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So I've always noticed this for years watching anime, I always look at anime characters and they seem to have to kind of milky/blurry texture on their skin/clothes. It's not to noticeable to some people, but hopefully you can see what I mean with these pictures.

(Click the pictures and zoom in for a better idea of what I mean.)

enter image description here

enter image description here

I copy and pasted the pics in Photoshop and used the eye drop tool on different areas of the skin and clothes. The color codes jump around everywhere so they can't be solid.

Could it be that these frames were scanned in at a certain DPI? Maybe something as a result of an editing software like After Effects? Or maybe it's the texture of the paper?

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    Regarding the non-solid surfaces, I would expect this is caused by the video compression, no? Even if that managed to maintain it, the conversion to jpeg surely introduced artifacts.
    – mivilar
    Commented Feb 14, 2015 at 11:32
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    The problem comes from compression. The anime is drawn at a certain resolution and then later scaled/compressed down to a lower resolution for production purposes. When this happens the larger image needs to blur/merge pixels together in order to fit the larger resolution on the smaller resolution. Pretty common issue with scaling in general. Although it's not really a problem until you get down to 480p, 720p looks fine(still noticeable), while 1080p and higher is much cleaner looking.
    – FatalSleep
    Commented Feb 14, 2015 at 12:08
  • As people have said here, it is most certainly due to the artifacts introduced by video compression. I know for a fact that in Gurren Lagann (and this probably also apply for every modern anime), they apply the color and the effects on computer, so it's very unlikely that there is any artifact at this stage.
    – nhahtdh
    Commented Feb 14, 2015 at 13:52
  • Correct me if I'm wrong, but aren't essentially all videos encoded with a lossy codec? If I remember correctly, even a one minute long losslessly encoded video can be more than a few Gigabytes big (so DVDs can't fit, and sometimes Blu-rays won't either). The problem is the compression level is set too high that the artifacts become noticeable.
    – Gao
    Commented Feb 14, 2015 at 17:08
  • @GaoWeiWei: that depends on what kind of video you're compressing. Digitally produced animes that have mostly static background images with small animated areas, lots of flat colours, and only simple panning/rotating movements can be compressed losslessly fairly efficiently from the production studios; videos ripped from a commercially produced CD/DVD/BD are typically already compressed with some lossy compression, and already contain compression artifacts even when your eyes cannot see it, so it cannot be losslessly recompressed efficiently.
    – Lie Ryan
    Commented Feb 15, 2015 at 0:30

2 Answers 2

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This happens if you encode a video with a lossy codec. In each frame the solid colors are actually drawn solid. But at the moment where they get converted into a video, a lossy compression is used. Lossy data compression discards some data from each frame so it becomes small (within the meaning of computer memory) enough to be stored on for example a DVD or so it is possible to stream them over the internet.

Compression artifacts occur in many common media such as DVDs, common computer file formats such as JPEG, MP3, or MPEG files, and some alternatives to the compact disc, such as Sony's MiniDisc format. Uncompressed media (such as on Laserdiscs, Audio CDs, and WAV files) or losslessly compressed media (such as FLAC or PNG) do not suffer from compression artifacts.

If you look close to the image you can see some kind of a square pattern (two are highlighted with circles), also called artifacts, that appears if you use lossy compression.

Artifacts

A other effect that occurs is that the color is changing. Here is a example where the left image is a lossless png file and the right image a very high compressed jpg image:

losslesslossy

The image to the left needs 168 KByte on the disc while the right only needs 2 KByte. If you want to know the reason why these artifacts are appearing, read the articles I provide below.

Information and image from Wikipedia and more information from Wikipedia.

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    Tl;dr: get the blue ray releases
    – Braiam
    Commented Feb 15, 2015 at 20:34
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So as you already know this happens due to loss of image data due to compression. This effect gets more noticeable, the lower target quality/size is for the video.

To get better screenshots, in case you don't need a particular frame of a scene, you should always go for the keyframes. In lossy video compression algos, keyframes are inserted now and then in the video stream and they contain an initial representation of a new scene, from which the fragments start moving around, so that any static fragments may not take up valuable data bits in the stream. After these fragments start moving, the image gets blurry, you start seeing artifacts, etc. Some players and most video editing apps show you when you've paused at a keyframe.

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