In this solo show Bart explains the effect of each of the photo adjustment sliders in the built-in iOS camera and photos apps. Ever wondered what the difference is between exposure, brightness and brilliance? If so, this is the show for you!
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The native photo editing within the iPhone’s camera/photos app has been steadily improving for years, and is actually quite powerful, but I’ve found Apple’s choice of names for the various sliders very confusing, and I doubt I’m alone in that. Many of the sliders just sound like synonyms, but they actually do quite different things to the pixels in your photos — the canonical example is probably Exposure, Brightness, and their friend Brilliance!
Reminder of the Histogram
Back in episode 55 I described the histogram in an introduction to the more traditional sliders for controlling exposure in most photo apps. This entire episode is worth a re-listen if you want a better understanding of what normal image editors do, and how the built-in iOS apps do things a little oddly.
In that instalment I used the histogram as an anchor for my descriptions, and I’m going to do the same again.
Imagine any image. Each pixel in that image will have a brightness, zero for pure black, and in an 8-bit image, 255 for pure white. Count the number of pixels at each level, then graph those counts on a very tightly packed vertical bar chart with zero on the left and 255 on the right. Most images will look like a mountain when you do this — very few pixels that are very dark, very few that are very bright, and the bulk of the pixels will have brightnesses about half way between the two.
Some Histogram Jargon
Pixels with brightnesses around the centre of the histogram are referred to as the mid-tones, those around the left of the histogram as the shadows, and those around the right as the highlights. BTW, if you ever hear someone talking about quarter tones, they mean the regions between the shadows and mid-tones, and the mid-tones and highlights.
The iOS Photo Editing Sliders
Apple have chosen to arrange their sliders in an order that doesn’t make sense to me. Rather than stick to Apple’s chosen ordering, I’m going to group the settings into related groups.
The Exposure-related Sliders
The standard iOS apps provide 7 exposure related sliders (or maybe 8 if you’re generous).
The first and most basic of these is the traditional Exposure slider. This is a very simplistic adjustment — if you slide left you reduce the brightness of every pixel, and if you slide right, you increase the brightness of every pixel. In effect you’re moving the mountain left or right in the histogram.
Another very traditional slider is Contrast. Like exposure, this is a very blunt tool, it simply mirrors its effect around the middle of the histogram. If you add more contrast you darken shadows and brighten the highlights, and if you reduce the contrast you brighten the shadows and darken the highlights. Something to bear in mind for later is that the contrast slider can have undesirable effects on colours. Increasing the contrast can over-emphasise colours, and reducing the contrast dramatically fades the colours.
The contrast slider affects the entire histogram, in contrast, the Shadows slider lets you control just the left-side of the histogram, brightening or darkening just the shadows, and the Highlights slider controls the other side of the histogram, letting you brighten and darken just the highlights.
The final traditional exposure-related slider is Black-point, and quite unusually, it’s not part of a pair. In every other photo editing app I have ever used, either there is no black point adjustment, or there is both a black point and a white point slider. Anyway, this slider acts as a threshold — all pixels below a given brightness are converted to pure black, effectively slicing a piece off the left of the histogram. To compensate, the remainder of the histogram is stretched to fill the available space, effectively brightening all the other pixels a little.
What might seem a little more confusing at first glance is the fact that the black point slider can go both ways, effectively adding a new piece off to the left of the shadows and then compressing the rest of the histogram to make room and move that new slice in from the the left. Because the iPhone sensor can capture more data than a JPEG can hold, there is actually data off to the left and right of the histograms that can be called into service, so that’s what’s happening here.
If there was a white-point slider it would allow you to slice a piece off the right of the histogram (or add one in), bit Apple didn’t give us one. You can simulate the effect though by adjusting both the exposure and the black-point sliders. To take a slice off the right of the histogram increase the brightness to push the desired amount of the highlights all the way to full brightness, and then use a negative black-point adjustment to pull new data into the left-side of the histogram.
