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Contrast can be changed by modifying the camera settings.
The icons on the exposure mode dial of your camera may adjust the contrast for the subject matter.
For example, the head icon, for portraits, may have reduced contrast.
The landscape icon may increase contrast, to make the color richer.
You can change the tone curves on your camera.
Check the instructions, and go to the menu to make changes depending on the lighting and subject matter.
You can also change the contrast with Photoshop or Photoshop Elements by changing the levels or curves.
If you saved the photograph as a raw file, the contrast can be modified when you "develop" the raw file.
The Recovery slider acts on highlight areas.
The Fill Light slider affects the shadows.
You can also develop a raw file twice.
Develop it once to optimize the highlights.
Develop the raw file again to optimize the shadows.
Then, combine the best portions of the two images into a single photograph.