DPR's DR test plot - JPEG - why 'S' shaped?

Started 11 months ago | Questions thread
OP xpatUSA Forum Pro • Posts: 22,220
Re: DPR's DR test plot - JPEG - why 'S' shaped?

Ellis Vener wrote:

Hi, the last time that article appears to have been updated was 2006 and it only applies to JPEGs with the camera’s “standard” processing “style” processing.


Although I did not see it mentioned, I think it is safe to assume that the sRGB color space was used. The sRGB color space has a unique tone curve which rises steeply from zero, approximating a gamma of 2.2 in the mid tones, and flattening out slightly in the highlights.

Agreed and I am familiar with the sRGB tone curve.

As to why the “S” shaped curve? It’s a close approximation to how a healthy human vision evolved: Not so well in the dark and attenuated in the bright light.

Sorry, I don't fully understand that, although I am aware of the approximate log response of the human eye. My lack of understanding stems from gamma curves not being S-shaped.

If you want a more straight line tonal response, shoot raw and output the processed results as 16-bit per channel TIFFs using the Pro Photo RGB color space.

Yes already examined with RawDigger raw channel outputs both with 2.2 gamma (can't set 1.8 in RD) and without - but thanks for the tip.

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Just interested in the technology.

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