iPhoto Adjustments - Exposure & Contrast
This article is part of a series where I will cover the image adjustment features of iPhoto. Many users do not make full use of the adjustments offered by iPhoto. With iPhoto 08, Apple has introduced image adjustments that were usually only previously found in professional image editing applications.
Exposure & Contrast
The exposure adjustment controls the overall lightness and darkness of the image. Similar to its meaning when taking a photo, a low exposure describes a darker image and a high exposure describes a lighter image. Even though the exposure adjustment can change the overall exposure of an image, it will not add any detail lost if the original image was either under (too dark) or over (too light) exposed. You should always be trying to take shots that are correctly exposed, ensuring that maximum detail has been captured.
The contrast adjustment changes the differences between the lightness and darkness of the image. By increasing the contrast, the lighter parts of the image become lighter and the darker parts become darker. Conversely, if you decrease the contrast, the differences between lighter and darker parts of the image decreases.
To display the image adjustments HUD (Head’s Up Display) in iPhoto, either of the following will work.
- Select a photo in the browser and click the ‘Edit’ button in the toolbar at the bottom, or
- Double click a photo in the browser and then select the ‘Edit’ button in the toolbar at the bottom
To demonstrate the effects that the Exposure & Contrast adjustments have on a photo, we will be using the following photo of the Sydney Opera House with a couple of passing Sydney Ferries. The image Adjustment HUD is shown to the right. Adjustments can be made in either windowed or full-screen mode.
The Exposure & Contrast adjustments also change the tone curve displayed, similar to the Levels adjustments detailed in the iPhoto Adjustments - Levels article.
Each color is represented in a value between 0 and 255, and are represented on the graphs scale as between 1 and 100%.
Low Exposure Adjustment
The lower exposure values can be adjusted between 0 and -3.00 in increments of approximately 0.05 (the scale is not completely linear).
As you lower the image exposure, the graph will show the image tonal detail moving to the left. This has the effect of darkening the image. As the image becomes darker, the detail is being squashed into the darker parts of the image.
High Exposure Adjustment
The higher exposure values can be adjusted between 0 and 3.00 in increments of approximately 0.05 (the scale is not completely linear).
As you increase the image exposure, the graph will show the image tonal detail moving to the right. This has the effect of lightening the image. As the image becomes lighter, the detail is being squashed into the lighter parts of the image.
Low Contrast Adjustment
The lower contrast values can be adjusted between 0 and -100 in increments of approximately 1 (the scale is not completely linear).
As you lower the contrast of the image, the image tonal detail appears to become squashed towards the center. The effect on the image is for the differences between the darker and lighter parts of the image to become closer. If you lower the contrast too far, the image starts to appear flat.
High Contrast Adjustment
The higher contrast values can be adjusted between 0 and 100 in increments of approximately 1 (the scale is not completely linear).
As you increase the contrast of the image, the image tonal detail appears to become expanded towards the ends. The effect on the image is for the differences between the darker and lighter parts of the image to become further apart. If you increase the contrast too far, the image starts to appear too unrealistic; however, this can be an effect that can add something special to certain images. In the example image, the higher contrast make the ivory colored sails of the Sydney Opera House appear more white and the water to appear a darker green. A slight increase in contrast can give an image more punch, especially if it has been taken on a bright day that can flatten out a lot of the colors.
Summary
Adjusting the exposure and contrast of an image can have dramatic effects on the overall image. Be careful to only make subtle adjustments at a time.
As with all adjustments in iPhoto, it is possible to reset the changes if you over adjust an image. If the ‘Edit’ -> ‘Undo’ option will not undo all of the changes, you can revert the image to its original using the ‘Photos’ -> ‘Revert to Original’ option. When using RAW images, the ‘Photos’ -> ‘Reprocess RAW’ option should be used.
Exposure and Contrast can be a powerful and effective way of making adjustments to your photos. In subsequent articles, I will cover the other available image adjustment features of iPhoto.
Tags: Apple iPhoto, Photo Adjustment
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Marius said,
Wrote on May 15, 2008 @ 1:26 pm
Help us with our online contrast experiment: http://www.leneogmarius.net/Contrast/