I think it's known as color banding or contouring. Also called Posterization sometimes.
What are common digital artifacts?
Aliasing: Aliasing refers to the jagged appearance of diagonal or curved lines due to the square nature of pixels. Aliasing is mostly a problem with files sizes which are too small, and when a photo is interpolated beyond Veer's standards
Artifacts: Artifacts are undesired effects to an image caused by the camera's sensor, lens, and environmental variables. These include: blooming, chromatic aberrations, jaggies, maze artifacts, moiré, ISO noise, and mottles.
Banding: Please see Posterization.
Blocking: Blocking is an artifact which is usually a result of a data compression algorithm or resampling an image too large. The artifacts appear as large block of grouped pixels.
Blooming: Please see Chromatic Aberration.
Color Cast: the effect of one of the color channels dominates the overall tone or hue of the photo. Usually caused by improper exposure, improper white balance setting and/or unusual lighting conditions when shooting the original image.
Cast: cast is the effect of one color dominating the overall look of an image and cause an overall shift in color. These shifts can affect the colors of the highlights and shadows and cause an unnatural appearance.
Chromatic Aberration: Chromatic aberration or blooming is caused by light rays of different wavelengths coming to focus at different distances from the lens. Aberrations are seen as color fringes or halos along edges and around every point in
Clipped Highlights: Highlights are the lightest significant part
of an image. When a highlight is clipped, there is a loss of details which cannot be recovered.
Color Fringing: please see chromatic aberration.
Filled Shadows: Shadows are the darkest significant part of an image. When a shadow is filled, there is a loss of details which cannot be recovered.
Fringing: please see chromatic aberration.
Interpolation: Interpolation or resampling is an method to increase (or decrease) the number of pixels in a digital image. Photo applications use algorithms to enlarge the photo while minimizing the aliasing or jaggies.
ISO noise: please see Sensitivity (ISO).
Lens Flare: Lens flare occurs when an image includes a very bright light source, flare generated by a bright region can have enough intensity to become very visible. The light produced by flare mechanisms superimposes broadly across the image, adding light to dark image regions and reducing image contrast. This effect can be desired or not. Software can sometimes minimize or remove lens flare, depending on the severity of the lens flare.
Jaggies: Jaggies is a non-technical, and more descriptive, name for aliasing. Please see Aliasing.
Maze Artifacts: maze artifact is a wavy moiré pattern that begins to resemble a maze, usually observed in JPEGs.
Moiré: Moiré patterns are undesired artifacts of images. Optical patterns of lines can create a real and visible pattern of roughly horizontal dark and light bands superimposed on the lines: this is a moiré pattern.
Mottle: Mottle is an artifact that appears as spots or blotches of different color or shades of color within a continuous tone.
Noise: Noise in digital images is most visible in uniform surfaces, and is similar to grain that we see in film. Noise increases with sensitivity, especially the color noise in digital cameras. Higher sensitivity (ISO) increases the chances of noise, but the environment is also a factor. Please see Sensitivity (ISO).
Posterization: Posterization is an artifact which occurs when a limited number of tones are forced to cover a longer range than intended. This causes visible banding or posterization, which are very noticeable in smooth gradients such as skies.
Resampling: please see Interpolation.
Resolution: Refers to the sharpness and clarity of an image. This is why Veer has set standards on file size, to insure optimal image quality.
Sensitivity (ISO): Digital cameras set the level of sensitivity to light by the ISO settings on the camera. Increasing the sensitivity, requires less light. ISO noise is most common in the shadows or areas of continous tone. Software filters can sometimes minimize the noise, but sometimes the noise is beyond repair.
Sensor Dust: Dust has always been a concern for photographers, and digital photography is no different. A dust particle on a digital SLR sensor will show up in every photo, appearing a as black smudge or spot. These spots created can usually by addressed using Photoshop, but it can be time-consuming since the spots will continue to appear in each and every image. Photographers will need to periodically maintain their equipment to ensure the sensor is clear of dust and debris.
White Balance: The perceived color of an object is affected by the color of the lighting under which it is viewed. The human brain is able to detect and compensate for such changes in perceived color. As a result, a white object will look white to humans whether viewed in sunlight or under overcast skies, or indoors. The color balance assumes that under normal conditions, that if a white object can be made to look white, then the remaining colors will be accurate too.