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reading the graph


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#1 yahsemtough

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Posted 07 November 2002 - 07:08 AM

I read somewhere on one of these forums that if a gap exists on the right the picture was underexposed and if it spikes on the right it was overexposed.

Does anyone have any other tips on reading the graphs and examples of what a person should be working to obtain in the graphs after adjustments?

Yes, ultimately it comes down to what the picture looks like as opposed to the graph but...

Is there a "perfect" looking graphs for certain types of shots? It may help in analyzing the adjustments
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#2 herbko

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Posted 07 November 2002 - 12:27 PM

I read somewhere on one of these forums that if a gap exists on the right the picture was underexposed and if it spikes on the right it was overexposed.

Does anyone have any other tips on reading the graphs and examples of what a person should be working to obtain in the graphs after adjustments?

Yes, ultimately it comes down to what the picture looks like as opposed to the graph but...

Is there a "perfect" looking graphs for certain types of shots? It may help in analyzing the adjustments

I think I wrote that. It's a little over simplified, but a good first pass at estimating exposure. The "graphs" ( levels, histogram ) is a plot of the distribution of captured light intensities.

If you have a big spike at the right ( brightest ) edge, that means large areas of the photo is completely white. Of course you could have a large object in you photo this is just white, or more likely you're shooting into the sun, With a digital camera it probably not possible to not have part of it completely white and have the rest exposed properly. Other than these cases, you've probably over exposed the shot.

If you have a gap at the right, you did not make full use of the dynamic range of the CCD. You could have increase the exposure and still gotten all the details of your shot in. For most shots, it's good to fill the whole range without clipping ( spike on the right side ). On rare instances your frame may be mostly fill with something that have uniform brightness and color, which would cause a big peak and make it hard to fill the distribution.
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#3 james

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Posted 07 November 2002 - 01:09 PM

Todd,

Here's a thread which specifically addresses your camera and getting the most out of it:

http://www.dpreview....message=2529814

and another Vincent Bockaert article about histograms and how adjusting brightness and contrast affects them:

http://www.vincentbo...stogram_pix.asp

Hope that helps.
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#4 wetpixel

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Posted 07 November 2002 - 02:15 PM

Here's a shot raw from a D60, with its associated histogram. I consider this well-exposed. I have a lot that are under-exposed, though. Shooting manual is hard! ;)
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#5 james

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Posted 07 November 2002 - 02:48 PM

Perfect example Eric.

If you'd have shot that one using TTL the shark's belly would probably be over-exposed. If he'd done that (Take note Todd...;) ) then there woule be a big block in the histogram on the right side.

Cheers
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#6 wetpixel

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Posted 07 November 2002 - 03:34 PM

Here's raw D60 output that is underexposed:
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#7 wetpixel

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Posted 07 November 2002 - 03:38 PM

I had to dig WAAAAAY back to find an overexposed picture, but here's one. It's quite exaggerated. It's with my old Coolpix 990, Ike housing, and Substrobe 200 on TTL. Man, I sucked then -- and it was only a year ago. ;)
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#8 wetpixel

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Posted 07 November 2002 - 03:43 PM

And, here's that underexposed shark photo, "fixed" in Photoshop. I did an "auto-levels", followed by a fade auto-levels of about 50%, followed by an "auto-contrast", and then a bit of curves tweaking. Quick & dirty. Notice that the levels have been stretched out to fill the entire dynamic range, and that there are now "holes" in the histogram.
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#9 craig

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Posted 07 November 2002 - 05:50 PM

Hmm...
Posted Image
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#10 wetpixel

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Posted 07 November 2002 - 09:42 PM

craig - yeah! yours looks better. mine has a bit too much of the reds and greens creeping in. I did it in 30 seconds, and didn't tweak the color at all. ;)
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#11 snoack

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Posted 08 November 2002 - 02:00 AM

Another hmmmmmm,

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#12 yahsemtough

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Posted 08 November 2002 - 06:31 AM

Thanks for the examples Eric.

The links provided great examples and explanations also.

Where do you guys find these rare and ellusive green reef sharks?

Just kidding. Basically get it right like the first one and you have no problems is the moral of the story. Thus, another Shark expedition.
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#13 craig

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Posted 08 November 2002 - 06:38 AM

The main adjustment was using the channel mixer to blend green into the red channel. I used :
red-red: 85
red-green: 50
I then did some slight rebalancing and setting of brightness which I don't remember. If I stuck with it I could have remved the pink from the face, but I was really trying to make the scene look properly lit and the pink seemed OK.

There are a lot of ways to do this but most will look harder than mine. My approach works well here because of the relatively colorless subject. This turns out to be a nice looking short. Who knew?
I love it when a plan comes together.
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