Official BeyondUnreal Photography Thread

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L

lkaven

Guest
Indeed, thanks a lot Luke! When I have some free time to spare I'm definitely going to try executing the technique you've explained. :)

Just one more question, if you don't mind sharing with us, what exactly does the merging of multiple HDR images achieve better than tone-mapping from a single one - what are the perks?

First to untangle terminology a bit. A single shot exposure is a low dynamic range image (LDR), something that typically has 8-10 stops of usable dynamic range in it. With a good photon counter like the D3, you can get surprisingly clean capture right down to the lowest bit, so there is quite a bit of detail in the shadows of a very good LDR capture. Using tonemapping techniques such as with Photomatix, you can remap those tones, which is often used to bring the shadows up into the midtones and the highlights down to give a compressed tonal range, and sometimes to very good effect. This is especially good for spot work when used judiciously. Just brush in parts of the tonemapped image along with the original. In current terminology, this is called "pseudo-HDR".

An HDR "image" is actually an image file with 32-bit floating point values that scale from pitch blackness to (roughly of course) the surface of the sun, and everything in between. The Radiance format is the one that is most often used, but there is also a floating point TIF representation. This "image" can contain too much range of luminosity to display on ... anything. To make it, you have to collect data, but your camera only collects 8-10 stops at a time. You want to collect maybe 16-20 or so stops of light information, so you have to take 5 or more images two stops apart. Then you take those LDR images and convert them to HDR by feeding them to, say, Photomatix, which is able to read all the exposure information from the EXIF and figure out how to normalize the light values in each exposure, average them together, and come up with a 32 bit floating point number (one each for R, G and B).

Since you can't display this HDR image on anything, you have to come up with a way to map the light values onto visible tones on your display, paper-ink set, or what-have-you. That's the tonemapping step, and there are several ways to do it, the best of which involve computations on local features that sort of mimic what your eye does. Overall, tonemapping is just way to determine how to fit ('map') the huge range of light values you've collected onto the much narrower range of the viewing medium. When you think about it, the problem isn't that different from what painters and illustrators have had to do for centuries, which is partly why HDR images can look reminiscent of paintings and illustrations.

Best advice...always shoot uncompressed RAW files, 14-16 bits if you got 'em. Capture to 16-bit TIFs with the most neutral, linear capture you've got. Don't try to spruce up the images in this step with tone curves, etc. Don't use JPEGs--they have very low dynamic range. And don't bother doing white balance until after tonemapping.

Sooner or later, you'll be able to do this kind of stuff in camera, I think.

Take care, Luke
 

Lizard Of Oz

Demented Avenger
Oct 25, 1998
10,593
16
38
In a cave & grooving with a Pict
www.nsa.gov
First to untangle terminology a bit. A single shot exposure is a low dynamic range image (LDR), something that typically has 8-10 stops of usable dynamic range in it. With a good photon counter like the D3, you can get surprisingly clean capture right down to the lowest bit, so there is quite a bit of detail in the shadows of a very good LDR capture. Using tonemapping techniques such as with Photomatix, you can remap those tones, which is often used to bring the shadows up into the midtones and the highlights down to give a compressed tonal range, and sometimes to very good effect. This is especially good for spot work when used judiciously. Just brush in parts of the tonemapped image along with the original. In current terminology, this is called "pseudo-HDR".

An HDR "image" is actually an image file with 32-bit floating point values that scale from pitch blackness to (roughly of course) the surface of the sun, and everything in between. The Radiance format is the one that is most often used, but there is also a floating point TIF representation. This "image" can contain too much range of luminosity to display on ... anything. To make it, you have to collect data, but your camera only collects 8-10 stops at a time. You want to collect maybe 16-20 or so stops of light information, so you have to take 5 or more images two stops apart. Then you take those LDR images and convert them to HDR by feeding them to, say, Photomatix, which is able to read all the exposure information from the EXIF and figure out how to normalize the light values in each exposure, average them together, and come up with a 32 bit floating point number (one each for R, G and B).

