Histogram in your Camera

Well here I am putting my head on the block writing a technical article instead of my usual aesthetic contributions.  My reason for doing this is that the Histogram in the camera is one of the most important revolutionary devices ever built into a digital camera.

In the old days of analogue film photography we had the Hurter and Driffield S shaped curve for estimating the brightness range of the film being used, but it was NOT built into the camera.

The nearest thing to the Hurter and Driffield curve in the digital age is Curves adjustment tool in Lightroom and Photoshop. We all know that if we create an S shaped curve using the curves adjustment tool the contrast in the image is increased depending how steeply sloping the S shaped curve is.

This article is meant for the less experienced members of the club who might not know such a really useful device exists hidden the their digital camera’s menu.

I hope that some of you find the article interesting and use the Histogram to get more accurate exposures and improve your image making.

– Sandy

The sensor in all digital cameras has a dynamic range similar to the old colour slide film which covers a dynamic range from black to white of six or even seven F-stops. Two thirds of the dynamic range information is recorded at the brightest dynamic range of the sensor.

The Histogram can be found in the menu settings of your digital camera and is viewed on the LCD display. Viewing options may include superimposing the Histogram over the picture, or it may be shown by itself. Display options also include a single black and white graph of reflectance, single graphs of red green and blue (RGB) or everything showing simultaneously.

The Histogram is a horizontal and vertical graph that displays where all of the brightness levels contained in the scene are found, from the darkest to the brightest. These values are arrayed across the bottom of the graph from left (darkest) to right (brightest). The vertical axis (the height of points on the graph) shows how much of the image is found at any particular brightness level.

The right side of the Histogram represents the brightness (96 % reflectance) areas of the scene, and the left side represents the darkest (3 % reflectance from the scene).

How the Histogram Works

There is no such thing as a bad Histogram. The distribution of the reflectances will either be clustered to the right, representing a high key photograph, gathered to the left, representing a low key photograph. A Histogram grouped in the middle only means there is a distribution of reflectances from 3 to 96 percent which will show a more full bodied Histogram. Over exposure and underexposure will also affect the Histogram and ultimately the brightness or darkness of the digital image file. Once you become proficient at reading the Histogram, you will be able to evaluate the quality of the exposure based on middle grey. A Histogram shown with the image or superimposed over the image makes the Histogram much more meaningful.

Interpreting the Histogram in the Camera in the Field

There is no standard Histogram for all images, as the Histogram recorded for each image is different. Therefore after you make each image check the Histogram and using the information below, you can if you want adjust your next exposure accordingly. Some cameras even permit you to do this before you make your exposure.

Normal Exposure

Normal exposure is registered on the Histogram when the vertical graph is centred in the Histogram display without it touching either edge of the display. The result can be seen in the camera.s LCD display as a low contrast image. RAW conversion, Lightroom or Photoshop editing software manipulation can recover highlight and shadow details, and brighten up the colour in the image.

Overexposure

Over exposure is registered on the Histogram when the vertical graph is butted against the right edge of the histogram display. The result can be seen in the camera.s LCD display registering clipped highlights as burned and bleached highlights. No RAW conversion or Photoshop editing manipulation can recover all the highlight detail if there was none recorded by the image sensor in the first place. This situation will also show up as blinkies in the Histogram display in your camera’s menu. This flashing indicator shows areas of overexposure in a photograph.

Underexposure

Under exposure is registered on the Histogram when the vertical graph is butted against the left edge of the Histogram display. The result can be seen in the camera.s LCD display registering clipped and severely blocked black shadows showing no detail. No RAW conversion or Lightroom or Photoshop editing manipulation can fully recover the shadow detail where there was none recorded by the image sensor in the first place.

Exposure to the Right

When shooting in RAW format one should try to have the vertical graph brightness levels on the right, but not hard up against the right edge of the histogram display as to cause serious clipping of the image. The image in the camera.s LCD display will appear to be a bit on the light side but do not worry about this as the brightness can be reduced when the image is edited in the RAW converter, or later on in your Lightroom, Photoshop or other image editing software. It is better to try having the vertical graph on the right side but not touching it to get the maximum brightness range detail from the camera.s sensor. Exposing to the right utilises the full potential of the camera.s sensor as more image information is recorded on the right side of the Histogram graph, (approximately 93% of the light reflected from the scene.)

Assessing Contrast

The Histogram can also be used to assess the amount of contrast in the image by how high on the vertical graph it is registered on the scale.

Histogram (Quick Reference Guide)

I found this quick guide in another of my books on photography. You may find it useful to copy it and keep in your camera bag for reference.

  • Set your camera to display the tricolour Histogram (RGB).
  • Single channel Histograms do not tell you if one of the three colours is clipped.
  • Shadows are on the left side, highlights are on the right side of the graph.
  • Ideally you want no clipping on either the right or left side of the graph.
  • If you have to clip somewhere, it it is better to clip the shadows rather than the highlights.
  • If you want detail everywhere in a clipped Histogram, bracket your exposures then merge them together through High Dynamic Range (HDR) software in your image editing software.
  • Keep in mind that in camera Histograms are generated from a small JPEG.
  • You most likely will have more information than is shown in the RAW file, however play it safe by not clipping the in camera Histogram.

© Sandy Wilson 2016

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