A video encoder for quantizing format-transformed source input-pictures into quantized data, and for coding the quantized data into coded bitstream, for outputting the coded bitstream, comprises a plural-density format-transformer for transforming a source input-picture into a specific format-transformed source input-picture; and a detector for detecting a variation in one of a specific luminance and color difference signal, and for selecting the specific format-transformed source input-picture for input to the quantizer depending on the variation. A decoder having a corresponding configuration is also provided.