Blooming
Pixels on a DSLR sensor collect photons, which are converted into an electrical charge. However, the pixels occasionally collect too many photons, which causes an overflow of electrical charge. This overflow can spill onto existing pixels, causing overexposure in areas of an image. This is known as blooming. Most modern DSLRs have anti-blooming gates that help drain away this excess charge.
Chromatic Aberration
Chromatic aberration occurs most frequently in images shot with a wide-angle lens; it’s visible as color fringing around high-contrast edges. It is caused by the lens not focusing wavelengths of light onto the exact same focal plane. You might not see it on the LCD screen, but you will during editing. Typically, it’s a red or cyan outline along a subject’s edges. To prevent this, use lenses with two or more pieces of glass with different refractive qualities.
‘Jaggies’ or Aliasing
This refers to the visible jagged edges on diagonal lines in a digital image. Pixels are square (not round), and because a diagonal line consists of square pixels, aliasing can look like stair steps when the pixels are large. Jaggies disappear with higher-resolution cameras because the pixels are smaller. DSLRs have built-in anti-aliasing abilities because they read information from both sides of an edge, thus softening the lines. Sharpening in post-production increases the visibility of jaggies, which is why many sharpening filters contain an anti-alias scale. Avoid adding too much anti-aliasing; it can diminish image quality.
JPEG Compression
JPEG is the most common photo file format, despite the tradeoff between image quality and size. When you save a file as a JPEG, you compress the image and lose a little quality. If you plan to make a lot of changes to an image, save it initially in an uncompressed format, such as PSD or TIFF.
Moire
When an image contains repetitive areas of high frequency, these details can exceed the resolution of the camera. This causes moire, which looks like wavy colored lines on the image. Moire is usually not a factor with high-resolution cameras. If yours has a lower pixel count, you can use anti-aliasing filters to correct moire, although they do soften the image.
Noise
Noise shows up on images as unwanted or stray color specks, most often caused by raising the ISO. It’s most apparent in the shadows and blacks of an image, often as small dots of red, green, and blue. To reduce noise, use a lower ISO. This will sacrifice speed and is the primary reason for going only as high as absolutely necessary when choosing the ISO.
