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Take your photo back in time with a gradient map

Added on Thursday 26th of November 2009 01:51 am EST
 

Application:

Adobe Photoshop CS/CS2/CS3/CS4

Operating Systems:

Macintosh, Microsoft Windows

 

Though many times you may have the option of photographing at the time of day you want, there are times when you can’t. In these cases, Photoshop offers a unique solution—use a gradient map to alter the image’s colors, thus appearing to change the time of day.

 

To change the time of day in a photograph, we’ll:

     Explain how gradient maps work.

     Explore how the sun’s location affects an image’s color temperature.

     Create and apply a custom gradient map adjustment layer to an image.

 

When shooting a photo, not only is the choice of subject important to the composition, but the time of day you shoot plays an important role as well. A photo taken at 8:00 a.m. doesn’t quite convey the same early morning quality of the same subject taken even an hour or two later. Many factors contribute to this change, such as angle of the sun, temperature of the air, and color temperature of the lighting source. While perhaps nothing but some serious photo editing can change the angle of the sun, you can easily change a more dominant factor—the time of day—as we did in Figure A. To do so, we’ll use a Photoshop feature that might surprise you—a gradient map.

 

A

 

How gradient maps work

A gradient map is a gradient that Photoshop applies (maps) to an image based on the image’s tonality (its highlights, mid tones, and shadow areas). Photoshop maps the colors in a gradient from right to left, highlight to shadows. If, for example, you were to apply a gradient map that progresses from green to red, as shown in Figure B, the image highlights would appear green, the shadows would be red, and the mid tones would be the shades in between, as shown in Figure C.

B

 

C

 

Photoshop enables you to apply a gradient map to an image in one of two ways. You can apply it directly to the image itself, or you can apply it to an adjustment layer. When applied to an adjustment layer, you can edit the gradient map as well as change its blending mode, which is what we’ll do to change the apparent time of day in a scene.

 

The role of atmosphere in color temperature

As the sun rises, the shadows it creates continually grow shorter until sometime around noon when they grow longer again. You would think that a shot taken about an hour after sunrise would look very similar to one shot about an hour before sunset, except for the direction of the shadows. At times this is true, but most often, it isn’t.

 

The sun’s effect

As the sun rises, it warms the atmosphere, which in turn, changes the amount of moisture the atmosphere can hold. This, coupled with greater wind activity, increases both water vapor as well as dust particle content.

This effect results in a general shift in light source and color temperature throughout the day from warm to cool to warm again. But since the atmospheric conditions just after sunrise aren’t the same as those before sunset, the warm color temperatures experienced just after sunrise aren’t as intense as the ones experienced towards sunset. As a result, the light of early morning generally appears somewhat cooler than that of later afternoon. This difference is due more to the color temperature of the shadow areas than that of the highlight areas.

 

The atmosphere’s effect on shadow areas

Shadow areas are mostly lit by the sky (the atmosphere), which as we just mentioned, constantly changes throughout the day. So while the highlight areas do differ somewhat from early morning to late afternoon, the shadow areas differ considerably. Because you can control the appearance of highlight, mid tone, and shadow image areas via the Gradient Map Adjustment Layer command, you can adjust the apparent time of day in a photograph.

 

Open and study an example

Let’s open an example and examine the highlight, mid tones, and shadow areas to determine how we want to alter them. To follow along using our example, download the file woods.zip from the URL given at the beginning of this article. Extract the file woods.jpg, launch Photoshop, and open the file shown in