A Viewfinder Darkly

Photography tips and tutorials

Lightroom Tone Curve for Brightness and Contrast

December 29 2016

by Philip Northeast

The Tone Curve panel in Adobe Lightroom provides another level of adjustment  for brightness and contrast in addition to the Basic Panel  tools.

Why use Tone Curve panel 

The Tone Curve offers  more targeted adjustments than the general  purpose adjusters in the Basic Panel. There is a degree of interaction between the two a sets of adjustments  and the histogram is an essential tool in coordinating the two.  There is no right way to use the Tone Curve in conjunction with the Basic Panel tone sliders.

The Tone Curve is similar to the powerful Curves tool in Adobe Photoshop. The default state  is a much simplified version of Curves,  offering fast easy adjustments, particularly for  photographers new to advanced photo post processing.  The Tone Curve uses four sliders to provide quick adjustments of brightness complementing the adjustments available in the Basic panel. The Tone Curve has  sliders to adjust  the Highlights, Lights, Shadows and Dark sections of the image.

Lightroom screen shot

Tone Curve panel

The difference from the Basic Panel

Confusingly, even though they have the same names the tone adjuster sliders in the Basic Panel are different from their namesakes in the Tone Curve Panel.

The Basic Panel’s Highlights and  Shadows sliders control a complex analysis and adjustment algorithm that Adobe keep improving.   The Tone Curve adjustment is a simple curves adjustment where  the exposure level  in the target region is manually adjusted. The Basic Panel adjusters control the amount of processing applied to the larger target area not  a direct control of the exposure level.  Because of the different scope  and methodology of the two panels they complement each other. It is not a case of one is better than the other, it is usual to use both.

Tone Curve Adjustments

The essence of the curve tool is a graphical representation of  light levels as a straight line from black on the left to white on the right. The height indicates the amount of brightness along the line on the graph. Four slider adjusters raise or lower a segment of the curve, adjusting the brightness in that segment.  The shape of the curve determines where there are contrast changes.  A steeper  curve  results in more contrast.

It is also possible to adjust the positions of the transition points between the adjustment regions.

tone curve

Highlighted region around curve shows limits of adjustment at that point

There is a histogram background on the Tone Curve display showing  the number of pixels at each brightness level. This is one of Lightroom’s indications of where on the curve to apply the adjustments. Another is  pointing to a spot on the  Tone Curve to highlight the adjustment slider for that region.

Reset adjustments in a the panel using Option key  (ALT key in PC)

Targeted Adjustment Tool

Another useful indicator  is the targeted adjustment tool.  Located on the top left corner of the Tone Curve panel, the circular icon toggles this tool on and off. Point to a spot on the photograph in the preview window and this tool  shows the corresponding spot  the Tone  Curve.  If users  click and drag the tool up and down on the image, the adjustment is centred on that region on the Tone Curve.

On  custom tone curves it moves an existing adjustment point up or down. If there is not one for that part of the tone curve it adds a new point.

This flexibility and the  ability to target specific tonal regions is one area where the Tone Curve differs from the Basic Panel.

Real Curves Tool 

Clicking on the curve icon in the bottom right corner of the Tone Curve panel changes it to a custom curve tool. This is a standard curves tool where users add and move anchor points on the curve for more control over the shape of the adjustment curve. This provides even more specific targeting of the adjustment point on the curve. The adjustment curve is superimposed over a histogram to indicate the points on the curve to adjust for a particular image.

Point curve

In Point Curve mode

Point Curve 

Click on the control icon in the bottom right corner of the panel to activate this mode. Now users can add extra control points on the curve and have full control over the amount of adjustment, crazy amounts are now possible. Point and click on a spot on the curve to add another control point.

Point and drag to move a control point along the curve. Flatten the curve with a right click of the mouse, if it all gets too messy. Hovering over a control point enables  the removal of that point, or flattening the curve.

states

The left panel is in the adjust a point state while the right is set to add a new point on the curve

Custom Curves 

In the Point Curve mode  users can create and save their own tone curves.  The default is the linear curve without any  adjustments applied to the image.  There are two other options in the Point Curve dialog, located below the curve graphic, for preset medium and strong contrast adjustment curves. These can be used as they are, or as a starting point for a new custom curve. Users save their new curve as a custom preset using the Point Curve dialog. This is a contextual dialog that adds the save option when a custom curve is created.

If you click the curves icon the Tone Curve goes back to the standard slider view and the curve is now based on your custom curve.

Colour Curves 

In the Point curve mode you can select a colour channel to adjust as well as the composite RGB channel.

Histogram

There is still the normal Lightroom histogram panel at the top of the Develop module. This is more than the normal display of  the number of pixels for the range of tones from black to  white.  There are  clipping indicators in the top corners to show when clipping occurs.

The colour of the triangle corresponds to the colour channel  that is clipping. For example, if the little triangle is yellow then yellows are being clipped, but red and blue are not. If the triangle is white then serious clipping is occurring on more than one colour channel.

The other aspect  is showing where the clipping occurs in the preview image.  To enable this feature  click on the histogram’s clipping triangle  (or keyboard  shortcut “j”). White areas that are clipping are shown as red and black areas are blue. The it is a creative decision about the importance of those areas to the photograph as a whole. Some areas of a photograph are not important. It may be better if these are clipped if it means the exposure for the main subject is optimised.

Summary 

Everything interacts and adjusting one area of the tone curve affects other areas. The Lightroom systems are designed for fast small adjustments, for complex  solutions the next step is Adobe Photoshop.  Because of the number of variables it is usually slower, but offers far greater capabilities for adjusting photographs.

Remember Lightroom is a non-destructive editor, no changes are made to the original image file, they are only applied to any exported files.

 

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