Digital Camera Master

SETTING COMPRESSION LEVEL

If you chose the .jpg format in the previous post, you may want to check to see whether your camera allows you to choose different compression levels. A moderate amount of JPEG compression can dramatically reduce file size while only slightly reducing image quality; in fact, you may not notice any image degradation at all relative to a non-compressed or .tif “raw” format. As compression level increases, file size decreases, as does image-quality to some extent. Once again, you are faced with the trade-off between file size and image-quality. On those occasions where you have limited photo storage capacity, you may want to increase the compression level so that you have room to take more photos. Otherwise, you should use a setting that applies the least amount of image compression.

SETTING ISO SENSITIVITY

In some previous poust, you learn about the trade-offs between shutter speed and f-stop. The third variable that determines the amount of light that exposes the image sensor (the equivalent counterpart to film in a film camera) is the ISO setting. In earlier days, the ISO setting was known as the ASA film speed. You could then, and you can now, still purchase film that has ISO (or ASA) ratings from 50 to 800 or even 1,600 or 3,200. The higher the ISO rating, the more sensitive the image sensor is to light. Changing the ISO sensitivity setting is like so many of the other settings on a digital camera—it offers trade-offs. Some trade-offs you may like, and some, depending on what you want to achieve, you won’t like. The lower the ISO sensitivity (50 or 100), the less digital noise (the equivalent to “grain” when using a film camera) you will have. As the ISO rating goes up, your photos will have more digital noise.

You can make a decision on what ISO setting to use by asking yourself four questions:

• Do you want to avoid having digital noise in your photo, or might it be considered a “feature” of your photo?
• Does your scene or subject have enough light to use a low ISO setting?
• How much digital noise does your digital camera create at different ISO settings?
• Can you stop movement in the image and shoot without camera movement to avoid blurring the image, or is an intentional blur with a lower ISO setting something that you want?

Before making a final decision on which ISO settings are too “grainy” for your photos, shoot a few shots with different ISO settings and compare them yourself. After you’ve answered these questions, you will know what ISO setting to use.