Often overlooked, particularly by starting-out photographers and editors, histogram analysis is an integral part of every high-end editing process. It is one of the first stages of it too! But what is a histogram and why is it so important to understand it when deciding on your further editing steps? Let’s take a closer look at what it’s all about.
In Affinity Photo 2 for desktop, you’ll find a histogram in three places: as a panel in the top-right of the UI (both in the Develop and Photo Persona) and then in the Levels and Curves adjustments. On the iPad version of the app, a histogram is present on the Curves adjustment dialog as well as on the Metadata panel.
OK, but what am I looking at?
A histogram presents the tonal and colour channel information (RGB) span for any given image. Forget colour for now (we’ll circle back to it later) and think light only: the far left edge of a histogram is your complete black (0), whereas the far right indicates pure white (1). The areas in between the two will be our shadows, midtones and highlights.
And so, where you see the graph spike, that’s the area where there is more light in a photo. Where the graph dips, those areas are less lit.
How do I decide what to do next?
To answer the question it is best to first know what mood you’d like to communicate in your image. Let’s have a look at a couple of examples that might rule the decision, and how the histogram readout can guide you.
Dark and moody
Looking at the graph for the photo above, we can clearly see that most of the tonal information resides on the left side: this is an indication of our image being underexposed (as seen), with most of the data present in the shadow areas. This is intentional here, and often preferred when working with images typically captured at dusk or dawn.
And so, if that’s the look you’re going for, manipulate it with either one (or a combination) of the following:
- The Black Level slider in the Levels adjustment
- The left side of the graph in the Curves adjustment
- The Exposure adjustment slider
Light and airy
In contrast to the previous look, note that softer, high-key images are represented by a histogram readout that is pushed to the right—a common term used in photography for this type of effect. Perfect for scenes with an abundance of light (typically ambient daylight), and this kind of edit can be achieved by manipulating the following:
- The White Level slider in the Levels adjustment
- The centre area (mid-tones) as well as the right (highlights) side of the graph in the Curves adjustment
- The Exposure adjustment slider
White Balance and Histogram
One of the first steps when editing your digital photos is to ensure you’ve set the correct White Balance, as it will affect your decision-making for subsequent adjustments. Affinity Photo allows you to make that correction via a dedicated adjustment in both the Develop and Photo Persona. However, most starting-out photographers would evaluate the effect of the adjustment on the page by eye and skip observing what happens on the histogram.
Let’s have a look at how paying attention to the histogram helps you set the correct White Balance.
Looking at the image above, we see that the image is too warm with an unpleasant colour cast—this often happens when your camera’s White Balance is set with an incorrect preset, e.g. Cloudy for daylight scenes. Note that the histogram colour channels (RGB) are spread out along the graph. What we’d like to see instead is for them to align, i.e. to be stacked around the same area (below).
Simply use the White Balance adjustment slider and observe the graph values align as you drag left and right, depending on your image.
And so, with the colour channels graph aligned on the histogram, and thus correct white balance set, you can start with the subsequent edits knowing that your scene has been appropriately prepared.
If your captured scenes turn out either over or under-exposed, and you’re wondering how much you’d need to compensate for those while editing, a histogram can help. Look no further than the Levels and Curves adjustments to see how manipulating the graphs can help achieve correct exposure and improve tonal contrast.
With Levels, use the Black Level and White Level sliders and observe how the white lines move on the histogram: try to position them close to where the initial histogram data starts to spike. Similarly, on the Curves adjustment graph, push the bottom-left and upper-right nodes inward, closer to the graph’s data and observe changes in tonal contrast to arrive at a point you’re happy with.
For a deep dive into how a histogram can be used in professional colour grading, why don’t you check headshot photographer Ivan Weiss’ Creative Session video, where he presents creative colour grading techniques with Affinity Photo and offers free content to get you started!