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Sony A7R

Sony A7R File Sizes, Lossy Compression

Sony states 14 bits for its imaging chain. But this is not so for the raw files: 14 bits for 36 megapixels means a minimum file size of 36 X 14/8 = 63 megabytes (without compression). Therefore, a smaller file size implies compression of some kind.

Yet the A7R consistently produces 37.x megabyte files. The ONLY way this can happen is by lossy compression (data loss): when the maximum file size is a fixed size, only lossy compression can deliver a guaranteed size*. And that might result in subtle degradation to image quality in transitional areas (Sony’s delta compression), which is a possible explanation for the “rough” transitions in the Agapanthus example.

As shown below, Sony A7R raw files are invariably no larger than ~37.4 MB (files sizes do vary trivially due to an embedded JPEG preview). This proves that lossy compression is at work. No matter how good, lossy compression by definition must discard some meaningful data.

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Sony A7R forces all files to 8 bits of data per pixel

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