How is identify image signature computed in v7 ?

[starfry]

I have some code that computes an image signature like this

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$ stream -map rgb -storage-type short file.tif - | sha256sum
bf186e203ad5e7642483d0616793c2d9697629e039acbd733cc37a298eb547b8  -

It gave me the same result as `identify` when I use IM 6.9.9-35:

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identify -verbose raw.tif | grep -i signature
    signature: bf186e203ad5e7642483d0616793c2d9697629e039acbd733cc37a298eb547b8

However, when I use IM 7.0.7-23 the signature is different (the stream output is the same).

I can see that the algorthm has changed in v7 and has done before. But how is the signature now computed - can I obtain the same output with 'stream' like before ?