Spotting Photo Quality Problems with a Nikon DSLR
Picture quality is not the composition, exposure, or other traditional characteristics of the photographs you take with your Nikon D3100, D5100 or D7000. It’s how finely the image is rendered in the digital sense.
Each of these defects is related to a different issue, and only one is affected by the Image Quality setting on your Nikon dSLR. 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:
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 Size control.
JPEG artifacts: The parquet tile texture and random color defects that mar the third image can occur in photos captured in the JPEG (jay-peg) file format, which is why these flaws are referred to as JPEG artifacts. This is the defect related to the Image Quality setting.
Noise: This defect gives your image a speckled look. Noise can occur with very long exposure times or when you choose a high ISO Sensitivity setting on your camera.
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.
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.
The D5100 and D7000 offer an automated, internal sensor-cleaning mechanism. By default, this automatic cleaning happens every time you turn the camera on or off. You also can request a cleaning session at any time via the Clean Image Sensor command on the Setup menu. But if you have a D3100 or frequently change lenses in a dirty environment, a manual sensor cleaning is necessary. Image sensors are pretty delicate beings, and you can easily damage them or other parts of your camera if you aren't careful. Instead, find a local camera store that offers this service.