An additional layer that magnifies part of the illustration, usually a character. It's a common technique used for backgrounds in character art.
If there are small differences, such as the colors being muted, partially transparent, or in greyscale, the layer having simple transforms (such as being mirrored, scaled, or rotated), or the character having a different facial expression, then it's also a different zoom layer.
If the layer is not a copy of the base image, such as featuring a totally different perspective, pose, attire, or other characters, it's a projected inset instead.
For the "zoom layer" effect used on stages by projecting the performance on background screens, use screen zoom instead.
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