I found a post on another board that answer this question....
Quote:
I realized that some people are creating HDRI's from pre-existing stock photo's, making multiple versions with different levels/contrasts and then re-compositing as an HDRI file.
This does not make an HDRI! It defeats the purpose.
The purpose of an HDRI is to have a complete and detailed spectrum of color and light information for EVERY detail in an image.
This creates a realistic light spectrum in 3D applications and gives hyper realistic details to photography.
To do this you NEED to take mutlibracketed photo's of the same scene from under exposed to over exposed and a few steps in between.
Without this method HDRI files will not have a full range of light and color information.
So essentially, you CAN NOT make a true HDRI from a stock photo unless you have multiple exposure brackets of that same photo.
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