You normally use the black-point adjustment to dramatise the shadows, and the white-point to create a high-key effect, intentionally blowing out the highlights to give your subject a heavenly looking pure white background.
That covers the more traditional five of the seven exposure-related adjustments Apple provides, and leaves us with two very confusingly named smarter adjustments — Brilliance and Brightness.
The icon for Brilliance looks quite similar to the traditional icon fo contrast — a curvy Yin-and-Yang as opposed to a perfect half-black-half-white circle. This is how you can remember what it does — it’s like contrast, only a little more intelligent. If you add more brilliance the shadows darken, and the highlights brighten, and if you add less the opposite happens, just like with contrast, but algorithms are used to tune the effect so it gives you the contrast you want without the negative side-effects that come with the traditional contrast slider. The most important improvement brilliance has over contrast is that is preserves the colours.
Finally, we come to Brightness. The icon for this adjustment look like a sun, and I like to think of it as digital fill light. It brightens the shadows and mid-tones, but it leaves the highlights alone. This is really useful when you’re shooting a landscape on a partially overcast day. Some of all of the ground could be in shadow, but the sky could still have a lot of bright clouds. If you increased the traditional exposure you’d brighten the shaded parts as you intended, but at the cost of all the detail in the clouds. You could compensate with the highlights slider of course, but then you’d be constantly switching between sliders to teak the effect. The brightness slider lets you do it all in one — you can brighten the shaded parts without messing up the sky.
The Colour-Related Sliders
When it comes to controlling colour, the standard iOS apps do provide the traditional three sliders, though one of them does get an unusual name, but they also provide an extra slider that might cause some confusion.
Starting with the simplest and most traditional there’s the Saturation slider which increases or decreases the intensity of all the colours in the image equally. This is a very blunt tool, but it’s useful to get your image into the right ballpark when it comes to colour intensity.
When it comes to shifting the colours around Apple follow tradition and provide a pair of sliders that shift the colour along a pair of orthogonal axes through the colour wheel. If you take the colour wheel and mark red, blue cyan & magenta on it you’ll see they’re equally spread out around its edge like the quarters on a clock face with red at noon, cyan at three, blue at six, and magenta at nine.
As is traditional, Apple provide a Tint slider for shifting the colour along the horizontal axis, i.e. between cyan & magenta. Apple also provide a slider along the other axis, but they chose not to give it its traditional name. Every other photo app I have used names the slider for shifting colours on the red-blue axis Temperature, with bluer colours being referred to as cooler, and redder colours as warmer. Apple kept the metaphor, naming their slider Warmth.
All three of these sliders affect every pixel in the image equally, the one remaining slider, Vibrance is more nuanced. It’s basically an intelligent saturation slider. It keeps skin tones looking natural, and it stops any single colour getting over-saturated. This helps make images really ‘pop’ without looking unnatural.
Sharpness & Definition
A pair of sliders that definitely cause confusion are Sharpness and Definition, they really do sound like synonyms, and that’s probably because they both help to make your image feel clearer. The sharpness slider makes edges stand out more by brightening the highlights and darkening the shadows on each side of an edge. It’s very easy to over-do sharpening and get nasty looking side-effects, so be gentle with this slider!
The Definition slider can be thought of as being a smart form of contrast, making the darker mid-tones darker, and the lighter mid-tones lighter, but leaving the. shadows and highlights alone. The same adjustment is sometimes also called mid-tone contrast.
The last two sliders don’t really map onto the histogram at all, and they do exactly what you’d expect them to, but I’ll include them for completeness.
The Noise Reduction slider applies the desired level of noise reduction. The only thing notable about this slider is that it’s the only one that only goes one way, there’s no such thing in Apple’s app as negative noise 🙂
Finally, there is the vignette slider. This allows you to darken or lighten the edges of a photo. This can be useful for drawing the viewer’s eye to the centre of a photo.