Camera Histogram issue - DPChallenge Forums

03/22/2006 12:46:53 PM · #1

What is purpose of the live histogram in digital camera, i have no clue how to you it for my benefit.
I can understand histogram when we review a picture after it has been taken, one can make out if picture is under exposed or over exposed.

What does live histogram do i dont get it.

I mean to say when i am in apeture priority mode and i see my hisogram changing as i point at different objects. I know how peak of histogram should be in middle. Problem i am facing is i choose aperture say 2.8 and still find histogram peaks is to say to left side, whatever changes i can do ( in my camera when in aperture mode one can only change either aperture or exposure compensation ) the peak still remains .

I have to use studio strobes with my camera , problem is how to use this histogram to find correct expoure

Tamron SP AF 28-75mm f/2.8 XR Di for Canon

03/22/2006 12:53:39 PM · #2

Basically you can't use the live histogram with strobes. If I'm reading this correctly, you're trying to use the histogram with the strobes' modeling lights and they are giving you underexposure readings. If you work with studio strobes a lot, get used to reviewing the test shots in histogram afterwards. And invest in a hand-held strobe meter, that reads the light falling on the subject with test firings, then run the camera in manual mode and dial in the indicated exposure.

Also, to say the "peak" of the histogram "should be in the middle" is not entirely accurate. If you're photographing against a white BG, for example, the peak belongs on the right side; against a black BG, on the left side. How far right or left? depends on the percentage of subject-to-BG and on the lightness of the subject itself.

R.

Canon EOS-20D

03/22/2006 12:55:12 PM · #3

If you're not hitting the far right edge, you can adjust your exposure compensation (+ to move to the right, - to the left) until your histogram ends at that righthand corner.

(Feel free to correct me if I am wrong, please!)

Edited to say: Oh, right. I missed the strobes part. You can't use the histogram to meter for strobes because they aren't on while you're composing.

Message edited by author 2006-03-22 12:56:17.

fotomann_forever

03/22/2006 01:04:59 PM · #4

No, live histogram isn't going to do a bit of good for strobes.

I suggest going to full manual. Set your shutter speed to about 1/250 to start and do test shots, adjusting exposure via aperure. You can then use histograms in review to compare exposures.

FYI, shutter speed has no effect on strobe exposure.

Canon EF 24-70mm f/2.8L USM

03/22/2006 01:08:53 PM · #5

Originally posted by Bear_Music:

You got it right it right ber music, i did not want to buy a flash meter.

Telehubbie

Canon EOS-40D

03/22/2006 01:13:34 PM · #6

It's also useful to show you where on the photo your highlights might be blown out, although I'm not sure if Kodak has that. On mine in historam view, it shows a small thumbnail of the photo next to the histogram and marks any bright overexposed areas.

03/22/2006 01:16:23 PM · #7

Originally posted by mk:

My understanding, which is quite possibly not accurate, is that your histogram should be as far right as it can be without hitting the edge and that the rest of it doesn't really matter.

Like this...

If you're not hitting the far right edge, you can adjust your exposure compensation (+ to move to the right, - to the left) until your histogram ends at that righthand corner.

(Feel free to correct me if I am wrong, please!)

Edited to say: Oh, right. I missed the strobes part. You can't use the histogram to meter for strobes because they aren't on while you're composing.

MK what you wrote about adjusting exposure compensation until histogram peak also responds,well i also felt it should but sadly no change happens , I mean what ever mode i am , what ever changes i can do, those changes are not reflected in histogram, so i find it strange the purpose of live Histogram, Kodak manual is of no use

03/22/2006 01:23:00 PM · #8

Originally posted by General:

Perhaps Kodak's live histogram merely shows the actual distribution of tones in the scene being metered, not the results of exposure changes on the rendering of those tones. If this is the case, I'd be using the histogram to check whether the tones of the metered scene clump left or right; if they clump right, I'd be adding exposure to render them the correct brightness, and if they clump left I'd be removing exposure to render the correct darkness. It would be a useful tool for me even at this level.

Robt.

03/22/2006 01:44:33 PM · #9

Thanks, i will try to understand what you wrote. This is my second digital camera , first one was canon a40, simple country camera as compared to this. I hope i figure out soon

03/22/2006 01:53:19 PM · #10

Originally posted by Bear_Music:

I am not sure if i have got it right, but here what i seem to have understood.

