Amateur’s Food Photography VI: The Histogram

by Jenn on March 17, 2011

in Photography

Histogram 1

I haven’t done a photography post in a while, but I thought I would get a bit technical with you today and show you something that I started doing not so long ago to help when I take pictures.  This topic isn’t isolated to just food photography either, but can apply to any photo you are trying to create.  When I am taking a photo and trying to figure out the right settings to use, I often rely on reading the histogram associated with each picture in order to assess my exposure.

The exposure of a shot refers to the amount of light your camera let in to capture the image on its sensor.  It does not refer to the amount of light in the room or what is shining on your food.  Controls like ISO, aperture and shutter speed help dictate how much light you want the camera to “see”.  The more light let in to your camera, the brighter a shot will look.  The less light let in to your camera, the darker a shot will look.  I’m not going to get into the specifics of controlling these things today, but instead want to let you know about a valuable tool that you could be using to give yourself instant feedback on the exposure of your shots – the histogram.

When you take a photo and look at it in playback mode on that little screen on the back of your camera, it’s often very hard to see how well the picture came out.  If you are outside in sunshine you’ll probably be lucky if you can see what’s on the screen at all, let alone assess if the image is too bright, too dark, etc.  It’s often frustrating to take a picture thinking it came out great, only to transfer it to your computer later and find out it’s totally dark or bright compared to what you remember seeing it as.  So how does one assess exposure during a shoot?

This is where the histogram comes into play. Most DSLR cameras (and even several point & shoots) these days have the ability to show you the histogram of your shot.  On my camera, when I am in the playback mode, I use the up arrow to display or hide my histogram.   Histograms show a distribution of the brightness of pixels in your photo – on the left side is black, the right side is white, and in the middle is everywhere in between.  Using this information can tell you a lot about how well your camera captured the light of a scene.

However, there is no one shape a histogram should look – as with everything, it depends on the image.  For example, photos with lots of dark regions will have lots of the histogram on the left side, near black:

Screen shot 2011-03-16 at 11.48.43

Photos with lots of bright regions will be the opposite, with lots of the histogram on the right side closer to white:

Screen shot 2011-03-16 at 11.51.20

And photos with lots of midtones, shadows and bright spots will have a histogram with data more spread out across the whole range.  So how does this help figure out if an image is well exposed?

One of the first things I look for when I check a histogram is for clipping.  This is what happens if part of the image is SO far to the left or the right that the data is lost and all you get is pure black or white.  You see this on the histogram because at one (or both) of the edges, will be a giant spike up.  Take for example, this photo of tomato soup (ok, I artificially overexposed it post-processing but it still illustrates the point) –

Screen shot 2011-03-17 at 00.11.52

Do you see how the histogram spikes up on the right side? And if we look at the photo, we can see the garlic in the background is totally blown out.  In this case I think it’s distracting because my eye is drawn to the blown white spot rather than the soup.  If I saw this reviewing the pic in playback mode on my camera, I would retake the shot with a slightly faster shutter speed so that the photo was less exposed.  Regions that are clipped either totally white or totally black in the original exposure cannot be recovered no matter how awesome you are at photoshop – that detail is lost for good.

Some cameras (and some post-processing programs), can even show you exactly where this clipping occurred:

Screen shot 2011-03-17 at 00.12.09

Looking for clipping isn’t the only way to assess exposure.  Here’s a case where the photo I first took was underexposed – meaning it was too dark:

Photographing Roast #5 - Increase exposure

Most of the data is on the way left side, and there’s an actual gap of data on the right – this wasn’t meant to be a dark field image and so this tells me I was underexposed.  Because I checked the histogram in my camera, I was able to figure out that I needed to adjust my shutter speed – to slow it down some to let in more light – the photo on the right shows the histogram for the more exposed photo.  I think I might have adjusted my shutter speed yet again to brighten it even more during that shoot of maple brined pork roast (and now I know the blown spots were on the actually glare on the onions, not from the wall), but these two photos were taken one right after another so I thought were a good example of showing how checking out the histogram during a shoot can help you find the right settings to achieve your desired exposure.

Histograms can also tell you about contrast of an image – here is an image without much contrast:

Screen shot 2011-03-16 at 11.53.03

See how the histogram is squished into a narrow region rather than spread out across the entire tonal range?  It makes sense for this shot, because there really isn’t a lot of contrast in the image.  A high contrast image would have data on both sides of the histogram.  In fact, when you play with the contrast in your editing program, what you are essentially doing is stretching apart or squishing together your histogram to cover a larger or narrower tonal range.

I’ve only given a few broad & general examples here, but the main point I want to highlight is that the histogram is a useful tool to take advantage of.  Understanding what it should look like for your particular shot can help you immensely in determining if you captured the light the way you wanted to.  We’ve discussed in the past about needing good light, but the other part to that is getting your camera to “see” the light the way you want it to :)

Some good links to reading histograms:
Luminous Landscape – Understanding Histograms
Manggy | Special Effects – Understanding Histograms
Matt Wright – Food Photography Post Production

Missed the other posts in the Amateur’s Food Photography series? Check them out here to catch up :)

1 – Look at photos with a critical eye (and making fun of one of my early ones!)
2 – Food photography is about celebrating light
3 – Take your time and find your “zen place”
4 – Angles of Light
5 – Pay Attention to Props