Methods and encoders and decoders for adaptively quantizing transform domain coefficients in image and/or video encoding/decoding. For an image having a number of blocks, each block having N coefficients, the quantization step size for each coefficient is selected dynamically, thus resulting in a quantizer that may apply different step sizes to different coefficients. The selected step sizes for each coefficient are used for those coefficients within all blocks in the image/frame. In one aspect, the step sizes are selected on the basis of balancing pixel domain distortion when the image/frame is decoded.