Kodak has live histogram to show how it interprets the scene, and based on that we should do the need ful but are changes are not shown. For arguments sake , if i was shooting at f8, 1/60 and tone are clumped to left than i should say over expose, say either by reducing f stop i.e go to 5.6 or change my shutter speed to 1/30 but these changes wont reflect on my live histogram

03/22/2006 02:03:26 PM · #11

Originally posted by General:

Thanks, i will try to understand what you wrote. This is my second digital camera , first one was canon a40, simple country camera as compared to this. I hope i figure out soon

Let me see if I can explain:

1. When the camera sets its exposure, it assumes that the "correct" rendition of the average of all the tonalities in the image woiuld be a middle gray, what we call a zone 5 gray. It's as if you dumped all the tones in a bucket and stirred, and the result was gray. In the average photograph, this is a valid assumption.

2. The camera has no idea if it is being pointed at something dark or something light. It only reads the amount of light reaching the meter, and cannot know if this is a weak light source reflected off a bright object or a bright light source reflected off a dark object. It only knows that absolute value of the light reaching it.

3. Therefore, if you meter a white wall in sunlight and give the indicated exposure, the resultant image, unadjusted, would be gray, not white. Meter a black wall, give the indicated exposure, you get the same gary. In theory, you can't tell which is which.

4. If your Kodak's histogram is simply showing you the actual intensity of light reaching the meter and its relative distribution (so many pixels receiving "x" value of light, so many receiving "y" value, so many receiving "z" value, etc) then it's still a useful tool even if is not interactive; that is to say, if it does not show changes that would happen with exposure changes.

If you see a histogram like the one MK drew, all spread out evenly, you know the scene's very evenly toned, no contrast issues to speak of. If you get a histogram that's all peaked in the middle with very few outliers, that's a very flat scene that will need additional contrast in all likelihood. And so forth and so on. So you can analyze the histogram, and this will give you indications that you need exposure compensation. If the histogram clumps to the right, the scene has a lot of luminance and you will need additional exposure to render this correctly; the camera will try to pull the bright areas down to gray.

Conversely, if the histogram peaks to the left it has a lot of dark areas, and the camera will tend tooverexpose the scene; you will want to give a little less than th3e indicated exposure. There are a lot of histograms like this in the low-key challenge, and a lot of the other kind in the light on white challenge.

Does this help?

R.

03/22/2006 02:08:14 PM · #12

Originally posted by General:

Kodak has live histogram to show how it interprets the scene, and based on that we should do the need ful but are changes are not shown. For arguments sake , if i was shooting at f8, 1/60 and tone are clumped to left than i should say over expose, say either by reducing f stop i.e go to 5.6 or change my shutter speed to 1/30 but these changes wont reflect on my live histogram

If changes are not showing up on the live histogram, this means it's a "raw" histogram showing the actual light reaching the sensor, not an "interactive" one showing what the finished image would look like when exposure changes are factored in.

This makes perfect sense to me; in geenral, as a photographer, I want the raw information, not the manipulated, predictive information. I have the opportunity to view the histogram of the actual shot after taking it, if I want to see the results.

Robt.

03/22/2006 02:17:32 PM · #13

Thanks but dont you think raw histogram seems to asking alot from photographers like me who have not shot much either with digital and none with film to see a raw histogram and based on that do what you feel is right but yet not be sure if what you done is right. I mean to say ( using my example i above post) if my camera was set f8 and 1/60 and my raw histogram shows me clumps of tones in left and i am expected to over expose , i do by chaning shutter speed from 1/60 to 1/30 and histogram doesnt show if i am doing it right or change in shutter speed is sufficent.May be scene demande me to take shutter speed to 1/15 but i wont know that untill i actually click and see the histogram as weel the actual picture

03/22/2006 02:26:31 PM · #14

Originally posted by General:

Yes, for sure. But consider the price of the camera. What you're asking for is much more sophisticated and more expensive. My point is, this seems to be what you have, and this is how you'd use it.

I don't even HAVE a preview histogram on the 20D; I have to shoot first and examine the resultant capture's histogram before proceeding any further. The 5D and the 30D have preview histograms I think.

R.