From Angel Island by PicMax

I took this photo last year during a hike to the summit of Mount Livemore on Angel Island, San Francisco. It was a great hike but obviously the photo looks dull and unattractive. It was slightly hazy that day and the camera, Nikon D70, didn’t do the magic for me. No problem. Let me show you how to fix photos like this one using Nikon Capture NX in several different ways.

Before we start

Let’s look at the histogram of this photo first. The luminosity histogram is a representation of total number of pixels (the vertical-axis) at different luminosity levels (horizontal-axis). The left side of the histogram represents the darkest tones in your image, while the right side represents the lightest tones in the image.

From the histogram of the photo, it is quite obvious why the photo looks so dull. The range of the luminosity values of the scene is very narrow so it does not contain shadows that are dark enough and high lights that are bright enough, which causes the overall lack of contrast in this photo.

Method 1: Brightness and Contrast

This is probably the easiest. You can simply open up the Brightness & Contrast adjustment (Adjust->Light->Contrast/Brightness…) and drag the separate brightness and contrast sliders around while you are watching the image. You can stop when you are satisfied with the result.

This method is quite subjective even though it can work well enough for most people. To include some practical guidance in the adjustments, you can watch the histogram window. What you would like to do is to expand and shift the tone distributions to fill the entire window of the histogram. Dragging the contrast slider to the right will widen the tone range while dragging to the left will do the opposite. The brightness slider will shift the entire histogram to left and right while the shapes of the distributions will remain unchanged. The following chart illustrates the effects of the brightness and contrast adjustments.

When you make adjustments, watch out the left and right boundaries of the histogram window. The boundaries represent the darkest shadows (left) and brightest highlight (right) of the image. When the histogram is partially clipped by either boundaries, the image details will be lost, either as completely black patches or as blown highlights depending on which boundary clips the histogram. To maximize the contrast without losing image details, simply shift (use brightness slider) and  fit (use the contrast slider) the histogram to fill the entire window.

Please note this is only a guide not a rule. Sometimes it is perfectly OK to lose some non-essential details from the images in order to achieve desired results. And the opposite, not having true black and white points in the photo, is also acceptable in many cases.

For the example photo, I find the brightness of -9 and contrast of 70 looks pleasing to me as shown in the following screen capture.

Method 2: Level and Curve

The second method is more straightforward than the first one. Open the Levels & Curves adjustment via Adjust->Light->Levels & Curves… or hit Ctrl-L.

First, drag the black point slider towards the center. The image luminosity values from that point and all the way to the left will be set to completely black. Capture NX will then stretch and redistribute  the available luminosity values to match the entire possible range of values. This stretching will not be shown in the histogram embedded in Levels & Curves dialog box but will show up in the histogram in the photo info window (Open it by going to Window->Photo info). What we want to do is to move the slider to the left-most point of the histogram so the shadow areas are dark enough.

Second, drag the white point slider towards the center to the right-most point of the histogram. This will set the white point of the image so the highlight areas of the image will become brighter. The following two screen captures illustrate the above steps.

Finally, we can adjust the midpoint slider to the left or the right to brighten or darken the mid-tones of the image. For the purpose of enhancing the contrast, I found a S-curve adjustment will work out better.

Below is the final result and its histogram.

Method 3: High pass

I previously showed you how to use high pass for sharpening purpose in Capture NX. For sharpening, we need a small radius of a few pixels in the setting. If we use a larger radius, we can achieve contrast enhancement that is confined to certain areas of the photo with edge details having characteristic sizes defined by the radius you set in the high pass setting. The advantage of this method is that it will not affect  other areas, such as skies and waters that have larger than the set radius edge details. This is an advantage but sometimes it is also a limitation because it may not get you the desired overall contrast. Consider the other methods as global contrast enhancements and high pass a local contrast enhancement method. You may need to use this method combined with one of the other two methods above to achieve the desired over all results.

Hopefully this does not sound too confusing to you. To demonstrate how high pass contrast enhancement works, I will start with the resulting photo of from the 2nd method above. Access the high pass command by going to Adjust->Focus->High Pass… as shown below.

Once selected, you will see the image turn into something almost completely gray and the high pass settings dialog box will pop up.

The default radius setting is 1. Drag the radius slider to right and you will see more and more original photo details go through the gray background. Since it is in the default blending mode we are not able to judge the effect easily. Simply click OK to continue.

Go to the Edit List (Windows->Edit List if it is not already open) and open the opacity options dialog box of the High Pass edit step. Change the settings to something like the following.

Click OK then go back to the high pass settings dialog box and move the radius slider around until you are satisfied with the result. There is really no fixed value that is good for all situations. Best value for the radius will depend on the details and size of the image. If the radius is too large, some halo effect may be observed around parts of the image. Simply reduce the radius until the halo disappears.

Go back to opacity options and lower the opacity if the effect is too strong. You may need to zoom in to view the effect more clearly since the changes are confined to localized areas.

The screen capture below shows the result of the high pass adjustment.

It is difficult to appreciate the effect of the high pass from small images shown above. So here are some 100% crops from all three methods used above: Brightness&Contrast (top), Levels&Curves (middle), and Levels&Curves + High Pass (bottom).

The 100%-crop image with the high pass edit step does seem to have extra contrast but shouldn’t we be able to achieve it with the other two methods?

Yes and No. At any given areas of the photo, it is possible to obtain something similar with all three methods. However, if you want to only enhance contrasts of details with certain spatial characteristics (size of the edges), high pass is an effective choice. Brightness&Contrast, and Levels&Curves adjustments operate on the entire image data without discrimination of the spatial characteristics. In the high pass example here, the trees are visibly darker compared to the 100%-crops produced from the Levels&Curves adjustment but the sea surface is not significantly darkened. If you still remember, we applied the high pass on top of the Levels&Curves adjustments.

The final words

I hope you enjoy reading this tutorial on contrast enhancement in Nikon Capture NX. Please feel free to let me know if you have any comments or suggestions. If you are interested in other Nikon Capture NX tutorials, you can find more by following this link.