How to Get the Perfect Exposure Using Your SLR Digital Photography Cameras Histogram

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The most important tool in digital photography besides the camera - the histogram! Learning to expose photos properly can be a headache for new photographers. If you are relatively new, you are probably using your cameras automatic functions to shoot most of your images. Not only is this a poor habit to get into but you are wasting some of the extra $1,000 or so that you paid for a digital SLR vs. a normal digital camera.

Steps

  1. Understand what a histogram is. A histogram is essentially a stack of pixels for each tonal value between 0 and 255.
    • A histogram is a digital representation of the tonal values of your image. As you may or may not know, a digital camera works similar to how a computer screen works. There are 256 values ranging from 0 - 255. Please note when I use the term tonal value, I am not referring to color. Color (or hue) is represented by three values RGB (Red, Green & Blue), while tone is represented in the numbers 0 - 255. To get a hue you actually take the values of each color and add them together. For instance, a color Red: 200, Green: 125, & Blue: 60 would produce a darkish orange-brown. A lot of red, a little more than half of that green and about *half of that blue. So, that hue, which turns out to be a hue of 20 will always be that orange color and can be made more or less saturated and more or less bright but the main hue is the same.
    • If you were to take a bunch of ceramic tiles and make a motif and you only used gray tiles with values from 0 (Pure Black) up to 255 (Pure White and everything in between (128 being middle gray, etc), you would have a good representation of how a digital camera sees an image. Now, you have a gray scale motif of hundreds of tiles on a wall. If you were to now walk up to that wall and knock all the tiles off and then stack them in their respective colors, you would have a "histogram" of that image.
  2. Find your cameras Histogram Function. If you can not find it, refer to the owners manual probably under "Manual Exposure" On a Canon EOS, there is a button on the back of the camera next to the image review screen that says "Info". Press that while reviewing an image you just shot from your shot list.
  3. Once you have found the function turn it on and look at how the graph displays in the viewer.
  4. Read the next section for the explanation of how to use the histogram to gauge a proper exposure.

Tips

  • So, you stack all the black tiles tone 0 in one pile all the tiles that are one tone lighter than black tone 1 and so on all the way to white and there are all stacked in order in a straight line, that is a histogram.

A Histogram Example

  • Reading a histogram. Lets now assume that the motif you made was of something with predominately light tones. Something with more light tones and whiteish colors. You would have one side of the histogram with more tiles than the other. The shadows on the left side of the histogram would have less tiles stacked up but the highlights on the right side, those piles would be taller.
  • Each tile represents one pixel. On a digital camera the height of the stack represents the number of pixels in relationship to the overall image that are that color. So for example if you were to take a picture with the lens cap on and look at the histogram, you would likely see one stack of pixels all the way over to the left side of the screen. I say likely because in a perfect world all pixels should be black but sometimes you get erroneous things happening inside the camera that cause a pixel to be a different color than it should be. Most of the time, you would not notice anyway. If you had one red pixel on your screen, even though you might see the pixel when you load up the image on your computer and increase the size 400 percent, you probably would not notice it in the histogram on your camera.
    • Now, if you took a picture of a white piece of paper on a bright day you are going to get a lot of higher stacks on the right side because most of the pixels will be bright colors.
    • Your goal in taking pictures with a digital camera most of the time will be to make sure that your spikes of dark and light are not going beyond the left or the right side of the screen.
    • Yes, it is possible to take a picture inside of your lens cap and get a proper exposure, depending on your f stop and shutter speed setting. There would not be any detail to see and most of the pixels would be on the dark side of the histogram but you could probably pull it off.
    • Since we do not want to take pictures of the inside of our lens caps for the most part, we wii not go there.
    • The histogram tells you if you have lost any detail in the shadows or the highlights by being underexposed or overexposed. This is something that you look at after you have taken the picture so you will know then. The question of how to set your camera before the shot is another conversation and another lesson. For now, get familiar with the use of the histogram in producing exposures that are normal
    • Here we have three examples of histograms. You can see the relationship with exposure in each. An overexposed image will lose detail in the highlights and underexposed image will lose detail in the shadows. You can tell when your images histogram has all it is pixels packed over to one side and the stacks towards the side are higher. It looks like the histogram has shifted outside of the frame.
      • Not all histograms will look the same as the color values in each image will be different. However, if the pixels look like the spike off one side or another, you can bet you are going to lose detail.

      Things You will Need

      • SLR Digital Photography Camera
      • Your Cameras Owners Manual

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      Sources and Citations

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