Since you can't display this HDR image on anything, you have to come up with a way to map the light values onto visible tones on your display, paper-ink set, or what-have-you. That's the tonemapping step, and there are several ways to do it, the best of which involve computations on local features that sort of mimic what your eye does. Overall, tonemapping is just way to determine how to fit ('map') the huge range of light values you've collected onto the much narrower range of the viewing medium. When you think about it, the problem isn't that different from what painters and illustrators have had to do for centuries, which is partly why HDR images can look reminiscent of paintings and illustrations.

Best advice...always shoot uncompressed RAW files, 14-16 bits if you got 'em. Capture to 16-bit TIFs with the most neutral, linear capture you've got. Don't try to spruce up the images in this step with tone curves, etc. Don't use JPEGs--they have very low dynamic range. And don't bother doing white balance until after tonemapping.

Sooner or later, you'll be able to do this kind of stuff in camera, I think.

Take care, Luke

Wow. Thanks Luke. Very good information.
 

sid

I posted in the RO-me thread
and all I got was
a pink username!
Oct 20, 2005
2,140
0
0
Yellowflower.jpg

Hats off to you, sir. Marvellous!
 

sid

I posted in the RO-me thread
and all I got was
a pink username!
Oct 20, 2005
2,140
0
0
Thanks :) Is it possible to turn off the dates now? cause the dates dont appear in the thumbnails.
 

Juggalo Kyle

Sup brah.
Mar 23, 2005
1,290
0
0
36
Northern Cali
I finaly got my Wife to let me take a few more photos of her. I wanted to test out some more studio light.

These photos were taken on my Canon Rebel XT (350D) with my Canon 50mm f/1.8 lens (The Nifty Fifty).

I also took this photo to test out a method I thought of for making soft skin. Worked out pretty well if you ask me.

If you want to know the method, just ask. (It's seriously, really simple)

-Kyle
 

BillyBadAss

Strong Cock of The North
May 25, 1999
8,879
60
48
48
Tokyo, JP
flickr.com
I finaly got my Wife to let me take a few more photos of her. I wanted to test out some more studio light.

These photos were taken on my Canon Rebel XT (350D) with my Canon 50mm f/1.8 lens (The Nifty Fifty).

I also took this photo to test out a method I thought of for making soft skin. Worked out pretty well if you ask me.

If you want to know the method, just ask. (It's seriously, really simple)

-Kyle

Please explain. It's always interesting to learn something new. :)
 

Juggalo Kyle

Sup brah.
Mar 23, 2005
1,290
0
0
36
Northern Cali
Alrighty. It's quite simple.

First off, You'll need Photoshop, or GIMP, or some photo editing program that uses Layers. I have Photoshop.

1. Open the image in Photoshop.

2. Duplicate the background Layer.

3. Highlight the background layer, and use about 10 pixels of Gaussain Blur.

4. Since your copy should be on top, you cannot see the blur effects. Highlight the copied layer. Take your eraser tool, with from 25-35 Opacity, start erasing the areas you want softer, from the copied layer.

5. Use a big sized eraser for the big areas, like cheeks, foreheads, or any other big part you want soft.

6. Use a much smaller eraser size for areas like between the nose and lips, around the eyes, etc.


And voila! Simplicity with good results.
 

sid

I posted in the RO-me thread
and all I got was
a pink username!
Oct 20, 2005
2,140
0
0
Juggalo, thats sounds pretty cool, gonna try it sometime thanks, man :tup:
 

Lizard Of Oz

Demented Avenger
Oct 25, 1998
10,593
16
38
In a cave & grooving with a Pict
www.nsa.gov
Playing around with high ISO and high-contrast B&W.

B&WBoog.jpg

Only resized and converted to JPG in photoshop.

EXIF:
# Exposure Time (1 / Shutter Speed) = 1/30 second = 0.03333 second
# Lens F-Number/F-Stop = 2/1 = F2
# ISO Speed Ratings = 3200
# Focal Length = 35/1 mm = 35 mm