HDRI Handbook Sample Tutorial

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Chapter 5: HDR Image Processing

HDR Image Processing

“Being ‘undigital’ with digital images”—that was the title of one of the very first papers on HDRI, written in 1995 by the visionaries Mann and Picard. And that is what it’s all about. Working directly in floating-point space is bringing image editing back home to a world where you think in f-stops, gradient ND filters, and adding light or taking it away, without ever being worried about digitally degrading your image into pixel mush. Believe me, once you have tasted the full sweetness of HDRI, you won’t ever want to go back.

5.1. Taking Advantage of the Full Dynamic Range The techniques I am about to show are all derived from digital compositing. Just a couple of years ago, ridiculously expensive movie production suites were the only systems capable of working in floating-point precision. That, and the fact that they lift all the weight of 32 bits in real time, was their major selling point. Nowadays, every off-the-shelf compositing package has the same capabilities, albeit not the speed. So these techniques work in After Effects, Fusion, Combustion, you name it. However, I’ll demonstrate them in Photoshop. Why? Because I can. The new layer and painting capabilities in CS3 Extended allow me to do so. You’ve already seen how selective exposure adjustment works. I called it the human tone-mapping operator. Well, that was just a fraction of where this can go.

This chapter is not about tone mapping. Or better said, it’s about not to tonemap the HDR image yet. We will have a look at image editing in floating-point space.

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5.1.1. Blocking Light: Day for Night This is a good one—feel free to work along starting with the Egyptian.exr from the DVD. We’re going to apply some movie magic to this image, just as professional matte painters do on a daily basis. We will change the image into a night shot. Sunlight to moonlight e We start out the very same way it would be done if we were working with a camera: We put a blue filter in front of the lens. In digital terms, that would be a new solid layer with a dark blue color. The color is chosen according to what I feel the darkest shadows should look like.

r Next, we set the blending mode of the layer to Multiply. That makes this layer the direct equivalent of a filter in front of the lens. It blocks out light, in this case a lot of it. A very brutal filter it is, indeed. But don’t panic, it’s all still in there. We just have to adjust the exposure of Photoshop’s virtual camera, just as we would do with a real photo

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HDRI Handbook Sample Tutorial by Christian.Bloch - Issuu