141. Improve a Nighttime Photo Before You Begin  136 About an Images Histogram
See Also  138 Improve a Dull, Flat Photo
140 Lighten or Darken Part of an Image
Nighttime photography is a particular challenge. When there's not much light to work with, even the best photographers sometimes misjudge the exposure. The perennial problem with photographing a scene at night is that there's never enough natural light to produce a proper exposure. Increasing the exposure time often ruins the picture's clarity, and using a flash generally bleaches out the colors of nearby subjects while drowning out background items in the distance. In most nighttime photographs, however, the detail is therehidden, dormantand can be rediscovered not so much by increasing contrast but instead by compounding the saturation levels. The technique demonstrated here borrows a trick from the Overlay blend mode, using white as a signal to turn up the color volume. 1. | Create a Duplicate Overlay Layer
Open the image you want to adjust in the Editor in Standard Edit mode and save it in Photoshop (*.psd) format. To display the Histogram palette if it is not already showing, select Window, Histogram. From the Channel list, choose Luminosity.
TIP  | The purpose of the gradient map is to provide the Editor with a roadmap of how the transitions between darks and lights in an image should occur. Because the Foreground to Background gradient runs from pure black to pure white, the Editor doesn't apply any colorization to the pixels that are adjusted by the adjustment layer. Instead, it reprograms the midtones of the image so that they're 50% as bright as the brightest tonesjust like the gradient itself. |
With the Background layer chosen in the Layers palette, from the menu bar, select Layer, Duplicate Layer. Name this new layer Subject. Click OK.
| 2. | Create a Gradient Adjustment Layer
In the Toolbox, set the foreground color to white and the background color to black. With the Subject layer still active, select Layer, New Adjustment Layer, Gradient Map from the menu bar. Name this new layer White Shadow. Set its Mode to Overlay, and its Opacity to 100%. (It's a good guess to start out with.) Click OK.
In the Gradient Map dialog box, click the down arrow next to the Gradient Used for Grayscale Mapping strip, and choose Foreground to Background from the list of samples. Click OK.
 To reduce the number of layers down to one, from the menu bar, select Layer, Flatten Image.
| 3. | View the Result
When you're satisfied with the result, make any other changes you want and save the PSD file. Then resave the result in JPEG or TIFF format, leaving your PSD image with its layers intact so that you can return at a later time to make new adjustments.
This was a quick snapshot taken after sundown, outside the McCormick Place Convention Center in Chicago. With the original image, it was difficult to discern what you were looking atthe outside of a building or a passing spaceship. Now you can easily identify the building's entrance and unloading area.
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