Image compression and decompression using controlled quality loss

A method for compressing an image, the method comprising:

• selecting, based on an error level definition representing maximum quantization error for compressing transform coefficients of the image, a sequence of quality control metrics defining an order solving multiple quality control metrics of the sequence of quality control metrics;
• iteratively processing a first subset of transform coefficients of the image according to the error level definition and the sequence of quality control metrics to produce first quantized transform coefficients;
• iteratively processing a second subset of transform coefficients of the image according to a modified error level and the sequence of quality control metrics to produce second quantized transform coefficients, wherein the modified error level represents a quantization error different than the maximum quantization error;
• and
• producing a compressed image based on the first quantized transform coefficients and the second quantized transform coefficients.

A method for compressing an image, the method comprising:

• quantizing first transform coefficients of the image according to an error level definition and a sequence of quality control metrics, wherein the sequence of quality control metrics is selected based on the error level definition and defines an order for applying multiple quality control metrics of the sequence of quality control metrics, and wherein the error level definition represents a first quantization error;
• quantizing second transform coefficients of the image according to a modified error level and the sequence of quality control metrics, wherein the modified error level represents a second quantization error different from the first quantization error;
• and
• producing compressed image data using the quantized first transform coefficients and the quantized second transform coefficients.