Histogram question

[dabber]

I am learning something new everyday with my D70!
I have a question about the histogram in PSE 3. I take my pictures in NEF (RAW). I understand the horizontal range of the histogram but am not quite sure I get the vertical. I know that it is supposed to show how many pixels of each area (color - I think). Now, when you are in PSE studying the NEF file, the histogram shows red, blue and yellow but it also is overlaid with a white histogram. I am not sure what functions I need to adjust for this. Am I supposed to make the colors disappear and be even with the white part of the histogram to avoid "blowing" the colors? Excuse my ignorance, but I am trying very hard to learn.
Thanks,
Debbie

[Grant]

Debbie

Do not be cowered by histograms because they are not a simple as some people thing. First of there are many forms of histogram. For the most part the horizontal will indicate a value of 0 to 255. This will usually be can be things like colour luminosity shades of grey and so on. The vertical value is a representation of the number of counts of a given horizontal number either relative or absolute depending on the histogram.


Now this all sounds complicated but in the beginning instead of thinking of all this mumbo jumbo break it down into manageable bits of information. You will see a curve for you image. Now lets consider a well exposed average contrast image. You will see the curve peak some where in 126 range and gradually fall off to the edges. If you see it peak sufficiently closer to 0 it is an indication that your image is under exposed. If on the other hand the peak falls closer to 255 then this indicates the image is over exposed.

Now I said for average images. If you are photographing a black cat in a dark corner your image should peak closer to 0 and a white fox in a snow bank will peak closer to 255. So knowing your subject you can judge how good you were at exposing.

The Colour curves are also an indication of colour balance and if all even they should fall close to the middle, but a red maple in the fall will not.


So what I am saying is that there are no absolutes using a histogram but it is a tool that can help you gage where your exposure and colour balance should be. Once you get familiar with these guideline there are ways you can use histograms to help you adjust your image for effect.

Grant

Home Pages http://home.cogeco.ca/~grant.dixon

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[Wendy]

Grant,

What a good explanation of histograms ... I have a reasonable grasp of them but your explanation clarified a few thing for me.

Thank you

Wendy

[Grant]

Wendy

Just ask you know I will answer .... well if I know the answer that is. :roll:

[FJBrad]

I can't remember where I first heard this (Kelby or Deke?), but the Histogram was compared to an audio graphic equalizer, wher the shadows are = to bass tones, highlights =to treble, midtones to midrange. I thought this was a helpful way to think about it.

[neil]

Hi there, first of all have lots of fun with your D70, i have one and am really enjoying it. Whilst the previous answers have described what a histogram is, no one has explained what an RGB histogram is. It takes practice to read... but here is one of the best explanations i could find.

http://www.sphoto.com/techinfo/histograms/histograms.htm

Hope that helps.

Best wishes from Switzerland

Neil

[jcochran]

Dabber

This link gives you a really simple explanation of histograms:

http://www.earthboundlight.com/phototips/histogram.html

[Chuck S.]

One other point about histograms, paraphrased from Bruce Fraser's book on Adobe Camera Raw: the camera histogram is a depiction of what the image might look like if saved in JPEG. However, if you're using RAW (which you should in many/most cases), the actual histogram would look much different and areas that appear to be blown out (pushed to the right side of the scale) may have some image information available in RAW that would have been lost in JPEG. So don't give up on a RAW image just because the histogram is skewed right!

Chuck

[Grant]

Chuck

Ah my friend you should know by now that I hardly ever shoot RAW. I am just to stupid to handle RAW ... unless it's sushi :D

Grant