Brief Answer:
In photoshop there are several tools you can use to improve the appearance of detail in your images: Contrast, Clarity, and Sharpness.
The contrast slider adjusts the overall tonal range in your photo, making the lights brighter and the darks darker. The clarity slider is a more intelligent version of the contrast slider in that it adjusts only the mid-tones in a photo.
The sharpness slider affects the contrast at a pixel level. That is, the sharpness slider makes the contrast between each pixel more or less pronounced. Adjusting the sharpness slider can add or reduce perceived texture in a photo.
If you find the above explanation confusing or you want to want a more in-depth understanding of how each slider affects your photos, keep reading.
What is Contrast?
There are two types of contrast in photography: tonal and color. Tonal contrast is the difference between the brightest and darkest areas of an image. Color contrast, on the other hand, refers to the difference in luminance between colors. In this article, when I refer to contrast, what I am referring to is tonal contrast.
The tonal contrast within an image is dictated by its exposure. A photo that contains very dark shadows and very bright highlights will have high contrast. In addition, the location of where contrast occurs also has an influence on the appearance of contrast.
For example, when the shadows are near the highlights, the image will appear to have more contrast than if the highlights and shadows were separated by a gradation of mid-tones. Having the highlights and shadows separated gives the perception that there is less contrast even though there’s plenty of contrast within the image.
Grey Scale
When we analyze contrast, we are always referring to the different levels of brightness and darkness within a photo. The image below demonstrates a gradient between white and black using seven different colors. You can treat each one as a difference in brightness. The shade on the right is pure black and the shade on the left is pure white.
If we include all seven shades in the grey scale above, then the image as a whole will have high contrast. This is because the range between the darkest shade (pure black) and the brightest shade (pure white) is as large as it can be.
On the other hand, if we only include the middle five shades the contrast of the image will reduce. This is because diminishing the difference between the brightest and darkest shades reduces contrast. As the difference in shades within an image decrease contrast will decrease.
The number of different shades of grey in an image will depend on its bit-depth. An 8-bit photo, for example, will have a total of 256 possible shades on its grey scale. While a 4-bit image has 16 possible shades on its grey scale.
Histogram
To determine the contrast in your photo the best way to do this is using an image histogram. I will briefly explain how to read an image histogram here but if would like to know more I wrote an in-depth explanation here.
The right side of the histogram represents an image’s highlights, the middle represents the mid-tones, and the left the shadows. The higher the graph the larger the number of shades that is present in the photo. If the graph is high on the right side, this means the photo consists primarily of highlights. On the other hand, if the graph is high on the left side, this means the photo consists primarily of shadows. If the graph is neither high on the right side or on the left, the photo consists of primarily mid-tones.
Now that we know what contrast is and how to measure it, let’s look at how shifting the contrast slider affects your photo.
The Contrast Slider
The contrast slider applies global changes to all the shades in your photo. This means that when you shift your contrast slider every shade in your image will shift accordingly.
Let’s look at the images as an example. The image below will be our baseline photo. That is, there is no adjustment to any slider has been applied to it.
Increase in the Contrast Slider:
When you increase contrast in Photoshop, you are increasing the entire range of brightness in a photo. That is, you will be making all your highlights brighter and all your shadows darker. This shifts your histogram’s curve to the edges of the graph, resulting in more highlights and shadows. Increasing your contrast slider can also result in clipping and a loss of detail in your image.
Let’s look at the example image below. In this image, I raised the contrast slide to its highest value(+100). The result is a photo that has more contrast than our original photo above.
Notice that, compared to our original image, the tones in the foreground are now more defined. This is because we have added more shades of highlights and shadows which increased the distance between the brightest and darkest tones in the image. The increase in tones within the image by the new histogram, which wider than the original histogram above.
Decrease in the Contrast Slider:
Decreasing the contrast decreases the entire range of brightness in a photo. It also shifts your histogram’s curve away from the edges of the graph, resulting in fewer highlights and shadows. In addition, Decreasing your contrast causes a photo to look dull and flat because everything appears to have the same brightness level.
