A system adjusts the quantization parameter used to encode an image sample (e.g., pixel component). The system accesses a quantization parameter for encoding a current image pixel from an implicit rate control and obtains a measure of another image sample within a particular distance from the sample. When the measure meets a predetermined criterion, the system adjusts the quantization parameter, encodes the pixel after adjusting the quantization parameter, and explicitly indicates the adjusting of the quantization parameter to a decoding system.