Mastering your Canon camera - the histogram

October 14, 2013

I consider the histogram an essential tool for properly using a digital camera. In fact I would be happy if there was a mode that just showed a big histogram on the LCD screen. On the other hand, it is handy to see the image to check for blinking highlights. One thing is for sure, and that is that you cannot use the LCD screen to judge exposure or image focus and sharpness.

Turning on the histogram

On all of the cameras, near the bottom left corner of the screen is a box with a blue triangle on it that points to the right. This brings up the latest image taken on the LCD display. You can choose just how that image is displayed using the "INFO" button on the 20D and 5D. Pressing "INFO" cycles through 3 options on the 20D: The 5D and 1D add a fourth option which adds separate red, green, and blue histograms. On the 1D, the info button is up above the LCD next to the "menu" button.

Highlight warnings

Sometimes these are called the "blinkies". You absolutely should turn these on. What this does is to cause any part of your image which is overexposed (i.e. the pixels are as bright as the sensor can measure) to blink and catch your attention. Typically you then use exposure compensation to reduce the exposure or decide that you just don't care if that part of the image is clipped and saturated.

On the 1D and 5D cameras, you select enable for Highlight Alert, which is in the fourth menu from the left. On the 20D, it is on all the time as near as I can tell.

Understanding the Histogram

Do not be afraid of the histogram, it will be your friend. If you already understand the histogram, skip the next paragraph.

Your camera has a little computer in it. It looks at every pixel in the image and counts how many pixels have a value of 0 (completely black), how many pixels have a value that is as big as it can get (completely white), and every value in between. Then it draws a little graph that shows on the left how many all black pixels there are, and on the right how many all white pixels there are. This usually takes a while to sink in if it is new to you.

The main thing I do when I glance at the histogram is to be sure that it is as far to the right as possible without actually being crammed against the right side. If there is a gap, I use positive exposure compensation and take the shot again. If it is mashed against the right, I use negative exposure compensation and repeat the shot. I repeat this process until I am happy.

Feedback? Questions? Drop me a line!

Tom's Digital Photography Info / tom@mmto.org