In the example image below, I reduced the contrast slider to the lowest possible setting(-100). Notice that the different tones in the foreground have decreased. That is because the distance between the darkest and brightest shades has been reduced. The decrease in tone can be seen in the new histogram, which is narrower than the original histogram.
What is Clarity?
Clarity is a tool created by post-processing software companies to adjust the mid-tones of an image.
The Clarity Slider
Clarity and contrast sliders are similar in that both sliders can alter an image’s range of brightness. The way they do so, however, is different. Unlike contrast, clarity sliders increase contrast in the mid-tones only, leaving the highlights and shadows unchanged.
Let’s look at some examples (Note that I will be referring to the same baseline image I used above).
Increase in the Clarity Slider:
Increasing the contrast slider increases contrast in the mid-tones within an image. This increase amplifies tonal transitions and enhances the appearance of overall detail. This adjustment can make an image look “punchier” or even cartoonish if used to an extreme.
In the image below, for example, I raised the clarity slider to its highest value(+100). By increasing the clarity slider I increased the shades of mid-tones present within the photo. This increase can be observed in the new histogram, which is now wider than the baseline image above. Notice that the increase in contrast in the mid-tones also resulted in a more aggressive looking image.
Decreasing in the Clarity Slider:
Decreasing the clarity slider will result in a reduction in the overall appearance of detail in an image. It does so by diminishing the tonal transitions between objects making them appear softer and less defined.
In the image below I lowered the clarity slider to its smallest value (-100). By decreasing the clarity slider, I decreased the number of mid-tone shades present in the photo. This can be seen in the new histogram below, which is narrower than the original image.
What is Sharpness?
Image sharpness is characterized by two elements – resolution and acutance. These elements are determined by factors such as cameras specs, lens used and camera settings used when taking the image.
Resolution is the degree of detail in your image. It is determined by the number of pixels in your camera. Acutance, on the other hand, is the degree of contrast between pixels. It is determined by pixel density (pixels per inch or PPI) in your camera’s sensor. This contrast determines how well the borders between pixels blend together.
Note that focus and sharpness are not the same. Focus is the presence of detail within an image, while sharpness is its level of detail. Unlike sharpness, the focus cannot be enhanced using post-processing software. The only way to improve out-of-focus images is to take another image with improved focus.
Both resolution and acutance cannot be changed during post-processing. The sharpness slider can, however, enhance the appearance of an image’s sharpness.
The Sharpness Slider
Although sharpness refers to both resolution and acutance when altering images in post-processing the sharpness slider only affects its acutance. That is, sharpness sliders cannot change the number of pixels in your image and it can only enhance the amount of contrast present between pixels. It does so by increasing brightness in light pixels and decreasing darkness in dark ones.
Increasing the sharpness slider will make pixel edges more defined, causing an increase in perceived texture. Conversely, decreasing sharpness will reduce definition between pixel levels, decreasing perceived texture. Keep in mind that increasing sharpness can cause an unrealistic and artificial look to your image. It can also amplify the noise present in your photo.
Let’s look at the following images as examples.
The image below will be our base reference.
Increasing the Sharpness Slider:
In the image below I increased the sharpness slider half its max amount (75). You can see that the texture appears to have increased. The light shades within the image have become brighter and the dark shades have become darker. Notice that unlike our previous examples, the histogram below has remained unchanged despite increasing the sharpness slider. This is because unlike contrast and clarity sliders, we are not adding or reducing tones, we are simply amplifying contrast at a pixel level.
Let’s look at another example below. This time I raised the sharpness slider set to its max value (150+). Similar to the image above the texture has increased. However, at this point, the resulting image looks almost unrealistic. The sharpness has been increased so much that the location of the pixels is noticeable.
What’s the difference?
All three sliders, contrast, clarity, and sharpness, have an effect on image contrast. I like to think of them as paintbrushes with varying sizes.
Contrast is a wide paintbrush, adjusting every shade in a photo: highlights, mid-tones, and shadows. Contrast has an impact on the overall exposure and detail in an image.
Compared to contrast, clarity is a finer paintbrush, shifting only the contrast between mid-tones. Sharpness is the finest paintbrush of all three, precisely adjusting contrast between each pixel. Sharpness is a great tool to use if you want to add texture to your image.
