for JPEGS), the histogram display (and blinkies) will come closer to showing blown highlights in RAW capture.
01-20-2009, 06:26 AM   #8
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I think there is a lot of confusion about the histogram, and what it shows.

the histogram shows specifically the percentage of the image at each light level and nothing more.

to use it, forst of all, you need to understand the metering.
- Start with a single color uniformly illuminated surface. Meter and expose, and now look at the histogram. It should be in the middle and very narrow. this means that the camera metering is correct.

with any mixed illumination scene, you need to consider exactly what you want correctly exposed.
-a dark bird against a light sky should, if you want any detail in the bird, have the histogram almost all the way to the right, because the sky whioch makes up almost the entire image, is bright. if the sky and histogram are centered, then the image is a silouette, with no detail. The same applies to snow shots.

- in a more neutral scene, you will get a borad histogram, perhaps tending to the right, or perhaps to the left, depending on the percentage of light and dark.

- if you are shooting JPEGs, the most important thing from the point of view of detail, is to adjust the contrast of the scene accordingly to try and distribute the histogram over the entire range. High contrast shots, unless the effect is intentional should have low contrast settings, and when there is flat lighting, you should increase the contrast. this allows the maximum information to be stored in the JPEG for any PP you intend to do afterwards.

01-20-2009, 03:43 PM   #9
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I always laugh when I see people being told what a histogram is supposed to look like. Every different scene has an entirely different histogram. The only thing that should be "right" is your exposure. Get your exposure right and forget trying to get some mid-peaking histogram that some smarmy photographer says you should be getting.
01-20-2009, 07:25 PM   #10
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I use the (in)famous "blinkies". If I have red blinking in the specular highlights, my exposure is what I want. Look up the phrase "Expose to the right" or "ETTR". It is searchable on the forum and should give you results that make sense.
01-21-2009, 12:56 AM   #11
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Thanks Peoples

QuoteOriginally posted by Marc Sabatella Quote
... The whole of "exposing to to the right" (which is presumably what Wiggett is talking about) is not to get the picture to *look* right, but rather, to give you the best starting point for post processing if you wnt to get the most detail and least noise. He'd have you exposing the black dog in the coal bin to the right, which wouldn't look right at all - it would look way too light - and then presumably darkening it in PP.
Most detail, least noise for post processing, yeah that makes sense and is relevant for me because I don't bother with jpgs in camera, just the raw. Thanks for all the input peoples, much appreciated and helped me chew over the issue nicely.
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