What is the Curves tool?
Curves is a powerful and intimidating tool. For a long time, I limited my adjustments of brightening, darkening and contrast to just the Tune Image and Tonal Contrast tools.
In summary, the curves tool assists to create a more punchy image.
What does the curves tool do?
Similar to Tune Image, Curves controls brightness, contrast, highlights and shadows. You can control the intensity of blacks, white and shift colours in the Channels section of the tool.
The pin in the bottom left corner is the black point. The pin on the top right corner is the white point. Similar to a histogram, the line across the bottom of the graph as dark on the left and ‘bright on the right’.
This article is straight out of the course: "Strategically edit WOW images on your smartphone." Inside the course, I walk you through the power and versatility of the Snapseed app Curves tool. Without the jargon, we explore the when why and how to use this tool. Click/Tap to learn more.
The diagonal line is often referred to as the contrast curve. You can place additional pins along this line and manipulate the shape of the line to make tonal adjustments to dark and light areas of the image. Lifting the curve above the default line will increase the brightness. The extra pins assist to isolate which tonal range of the image will be affected.
You may recall that Tune Image has adjustments for highlights and shadows and does not have control over mid-tones. Ambiance is the closest tool, however it additionally also affects the saturation of colours.
To increase the mid-tones in Tune Image, you need to be a little creative. It requires increasing the brightness, then reducing and balancing the shadows and highlights to create the desired look.
The sand in the above image are the mid-tones, between the brightest (candles) and darkest parts of the image (background). I placed a pin in the middle of the line and dragged it upwards. It increased the brightness of a lot more of the image than intended. Next, I placed pins two more pins either side on the curved line and dragged them back to the middle. This created a more specific curve (bump in the line) exactly in the desired tonal range of the sand.
Adjust the black and white points
Our smartphones capture a limited range of light (dynamic range). This is improving through computational photography (software algorithms). The result for most of us is a dull and washed out image.
Increasing the intensity and amount of black and white expands the dynamic range to create a more impactful image.
Make sure you have the Neutral preset selected first. Next, increase/decrease the range of black in your image drag the bottom left corner pin across the bottom line toward the bottom right corner. Drag the top right corner (whites) left to increase the intensity of white.
Be mindful that the histogram behind the Curves tool does not adjust as you make adjustments! After adjusting the black and whites points, tap on the tick checkmark to create the any further Curves adjustment.
What is the difference between black point and shadows?
Shadows are the darker ‘coloured’ sections of the image, where you can still see some details. Blacks are the black areas without any details. Moving the black point pin does affect the overall darkness of the image. Hence, why you should adjust the black point first – the shadows are tied to that black point.
What is the difference between white point, highlights and brightness?
The white point sets the amount of the image that is an absolute white, instead of a light grey.
Highlights are the brightest parts of the image. Brightness is the whole image brightness. The benefit of adjusting brightness in Curves instead of in Tune Image is you can control how much affect overall brightness actually has on the shadows.
Practical scenario - white point and brightness
The plate in the original below image, had some bright white reflections (hot spots). These were distracting and not aesthetically pleasing. Reducing the highlights in Tune Image resulted in the bright white spots becoming grey and looking blotchy!
In curves, I dragged the white point pin (top right corner) down until the purest white was reduced. Next I placed a pin on the line near the white point (highlights) and dragged it up a little to increase the brightness. This created an upward curve affecting the whole image. The next step was to place another pin near the middle of the line and drag that section of the curved line back to the original straight line. This prevented anything in the shadows being affected by the brightening of the brighter whites.
What is the S-Curve?
Luckily for us starting out, there are some presets available that will add a little contrast (soft contrast) and a bit more (hard contrast).
During this tutorial, we are going to use the below graphic of 10 different tones to demonstrate the direct affect of adjustments on the shadows, mid-tones and highlights.
You will notice when you use one of these presets that two extra pins are dropped on the line producing an S-Curve. An extra pin dropped on the left side of the line and dragged down produces darker shadows. The second pin on the right side and dragged up results in brighter highlights. This increases contrast – the difference between the dark and bright. You can drag these around and even add more pins for further control.
When you make adjustments in Curves, it affects all the colours. Tapping on Channels opens up a few options including RGB (all the colours) and separate colours Blue, Green, Red and Blue. This provides the opportunity to increase/decrease the brightness of colours in different tonal ranges. An example could be specifically darkening the bright blue sky, without affecting the already darker blue water.
Adjustments to the Curves has an impact on the colours. Depending on the image, this could be an undesired effect. That is where the Luminance channel becomes helpful. It allows you to adjust the tonal range - specifically just the lightness behind the colours. A bit hard to explain. This is another tool that I encourage you to have a play and experiment.
As you can see, Curves is a bit of a complicated beast. Many of us experiment and learn by tapping and dragging on dots and lines and analysing the immediate effects. Tutorials and a structured course help you to understand when and why we use these tools and how they work to apply them to really enhance our images.
Love to know how this article has helped your iPhone and Android smartphone photography.
I look forward to meeting you inside the course.
Also published on Medium.