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List of all types of Image Noise and Artifacts

Russell Spears , Jun 20, 2008; 01:11 p.m.

This is a list of imaging terms I have been collecting off the web, if anyone can add to it or better help describe it it would be great. I am using my own definition of Noise and Artifacts here-it is most likely many would not like this distinction, but I find it usefull in classifying these affects.

By NOISE I mean any non-image affects that occure between the sensor chip and wrighting of the RAW file. This includes the cameras circuitry and any algorythens used to make the resulting file(s)-anything that can negatively affect the fidelity of the recording process from the moment the light is recorded to the moment the digital negative is produced.

By ARTIFACTS I mean any class of non-image changes introduced by the lenses or post-processing of the RAW file. As the term implies, the effects of these various manipulations of the RAW file can leave visible affect (artifacts) within the image information throughout the workflow.

"Purple Fringing" usually refers to a typical digital camera phenomenon that is caused by the microlenses.

"Blooming" is a type of noise where an excess of charge flow over to surrounding pixels, brightening or overexposing them in the process.

"Pixilation Noise" (jaggies/aliasing) is due to insufficient image information/resolution for the required output. This type of information loss is part of the restrictions of the CMOS chip used to record the image.

"Pixilation Artifacts" (jaggies/aliasing) is information loss idue to post-production down sampling.

"Chromatic aberration" or "color fringing" is an artifact caused by the camera lens not focusing different wavelengths of light onto the exact same focal plane.

"Maze Artifacts" are moiré patterns caused by the camera's internal image processing to generate "maze" like patterns. If this is post-processing of the RAW file in-camera, I think it should be consdered an Artifact, if it is done as part of making the RAW file it should better be described as noise.

"Moire Patterns" If a scene contains areas with repetitive detail which exceeds the resolution of the camera (1), a wavy moiré pattern can appear. This may be a type of noise, but a unique class for sure.

"Sharpening Halos" the affects of モDigital resolution" where sharpness is faked by making the edges more contrasty.

"Luminance Noise" fluctuations in luminance across different channels-monochromatic grain, similar to film.

"Color Noise" or "chromaヤ noise is not luminance noise, but I do not have a good definition here?

"Posterization" is an artifact that occurs when an image's apparent bit depth has been decreased so much that it has a visual impact. a loss of continuous tone information.

"Color fringing" is this really different than "Chromatic aberration"?

"Channel noise" is random spikes in long exposure modes.

"Barrell distortion" is the distortion of actual pixel information due to the effects of lenses without proper coating.

Random noise is characterized by intensity and color fluctuations above and below the actual image intensity. There will always be some random noise at any exposure length and it is most influenced by ISO speed. The pattern of random noise changes even if the exposure settings are identical

Fixed pattern noise includes what are called "hot pixels," which are defined as such when a pixel's intensity far surpasses that of the ambient random noise fluctuations. Fixed pattern noise generally appears in very long exposures and is exacerbated by higher temperatures.

Banding noise is highly camera-dependent, and is noise which is introduced by the camera when it reads data from the digital sensor. Banding noise is most visible at high ISO speeds and in the shadows, or when an image has been excessively brightened. Banding noise can also increase for certain white balances, depending on camera model.

"JPEG artifacts" (JPEG compression artifacts) Artifacts in digital images are unwelcome and unnatural elements or distortions.

"Interpolation Artifacts" any type of non-image information used to upsample image date.

This is all I could find, do you know of more or have better definition to use?

Responses


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Russell Spears , Jun 20, 2008; 01:41 p.m.

And sorry for not spell checking

Rob Bernhard , Jun 20, 2008; 01:50 p.m.

There's also two other failures types for pixels.

stuck pixel: a pixel that always reads out one color regardless of exposure length or ISO and

dead pixel: a pixel that never reads out any information (always is black)

[["Barrell distortion" is the distortion of actual pixel information due to the effects of lenses without proper coating. ]]

Barrel distortion doesn't have anything to do with lens coatings. It has to do with lens design.

Russell Spears , Jun 20, 2008; 01:54 p.m.

Thanks Rob... Did you find the Noise/Artifact distinction useful?

Rob Bernhard , Jun 20, 2008; 01:59 p.m.

I think it's a good idea to have a list like this for reference. With a little more work (perhaps some examples and clarifications, where needed) this would make for a good addition to the Learn section of photo.net

Russell Spears , Jun 20, 2008; 02:01 p.m.

Could Color noise be an example of a stuck pixel as you describe it?

David W. Griffin , Jun 20, 2008; 02:30 p.m.

Note that Apochromatic lenses (APO) are designed to minimize Chromatic Aberration. Even in the black and white days, an APO lens could make a picture look sharper because failure to focus different frequencies of light to the same point caused things to look a touch out of focus.

Thetis Kamares , Jun 21, 2008; 05:41 p.m.

I think it would be good to separate the list into optical and media/film/camera artifacts before it gets any longer.

To that end, the six basic optical aberrations (some of which you mention - and good catch on distortion, Rob) are:

1. chromatic aberration - color fringing caused by focal length varying according to color (wavelength) of light; combated by using optical materials with various refractive indices

2. spherical aberration - blur of point images caused by focal length varying at different distances off-axis; that is, the lens doesn't have the same FL at the center and edge of the optics (not the image); perfectly spherical optical surfaces cause this defect but are easiest to manufacture

3. coma - radial blurring increasing off-axis; related to spherical aberration

4. astigmatism - caused by cylindrical asymmetry ("lopsidedness") in the optics (the optics are therefore not radially symmetric; contrast with spherical aberration)

5. distortion - focal length (magnification) varies radially across the image (contrast with spherical aberration)
5.1. barrel distortion - FL increases toward center of image
5.2. pincushion distortion - FL increases toward edge

6. field curvature - the focal surface is not a plane, leading to best focus in the image center or in a ring around the center; some specialty cameras (e.g. Schmidt cameras) incorporate curved film or plate holders

Russell Spears , Jun 22, 2008; 10:09 a.m.

What I have found in many of the posts on the web and in many "top" books, is a lack of consistent language over some important imaging issues-this is just a great conversation to have!

Now, if your thinking of dividing the class of Artifacts into a sub groups I think it makes good since because the Artifacts list did not seem to fit nicely into one single exhaustive class of its own, but do you think the noise class of affects are clear enough given that it is describing the narrow group of affects relating to imaging ability of the sensor chip to the output of a digital negative. The whole class would describe, well, the range of the sensor's fidelity-if it changes of not, and the quality of the circuitry/software producing the RAW file.

Bill Tuthill , Jun 22, 2008; 05:38 p.m.

Nice list!

Chroma noise is when you have bogus RGB pixels in dark areas, rather then uneven white/gray/black. Film shows chroma noise, especially expired 800 speed film.

Color fringing is a superset of purple fringing. Telephoto lenses often show green or blue on one side of objects and purple or red on the other. I'm not sure why digital cameras suffer primarily from purple fringing in the corners, and not other colors.


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