Understanding the Histogram!

30 Jan

From the Prinsendam off the Coast of Chile!!!

 

Hello all!!!  I don’t think a day goes by on this job that I am not asked, “What is this and why is my camera showing this?” and it’s generally followed by, “How do I get rid of it?”  Well that is easy enough.  Most cameras have a button marked with “DISP” this is the display control and it will rotate through screen options.  If your camera does not have a “DISP” then look for a “Info” button or Nikons might uses the center of the Directional pad as a display option button.  Now to answer the “What is it” question.

That graph you are seeing is called a Histogram. 

Well as I define it and most simple definitions define as is in reference to photos is:

image“A histogram is a visual representation of the quantities of values in a photo relative to the whole.  The height of the line or peak is an indicator of the amount of that value contained in that image.  The highest point represents the greatest quantity in an image.  Gaps and low point mean that little or no values are contained in that shade of grey or value.”

 

 

 

Let me explain that too.

A value is a shade of grey including pure white and solid black.  You use the term value because we are talking math here.  It’s quantifiable percentage of the image.  Now as far as photography, or additive synthesis, is concerned you can not express color in pure white or black, as white is the sum of all colors and black is the absence of all light and color (it’s the opposite of what they taught you in school with colors on paper or using pigments, that’s subtractive synthesis).  So that means to express color and detail you can only do it in a shade of grey.  Notice that there are 3 vertical lines that run through the histogram, those represent the quarter values. 25% grey (Highlight Tone), 50% grey (Mid-tones), and 75% grey (Shadow Tone).  Now how to put that to use using Windows Live Photo Gallery!

In my classes I use one image in particular in our Creative Photo Editing class.  Let me step you through what I do.  I always start talking about this image by asking, “Is this picture a good final image?  Do you like it?  And do you think it could be better?”.

image

Inevitably most people are quite pleased with the way it is.  We can talk ourselves into many things.  So I follow with, “Do those look like rain clouds to you?  Let me ask another way, What color or shade should a fluffy white cloud be to you?”.  Of course the say white.  I’ll then follow as, “What color is our cloud?  Bear in mind the area around the image is pure white”.  The reason I mentioned that we can talk ourselves into things is that we know that is a white cloud so we see a white cloud, but it certainly not.  And if you were to read the histogram you could see that.   

Let’s read this histogram together so you can see how to read your own better.  Remember practice make perfect and experiment.

imageimage

Starting in the bottom left, the shadow end of the histogram (remember the far left edge is black), you will see a small wedge of information.  That corresponds to the center of the flower.  Which I find far to dark.  It is hard to see and feel the texture in an object that dense or dark.  We will fix this in a minute using the Shadow Adjustment Slider you will see directly above the histogram in the Exposure adjustment pane.

imageimage

Next you have the highest spike in the histogram and corresponds to the sky.  The greatest quantity of a value in the image which is the sky.  Which I might add should not be so low in value.  The sky is almost as dark a blue as a shadow. 

imageimage

Following that the is the 3rd highest peak of data in the histogram and that is the dark or shadowed area of the yellow petals.  Then there is a little up and down play and simply that is the stem and the transitions between values.  Nothing really definable. 

imageimage

Lastly we have a small rise around the 25% mark and then the 2nd highest peak.  These refer to the backlit portions of the yellow petals and most important the not-so-white fluffy white cloud.  Now remember that the far right hand side of the histogram is pure white.  Looking at the histogram you can see that our cloud is around 14% grey.  Now that is not white enough for a sunlit white cloud.  It should be white.  Now I don’t think that it should be pure white.  It needs a little grey so we can feel the roundness of it. 

So this is how I correct this image using the histogram as my guide.

First, in the bottom left and right corners there are two little tabs.  They can be slid left and right to set the black point and importantly for this image, the white point.  See, you can tell WLPG where you want white to start in the image.  It’s a hard concept to wrap your head around at first but practice and it will make more sense with time.  Now I slid the White Point set tab next to the where the cloud info starts in the histograms.  Again I don’t want to touch the info and “Clip” image data.  I don’t won’t a floating piece of paper in the sky.  I want a clean bright cloud that feels round and soft.  You will also notice that the sky and the sunlit petals have brightened a little too but that the shadow area has not been affected.

imageimage

Time to fix that blocky dark center.  This doesn’t have to much to do with using the histogram to “fix” Image other than using it to note that what we determined to be the center of the flower is in the lower half and black sections of the histogram and that is far too dark to exhibit good detail.   So this is how you fix it.

imageimage

With the shadows opened, you can now have a sense of texture in the center.   Also note that the sky has brightened and now looks a true sky blue.

 

So a side by side comparison.  You judge which you like better.

Before –

image

After-

image

Now to use the one on your camera that brought this whole topic up.  You can use it to see if you are losing detail in your sky or that you shadows are all blocked up by looking at the Histogram and seeing where your values are.  Now, I have heard a lot of people say there is a perfect shape to a histogram, that all the data should peak towards the middle….  Now that has to be one of the most useless statements I have ever heard.  Disregard it entirely and anyone who tells you otherwise is one of least creative individuals or at least one of the most poorly informed and lacking in logic individuals to speak nothingness aloud.  Question, now that you know how to read a histogram, if you make a photo of snow, which we all know to be white, where should the info in the histogram be?  Yes that’s right in the white and highlight section of the histogram.  Now go shoot something!!!!!!!!!!!!

 

– Will Bossen

Techspert – MS Prinsendam

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2 Responses to “Understanding the Histogram!”

  1. doreen sheinman January 30, 2012 at 4:59 pm #

    Thank you, but none of the diagrams opened. Can you tell me if there is a way to do so?
    Appreciate these info pages!!

  2. Glenna Segall February 1, 2012 at 2:06 pm #

    There were no photos in the Histogram article you posted so it was hard to understand what you were saying in the article. Would like to see the photos to relate to the article.

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