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Basic Adjustments and the Histogram Panel in Adobe Photoshop Lightroom 2

Contents

  1. Correcting an overexposed image

Article Description

Martin Evening explains how to make some basic adjustments, including correcting over- and under-exposed images, and Tone Curve controls and zones.

Correcting an overexposed image

Lightroom has the ability to reveal highlight detail that might otherwise have remained hidden. You can often recover seemingly lost highlight information by combining a negative Exposure adjustment with the use of the Recovery slider. It may be possible to use this technique on a JPEG image to darken the highlights a little, but this method really only works best with raw images. This is because Lightroom is able to use all of the luminosity information contained in a raw file that is simply waiting to be discovered. In the accompanying example, I was able to recover one and a half stops of overexposure, but in some cases it is possible to recover as much as two stops. As mentioned on page 257, it is often better to optimize the camera exposure to capture as much of the shadow detail as possible, but without overexposing to the point where you are unable to process important highlight information. I will often ignore the camera or light meter readings and deliberately overexpose at the time of capture to record the maximum amount of levels information and use the combination of a negative Exposure and a positive Recovery shift when processing the image.

  1. The photograph on the facing page was first processed using the default Basic panel settings in the Develop module. The histogram shows clipping in the highlights, and you can see how there is very little detail in the sky or building. A histogram like this can appear disconcerting until you realize that there is a lot more information contained in the image than there appears at first sight. Although Lightroom can work its magic on all images, it has a limited effect on pixel-based images such as JPEGs or TIFFs. For best results, you should use this technique when processing raw master files.
  2. Highlight recovery can be achieved by applying a combination of a negative Exposure value combined with a positive Recovery adjustment. If you drag the Exposure slider to the left, you can effectively recover at least a stop worth of information, and maybe even as much as two stops. The downside is that you usually end up making the overall image darker. But when you combine this with a positive move with the Recovery slider, you see highlight information that would otherwise be clipped. I also adjusted the Fill Light, Blacks, Brightness, Contrast, and Vibrance in this shot, but the main highlight adjustment was all achieved using Exposure plus Recovery.

Correcting an underexposed image

Underexposed images represent a bigger problem because there are fewer levels available to manipulate, particularly in the shadows. The Basic panel controls in Lightroom can be used to brighten an image and lift out the shadow detail. But it is important that you work through the Basic image adjustments in the right order, as described in the following images. When adjusting the tones in an underexposed photograph, you will notice that the Blacks adjustment can be very sensitive and a small shift of the Blacks slider can make a big difference to the shadows brightness. In the example shown here I could have opened the shadows more by setting the Blacks slider to 1 or 2. But by choosing 4, I was able to preserve more of the overall contrast.

  1. As with the highlight recovery method earlier, corrections for underexposure should mainly be done by adjusting the Exposure slider first to set the highlight clipping. This should be followed by an adjustment to the Blacks, and then an adjustment to the Brightness and Contrast.
  2. In this example I dragged the Exposure slider to the right, which enabled me to preserve all the information in the highlights. I then adjusted the Blacks so that the shadows were just clipped and used the Fill Light adjustment to radically lighten the dark shadow areas. Finally, I used the Brightness and Contrast sliders to lighten the midtones further and add more contrast depth. What you don’t want to do here is to adjust the Brightness slider before you adjust the Exposure slider. Although similar results can be achieved in this way, you will end up stretching the shadow tones far more than is good for the image. For best results, always approach the Basic controls in the order that I just described.

Tone Curve controls

The Tone Curve controls offer a new approach to tone curve mapping (known as “parametric curves” in Lightroom and Camera Raw 4.0 or later), where the tone curve is modified through slider control adjustments. The reason the Tone Curve controls are presented in this way is to encourage people to make tone curve adjustments based on descriptive criteria. If you are used to working with point curves in Photoshop, the Lightroom method may appear restrictive at first, but the Tone Curve slider controls in Lightroom can often inspire you to create tone curve shapes that are quite unlike the curve shapes you might have applied when adjusting them manually. The slider controls also recognize that a lot of photographers just didn’t get how to work the curves adjustment in Photoshop. The Tone Curve sliders will hopefully make curves adjustments accessible to everyone now, but the good news is that you can still manipulate the curve graph directly by clicking on a point on the curve and dragging up or down to modify that particular section of the curve. Best of all, you can also edit the curve by targeting an area of interest in the actual picture. If you click the Target Adjustment tool button, you can then click over any part of the image and drag the mouse up or down to make the tones there lighter or darker. When you start using this method of tone editing to refine the tones in an image, you won’t even need to look at the Tone Curve panel. You can also use the keyboard arrow keys: The up and down arrows adjust the tone values (note, the left and right arrow keys are reserved for navigating images in the Filmstrip). You can turn off the Target Adjustment tool by clicking the button again or by pressing cmd_alt-shiftn.gif (Mac) or ctrl_alt-shiftn.gif (PC).

