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dhpdigital

Skydome Images

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Right then, where I'm at with this project. I've spent a load of cash on the hardware, and with the software that I have I can give out a hi-res file in 8bit rgb 7000 x 3500 px. I can double that res in future if needed, but thought that it would be enough for now.

I can't produce an HDRI file yet without upgrading the software which will cost me a few hundred ££££££, so you'll have to what for that I'm afraid. I'm going to continue to shoot the sequence file for now to build up a library.

Mods please can you let me know the best way to supply the file? The DL's are max of 2mb. I can give a link to my ftp to start a DL automatically?

dhpdigital.

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I'm setting a download page so you guys here can have a nice big 7000x3500 px jpeg of these images. I'll inform you when it's ready in a new post. These are low-res versions for now so you can see what you'll be able to have. There are more shot which need to be stitched and processed to come. Also hi-res HDRI's will follow asap.

dhpdigital wink.gif

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Thanks for the info Lennart. That looks like a good application and it has a great price too. I would like to point out that it doesn't look like it actually creates .hdr 32bit files, so you wouldn't be able to use the output it makes to light your scene using GI. It would be good for the background image though as it does give you 'human eye perception to your photographs'. wink.gif

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Guest Tony Lansbury

I've always been intrigued by HDR images, and how they are created.

With the intoduction of Photoshop CS2 it became possible to use one image to create, say, 5 more with different levels. These could then be merged into a single HDR image. OK, you have to be careful with the range of levels that you use ... it is important to use a sufficient range so that, for example, the darkest image has 8 stops less exposure, say, than the lightest (just using an example here).

Why shouldn't this produce just as good a result as setting up a camera on a tripod and bracketing. Obviously something I don't know here!

I need the technical why's and wherefore's on this. Anybody help on this please?

All the best - TL

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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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