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dhpdigital

Skydome Images

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    This doesn't work because most cameras capture a limited tonal range of 8 bits, which is less than we see with our own eyes. If you simply lighten this image to try to see more detail in the shadow areas you don't magically create this extra detail, which is where the merging of exposures comes in. I shoot a 3 way bracket, normal exposure, -2 stops, and +2 stops. When merged into a 32 bit file you can slide the exposure up and down a see the light and dark tones that in the 8bit file you cant.

    I hope this helps. wink.gif

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    Guest Tony Lansbury

    dhpdigital,

    Thanks for your quick reply. Yes, I see that there is a limited tonal range on an 8-bit image, but since the combined set of images are going to be used for environmental lighting only, wouldn't they (sorry, it) have enough range? (Probably talking out of my hat here!)

    I think I'm on the wrong track here, and know that you are right ... but just wondered why the detail was so important.

    By the way, I really envy you your Canon ... I've been Nikon for so long now, with so many lenses bought over the years, that I was loathe to switch. But what a lovely machine the Canon is!

    All the best - Tony

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    Here's an example of why you need a higher tonal range. If you use an HDRI created from only one exposure for a skydome then we know it doesn't have the tonal range of a true HDRI created from a bracketed sequence of images. So if we have 3 spheres with varying amounts of reflectivity then we would expect to see different amounts of light reflecting back at us. You only get this with the true HDRI.

    Dosch have made this pdf which explains it better than me http://www.dosch.de/e_infobase/HDRI.pdf

    The attached example is from their pdf and not me.

    Hope this spreads some light on the subject. (sorry, couldn't resist it)

    dhpdigital wink.gif

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    Here's one I just made with a fake HDRI.

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    Guest Tony Lansbury

    dhpdigital,

    To continue your pun, the light is beginnig to dawn on me (sorry). Seriously, thanks for your explanation. This tells me why a "quick and dirty" method I used some time ago using a TIFF never really worked.

    Even so, it would be good to come up with a quicker method to produce HDRIs. But, I suppose that if it's worth doing, it's worth doing well.

    Thanks again,

    All the best - Tony

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