1. A system comprising: one or more processors; storage media; and one or more programs stored in the storage media and configured for execution by the one or more processors, the one or more programs comprising instructions configured for: obtaining compressed image data that is a coded representation of a digital image; decoding the compressed image data to obtain at least one block of discrete cosine transform (DCT) coefficients representing a sample block of the digital image, the block of DCT coefficients comprising a DC coefficient and a plurality of AC coefficients; determining probability estimates for binary symbols of binarized representations of the plurality of AC coefficients based, at least in part, on classifying each AC coefficient of the plurality of AC coefficients as being part of at most one of: (a) a top-edge row of AC coefficients of the block of DCT coefficients, (b) a left-edge column of AC coefficients of the block of DCT coefficients, or (c) a sub-block of AC coefficients of the block of DCT coefficients; arithmetic coding the binary symbols based, at least in part, on the probability estimates; and based, at least in part, on the arithmetic coding, storing further compressed image data that is a coded representation of the digital image, the further compressed image data being lossless with respect to the compressed image data, the further compressed image data requiring fewer bytes to store in storage media than required by the compressed image data.