The four main slider controls for controlling the tone curve are Highlights, Lights, Darks, and Shadows. The slider controls also provide a shaded preview of the range of shapes an individual Tone Curve slider adjustment will make. In Figure 6.41, I was in the process of adjusting the Darks slider. The gray shaded area represents the limits of all possible tone curve shapes I can create with this particular slider in conjunction with the other current slider settings. For those who understand curves, this provides a useful visual reference of how the curve looks. Plus, you can edit it by clicking anywhere on the curve and moving the mouse up or down to make that section of the tone curve lighter or darker.

As mentioned earlier, the Basic panel is used to apply the main tone adjustments. It important to understand that these are all applied upstream of the tone curve, so Tone Curve is an image adjustment control that you always apply after making the initial Basic panel adjustments. The layout of the tools in both the Basic and Tone Curve panels are also influenced to some degree by the legacy constraints of the Adobe Camera Raw plug-in. For example, recall that the Contrast control in the Basic panel is mainly there to provide a slider equivalent to the one found in the Camera Raw plug-in. So those people who prefer using the simpler Camera Raw method of adjusting contrast can continue to do so. But more important, it has been necessary to ensure that settings applied to an image via Camera Raw in Photoshop will also be recognized (and made accessible) when the same image is opened via the Develop module in Lightroom. I mention all this as an explanation for the presence of the Point Curve menu at the bottom of the Tone Curve panel (Figure 6.42). In the early days of Camera Raw, some purists argued that the tone curve should always default to Linear, and if you wanted to add contrast, it was up to the user to edit the curve. Meanwhile, almost every other raw converter program was applying a moderate amount of contrast to the curve by default. The reason for the default application was that photographers liked their pictures to have a more contrasty and film-like look as the standard setting. Consequently, the Adobe Camera Raw plug-in has evolved to offer three choices of curve contrast; Medium Contrast is the default setting. So the Point Curve menu in the Tone Curve panel is mainly there to match up raw files that have been imported with legacy Camera Raw settings. The Medium Contrast curve applies more of a kick to the shadows to make them slightly darker and lightens the highlights slightly (which you can see by looking at the shape of the curve). The Point Curve is therefore nothing more than a curve shape setting that can be used as a starting point for making further edits to the tone curve, and is mainly there for compatibility reasons.

The Tone Range Split Points at the bottom of the tone curve allow you to restrict or broaden the range of tones that are affected by the four Tone Curve sliders (Figure 6.43). Adjusting each of the three Tone Range Split Points enables you to further fine-tune the shape of the curve. For example, moving the Dark Tone Range Split Point to the right offsets the midpoint between the Shadows and Darks adjustments. These adjustment sliders are particularly useful for those instances where you are unable to achieve the exact tone localized contrast adjustment you are after when using the Tone Curve sliders on their own.

The Tone Curve zones

The Tone Curve zones are evenly split between the four quadrants of the tone curve. In the following step-by-step example, I wanted to show a series of tone curve adjustments in which each of these zones is adjusted. To emphasize how the Tone Curve Zone sliders operate, I have highlighted the active quadrants in green to accentuate the zone regions, and to show which areas of the curve are being adjusted.

  1. I began by adjusting the Highlights slider to make the brightest portion of the image darker and set Highlights to –80. This could have been done in a number of ways: I could drag the Highlights slider in the Tone Curve panel to the left, or make the Highlights field active and use the down arrow key to reduce the value. I could click anywhere in the green shaded section of the Tone Curve and drag the curve downward, or click on this portion of the curve and use the down arrow key on the keyboard to darken the highlights. But in this instance I clicked the Target Adjustment tool button (circled) to make it active, moved the cursor over the image, and hovered over a highlight area on the plate. I then clicked and dragged downward to darken the tones in this selected portion of the curve. Note that you need to drag the mouse up to lighten and down to darken.
  2. Next I wanted to concentrate on darkening the tones within the Lights zone of the curve. I placed the cursor over the table area and again dragged downward with the mouse.
  3. I then darkened the Darks zone by moving the mouse over one of the chili peppers and dragged the mouse downward. If you are using the arrow keys, you can use the alt.gif key to apply small incremental shifts and the shift.gif key to apply bigger shifts.
  4. Lastly, I adjusted the Shadows, which again could be done by dragging the Shadows slider and clicking on the curve to directly edit the shape of the tone curve. But in this case, I placed the mouse over a shadow area in the image and dragged the mouse upward to lighten.