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Pancho
08-31-2006, 03:24 PM
Hi everybody,

I don't have to much experience if it comes up to matching different image material, but I do have an approach which might be interesting for everybody, if it's not already some kind of standard. I'm mainly using Lightwave 3D for creating images which I need to match with footage from a Nikon D2X. My idea is:

Creating a series of images from a gray card with a certain difference in f-stops with the Nikon. e.g. one f-stop steps or 1/3 f-stop steps, from pure white to deepest black. So far I'm using this as a visual reference, but I'd like to transform it into some kind of camera response curve, so that it is my master curve I need to match afterwards.

In Lightwave I would do the same by changing the lighting intensity in the same manner, rendering a series of image with the same f-stop steps. What I would need to do know is match the grayscale from the 3D app with the grayscale from the Nikon.

Is there a way to create a curve I could use on .hdr files from Lightwave, so that they look more or less the same like images taken with the Nikon? So far I'm just think of the gradation, but if there is a way to match the colors too, I would be pretty glad. Cinepaint is supposed to be able to work nicely with HDR images, but I don't know which image sizes it can handle, as I'm a photographer and not a movie maker.

I hope I could point out what I want to achive. Anyone has an idea which way I would need to follow to reach what I'm aiming for? In the end I would like to load my 3d images into an application, load a preset which changes the gradation and colors and then save the hdr file to a 16bit TIF or other 16bit image format, so that I can do the compositing in PS or some other program.

Cheers and thanks in advance
Pancho
danylyon
09-04-2006, 04:40 PM
Yes I think we're triing something similar ;)

The thing that won't work is, color correcting the HDRI Image. Then you throw off your lightning. Imagine you'd darken the midtones, while Color correcting, this would mean there comes less light in the midtones, which wouldn't result in less light in the midtones in the final 3D rendered image. (at least that's how my head would think ;-)
The HDRI Map, has to be in a linear Colorspace.. which I think it IS after you've put it together in HDR Shop or Photoshop. But not too sure about it. (But then again, there can't be any Gamma corrected HDRI images, because Gamma only works between 0 and 1?!)

Then.. you're 3D Images come out linear aswell, meaning, they should look "to dark" on your Gamma 2.5 PC Monitor.

Then in photoshop, you'd apply a Gamma 2.5 color correction to the 3D Footage and it should match pretty well.
(I think Digital Cameras work in Linear Color Space, but Photoshop applies an sRGB curve)

Ok.. most of what I just said should maybe more be understood as a question.. I'm not too sure about all that.
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