How to Avoid Artifacts in Digital Photos

Understand How to Avoid Undesirable Changes in Your Digital Photos

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Digital artifacts are any unwanted changes that occur in an image that are caused by various factors within a digital camera. The can appear in both DSLR or point and shoot cameras and cause reduce the quality of a photograph.

The great news is that by understanding the different types of image artifacts, they can (for the most part) be avoided or corrected before a picture is even taken.

Blooming

Pixels on a DSLR sensor collect photons, which are converted into an electrical charge.

However, the pixels can 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 which help to drain away this excess charge.

Chromatic Aberration

Chromatic aberration occurs most frequently when shooting with a wide-angle lens and it is 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 may not see it on the LCD screen, but it can be noticed during editing and will often be a red or cyan outline along a subject's edges.

It can be corrected by using lenses that have 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 a set of square pixels it can look like a series of stair steps when the pixels are large.

Jaggies disappear with higher resolution cameras because the pixels are smaller. DSLRs naturally contain anti-aliasing abilities, as they will read information from both sides of an edge, thus softening the lines.

Sharpening in post production will increase the visibility of jaggies and that is why many sharpening filters contain an anti-alias scale. Care should be taken to avoid adding too much anti-alias as it can also diminish image quality.

JPEG Compression

JPEG is the most common photo file format used to save digital photo files. However, JPEG gives a trade-off between image quality and image size.

Every time you save a file as a JPEG, you compress the image and lose a little quality. Likewise, each time you open and close a JPEG (even if you perform no editing on it), you still lose quality.

If you plan to make a lot of changes to an image, it's best to 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 eliminated by higher resolution cameras. Those with a lower pixel count can use anti-aliasing filters to correct the problem of moire, although they do soften the image.

Noise

Noise shows up on images as unwanted or stray color specks, and noise is most commonly caused by raising the ISO of a camera.

It will be most apparent in the shadows and blacks of an image, often as small dots of red, green, and blue.

Noise can be reduced by using a lower ISO, which will sacrifice speed and is the primary reason for only going as high as absolutely needed when choosing the ISO.