View Full Version : exposures for hdr map
11 November 2004, 09:59 AM
I found a tutorial which explains a way to create hdri map from an image, here is the link:
My question is about the way he created the different exposures in photoshop, what tools do you use in photoshop to underexpose and over expose an image properly?
As you can see I am a photoshop novice so any advice would be greatly appreciated.
11 November 2004, 10:06 PM
Re-read the third paragraph, the exposures were made in the camera, not in Photoshop.
"... I was able to shoot the different exposures by varying the aperture as, obviously, the shutter speed of a video camera is fixed. Once I had shot 6 still images of the probe at different apertures and ..."
You can't make proper HDR out of a single photo. If you took the fourth ball and tried to use Levels on it, you would never get any detail in the view out the window... it would always be washed out, it wouldn't equal the image detail you see out the window in the first ball.
Hope that helps.
11 November 2004, 10:35 PM
Eric, I've faked HDRI from a single photo with better-than-expected results. Of course, not quite as good for some things, but damn fine fakery.
Colour Dodge and Burn come in very handy for this. So does the luminosity channel and various other little things.
One of these days I'll finish writing about my fiddlings.
11 November 2004, 10:46 PM
Yeah, good to know you can fake it. I should note for Dan's sake that this is not proper HDR, because you don't get the detail in the darkest/brightest regions, but like you say a reasonable facsimile will work in many cases.
Here we do a sort of HDR fakery with our cubemaps in a real-time engine... we put a mask in the alpha channel of the cubemap, and this is used to boost/degrade the RGB pixels, giving us a 0% to 200% brightness range in our reflections, all in real-time. So when the cubemap is in the bkg it is just showing the RGB, but when it is reflected in a surface then it is multiplied/adjusted by the alpha. Gives you something like the effect you see when you look at someone's eyeball... only the brightest parts of the room are visible on the surface of their eye.
I'd like to see your writeup when you're ready.
11 November 2004, 11:10 PM
The mask trick! I thought I was the only one that did that.
Manipulating opacity is a great way to fake intensity - as I put it.
Yet another thing I've been meaning to write a tutorial about.
Yes, what you said about details.
If you are going to fake it, know the limitations.
11 November 2004, 09:33 AM
Thanks for all your help, much appreciated.
11 November 2004, 01:10 PM
Here is the first set that was my very first fiddle:
I made #2 from some space photos.
Then I made a low and a high from that.
This was my first whack at it and definitely needs work. But shows that the techniques do have potential.
Go ahead and put them together using HDRI Shop.
When you do, there is a button you need to push to adjust the points. Something like Adjust Black and White or Calculate. Yeah, Calculate sounds right. Be sure to click it after you load the images or else you'll get artifacts.
I'll get to a full-blown tutorial one of these days.
You know, proper and stuff.
01 January 2006, 07:00 PM
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