Diagnosing Quality Problems

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When I use the term picture quality, I'm not talking about the composition, exposure, or other traditional characteristics of a photograph. Instead, I'm referring to how finely the image is rendered in the digital sense.

Figure 3-1 illustrates the concept: The first example is a high-quality image, with clear details and smooth color transitions. The other examples show five common digital-image defects.

High quality Pixelation JPEG artifacts

High quality Pixelation JPEG artifacts

Noise
Color cast Lense/sensor dirt
Figure 3-1: Refer to this symptom guide to determine the cause of poor image quality.

Each of these defects is related to a different issue, and only two are affected by the Quality setting on Shooting Menu 1. So if you aren't happy with your image quality, first compare your photos to those in the figure to properly diagnose the problem. Then try these remedies:

1 Pixelation: When an image doesn't have enough pixels (the colored tiles used to create digital images), details aren't clear, and curved and diagonal lines appear jagged. The fix is to increase image resolution, which you do via the Quality control. See the upcoming section, "Considering Resolution: Large, Medium, or Small?" for details.

1 JPEG artifacts: The "parquet tile" texture and random color defects that mar the third image in Figure 3-1 can occur in photos captured in the JPEG (jay-peg) file format, which is why these flaws are referred to as JPEG artifacts. This defect is also related to the Quality setting; see "Understanding File Type (JPEG or Raw)" to find out more.

1 Noise: This defect gives your image a speckled look, as shown in the lower-left example in Figure 3-1. Noise is most often related to a very long exposure time (that is, a very slow shutter speed) or to an exposure control called ISO, which you can explore in Chapter 5. To adjust shutter speed or ISO, you must switch to one of the advanced exposure modes (P, Tv, Av, M, or A-DEP).

1 Color cast: If your colors are seriously out of whack, as shown in the lower-middle example in the figure, try adjusting the camera's white balance setting. Chapter 6 covers this control and other color issues. Note, though, that you also must use an advanced exposure mode to adjust white balance.

1 Lens/sensor dirt: A dirty lens is the first possible cause of the kind of defects you see in the last example in the figure. If cleaning your lens doesn't solve the problem, dust or dirt may have made its way onto the camera's image sensor. See the sidebar "Maintaining a pristine view," elsewhere in this chapter, for information on safe lens and sensor cleaning.

When diagnosing image problems, you may want to open the photos in your photo software and zoom in for a close-up inspection. Some defects, especially pixelation and JPEG artifacts, have a similar appearance until you see them at a magnified view.

I should also tell you that I used a little digital enhancement to exaggerate the flaws in my example images to make the symptoms easier to see. With the exception of an unwanted color cast or a big blob of lens or sensor dirt, these defects may not even be noticeable unless you print or view your image at a very large size. And the subject matter of your image may camouflage some flaws; most people probably wouldn't detect a little JPEG artifacting in a photograph of a densely wooded forest, for example.

In other words, don't consider Figure 3-1 as an indication that your Canon is suspect in the image quality department. First, any digital camera can produce these defects under the right circumstances. Second, by following the guidelines in this chapter and the others mentioned in the preceding list, you can resolve any quality issues that you may encounter.

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100 Photography Tips

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