Diagnosing Picture Quality Problems with a Canon EOS 70D

By Julie Adair King

The Image Quality setting on your Canon EOS 70D determines two important aspects of your pictures: resolution, or pixel count; and file format, which refers to the type of computer file the camera uses to store your picture data. Resolution and file format play a role in the quality of your photos, so selecting the right Image Quality option is an important decision.

When the term picture quality is used, it’s not referring to the composition, exposure, or other traditional characteristics of a photograph. Instead, it’s referring to how finely the image is rendered in the digital sense.

The following figure 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.

Refer to this symptom guide to determine the cause of poor image quality.
Refer to this symptom guide to determine the cause of poor image quality.

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

  • 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 Image Quality setting.

  • JPEG artifacts: The “parquet tile” texture and random color defects that mar the third image in the figure 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 Image Quality setting.

  • Noise: This defect gives your image a speckled look, as shown in the lower-left example in the figure. Noise is caused by a high ISO setting or by a long exposure time.

  • Color cast: If colors are out of whack, as shown in the lower-middle example in the figure, try adjusting the camera’s White Balance setting.

  • 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.

    Your camera has an internal sensor-cleaning mechanism that runs every time you turn the camera on or off. You also can request a cleaning session at any time via the Sensor Cleaning option on Setup Menu 4. If that proves inadequate, a manual sensor cleaning is necessary.

    You can do this job yourself, but it’s not recommended because you can easily damage your camera if you aren’t careful. Instead, find a local camera store that offers this service. Sensor cleaning typically costs about $50, but some places offer the service for free if you bought the camera there.

It should be stressed that some image-processing liberties were exaggerated to create the flaws in the 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.