A high quality, fast inverse halftoning algorithm for error diffused halftones

We present an inverse halftoning algorithm for error diffused halftones. At each pixel, the algorithm applies a separable 7/spl times/7 FIR filter parameterized by the computed local horizontal and vertical gradients. All operations are entirely local; only 7 rows of image storage and fewer than 300 operations per pixel are required. The algorithm can be easily implemented in embedded software or hardware. We compare our algorithm with previously reported approaches, and show that it delivers comparable PSNR and subjective quality at a fraction of the computation and memory requirements. A C implementation of the algorithm is available.