Using The Histogram In Adobe Photoshop Lightroom 4

What Is The Histogram?

As with histograms available on cameras, this graph represents the range of tones that are in the image you’ve taken with the left side of the graph showing the darker tones (shadows) and the right the lightest (highlights). 
The Histogram in Lightroom automatically changes when a new image is opened up and it can be found in the top right of the Develop module.

Why Do We Need To Use It? What Does It Tell Us?

The histogram will help you judge the tonal range of the image and as a result, you'll better understand how to adjust the tones in your shot. There's no one correct histogram pattern you should aim for as all images are different, however a graph which shows the plotted data spread across the full length of the axis (without clipping either end of the graph) rather than clumped together in one area suggests the shot has a better tonal range. Of course this isn't true for every shot as if you've shot a low-key image, the histogram's plot will show a higher grouping of data towards the left-hand side of the graph but there's no point in adjusting the tone of the image to produce a more even histogram as you're trying to create a low-key image in the first place.

Understanding Clipping / Identify Clipped Parts Of An Image

Clipping shows areas of the image where detail is being lost because of blown out highlights or really dark shadows. If the graph has peaks at either end of it that reach up the vertical axis you'll know you have clipped highlights or shadows depending on which side of the graph the peak is. There's two triangles at either end of the graph and these will become highlighted if clipping has occurred.
If you place your cursor over either of the triangles you'll be able to see a preview of where the clipping has occurred in the image. Red shows blown-out pixels while dark shadows appear blue. If you want the clipping preview to remain permanently just click on the corresponding triangle. If you don't want any of the options to be selected, right-click on one of the triangles and un-tick the options you no longer want to be selected.



To reduce / remove the clipping, you need to adjust the tones via the slider or by clicking and dragging parts of the histogram to the left or right (Lightroom then adjusts the sliders for you). If you set it so the clipping preview is always present, you can watch the red / blue areas disappear as you adjust the tones of the shot.

Adjusting The Image's Tones 

If you place your mouse cursor over the histogram the various tonal ranges are highlighted and by doing so you'll also highlight the tone slider that correspond with them in the Basic panel.

You can adjust the tones in the image via the sliders or by clicking and dragging the Histogram.

It's important to understand how each of the sliders will affect the histogram so here's a quick overview on what each slider does:

Exposure: This mainly affects the mid tones but the shadows and highlights are altered slightly. If you move the slider to the right, you'll notice that the who graph moves to the right.

Contrast: Pull this slider to the right and the histogram is stretched out towards the side of the graph with the right extending the shadows and left extending the highlights. It makes highlights lighter and shadows darker.

The Exposure and Contrast sliders are, in a way, the most important as they make the biggest difference to the look of your shot. Do adjust these sliders before you make any other adjustments.

Blacks: These slider controls the tones at the far left of the graph. You probably don't want to remove all of the blacks from the shot, though, as most images work better when they have some areas that are pure black.

Whites: This slider affects the tones to the far right of the Histogram (the opposite to what the Blacks slider does). It's best to adjust the Highlights first then use small adjustments of the Whites to change the brightest parts of the image.

Highlights: This will adjust the tones that are slightly darker than those found in the 'Whites' section and can be used to recover detail lost because of blown out highlights.

Shadows: This adjusts the tones that are slightly lighter than those found in the 'Blacks'.

Two other sliders available towards the top of the panel are 'Tone' and 'Tint' which adjust the colour temperature of the shot. Again, if you move the sliders the histogram will adjust accordingly. Moving the 'Temp' slider to the right will add warmth to the image while pulling it to the left will introduce a colder, blue tint.

For this shot we pulled the slider to the right to add a little more warmth to the autumnal shades:



The 'Tint' slider can be used to put more emphasis on green or pink tones. Again, the Histogram will change to depending on how you adjust the slider. 

If you want to improve your shot further try adjusting the Vibrancy, Saturation and Clarity sliders.

Both Vibrancy and Saturation sliders change how saturated the image appears but work in slightly different ways. Most find it best to start with the Vibrancy slider and then use Saturation. It's also worth changing the Contrast and Clarity sliders before adjusting the saturation because increasing the contrast of the shot will boost its saturation. An image that appears to be very saturated will have strong colours and be bright. The Vibrancy slider won't change colours that are already highly saturated and certain tones won't be affected either.

The Clarity slider gives mid tones more contrast. Pulling the slider to the right will make the image appear sharper and crisper while pulling the slider to the left creates a softer look. The 'less is usually more' motto fits well with this slider as you can see in the examples here:







If you decide at any point that you want to re-set a particular slider you can double-click it to take it back to 0. You can also use the History panel and click on a particular step you want to roll back to.

Compare The Original Shot With The Edited Image: 

As you can see, a lot of changes can be applied to an image before you even approach any of the other panels so do take the time to adjust and play around with these sliders as you can improve an image substantially with just a few small, basic tweaks and the help of the Histogram.

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