HDR questions

[Frog]

I recently saw a thread by ravensmore in the critique forum and then had to look up hdr as I hadn't heard the term before.
I'm getting mixed information elsewhere so am asking here.
The examples I've seen are quite dramatic but of course they are from sites trying to sell me something.
Some are saying the same thing can be accomplished with layers in photoshop.
Is this true?
I'm using photoshop elements 5.0.
I see there are plugins or upgrades for cs2.
Is it just easier than using layers to accomplish the same thing?

All info will be greatly appreciated.

[Medley]

hdr is short for high dynamic range, if you havn't already figured that out in your searching. You start by taking anywhere from 3 to 9 (in my case the max is 9, but you could conceiveably do more) photos of the exact same frame (tripod usually requred) at differing exposure values. The exposure values are achieved (under normal circumstances anyway) by varying the shutter speed, as it is important to keep the depth of field constant. Normally, when I do hdr, the middle photo is the correct exposure (ev0) and the 4 on either side are stepped in set increments. The more photos I use, the smaller I generally make my increments. 9 photos would either be half or two-thirds stop increments. So if I use half stop increments, I have 9 photos ranging from -2ev to +2 ev. I hope I've written that so that it makes sense.

If you use Photoshop's 'Merge to HDR' (File>Automate>Merge to HDR) command, the hard part (getting the photos) is over. Photoshop is rather adept at merging the photos- so long as the frames are exactly the same, and you want to adjust shadows and highlights equally The result will be a photograph that has the maximum amount of digital information in each light range, and generally has a greater light range than the camera itself is capable of capturing- hence the initials HDR.

All of this will likely be most noticeable in the shadows, where most digital images have a dedicated lack of digital information.

You can also import each photo to a new layer in a document and merge them manually, but even if you know the process well, it will take you a couple of hours to achieve what the program can do in a few minutes. The biggest advantage to this method is you can line up photos that don't match exactly- Hand-held images, for example.

I'd love to be able to tell you how to accomplish all this in Elements 5.0 (or even to tell that it's possible), but I have CS2 and so have no experience with any of the Elements software.

Hope this has enlightened you some though.

-Joe U.

[Greg McCary]

hdr is short for high dynamic range, if you havn't already figured that out in your searching. You start by taking anywhere from 3 to 9 (in my case the max is 9, but you could conceiveably do more) photos of the exact same frame (tripod usually requred) at differing exposure values. The exposure values are achieved (under normal circumstances anyway) by varying the shutter speed, as it is important to keep the depth of field constant. Normally, when I do hdr, the middle photo is the correct exposure (ev0) and the 4 on either side are stepped in set increments. The more photos I use, the smaller I generally make my increments. 9 photos would either be half or two-thirds stop increments. So if I use half stop increments, I have 9 photos ranging from -2ev to +2 ev. I hope I've written that so that it makes sense.

If you use Photoshop's 'Merge to HDR' (File>Automate>Merge to HDR) command, the hard part (getting the photos) is over. Photoshop is rather adept at merging the photos- so long as the frames are exactly the same, and you want to adjust shadows and highlights equally The result will be a photograph that has the maximum amount of digital information in each light range, and generally has a greater light range than the camera itself is capable of capturing- hence the initials HDR.

All of this will likely be most noticeable in the shadows, where most digital images have a dedicated lack of digital information.

You can also import each photo to a new layer in a document and merge them manually, but even if you know the process well, it will take you a couple of hours to achieve what the program can do in a few minutes. The biggest advantage to this method is you can line up photos that don't match exactly- Hand-held images, for example.

I'd love to be able to tell you how to accomplish all this in Elements 5.0 (or even to tell that it's possible), but I have CS2 and so have no experience with any of the Elements software.

Hope this has enlightened you some though.

-Joe U.

Thanks for the quick tips, But I understand why one would use HDR to balance a landscape picture, sky to foreground, and I have used it. But I don't see going to the trouble for a picture where the lighting is balanced well. I think that HDR may be over used some? Unless I am missing something?
Greg

[Medley]

hdr does lend itself to landscapes, and in fact that's about all I use it for. What hdr does NOT lend itself to is shots of opportunity, which comprise most of my work.

But, to answer your question, I think the benefit of hdr has to do with the way digital cameras "see" light. If you and I look at a light bulb in a large dark room, we see a gradual progression from the lightest areas into the darkest areas- a gradient if you will.

But capture that image using a digital camera, and the 50% of the information that the camera's sensor captures will be in the brightest area. 25% will be in the next brightest area, and so on down the line. In a digital camera with a 5 stop dynamic range, the 5th range (darkest shadows) contains 3.125% of the total information in the shot. Now, in-camera and post processing can (and usually does) balance this out some. Even your method of shooting can help. Once I learned this, I adapted my RAW shooting technique by shooting the scene as over-exposed as I possibly could without blowing out the highlights. In the processing stage, I darkened the shots back to normal exposure, thereby pushing some of the information in the lightest stops down into the shadows. My photography took a leap forward as a result. Still, your dealing with a finite amount of information, and adding to one lightness range means subtracting from another.

The theory behind hdr, then, is to take from each photograph the area that contains the most information, and combine them into one image. The result is an image that has more information, more detail, in every brightness range. You haven't robbed the brightest range to feed the darker ones, so even that range has more detail- if only a little. Use enough source images, and you add brightness ranges as well- increasing the dynamic range of the image.

But hdr does have it's limitations. Get a gentle breeze blowing through a landscape, and even your perfectly framed shots don't line up right. Leaves rustle, trees sway, etc. You have to change the settings after every shot, and without a remote that can do this you're going to have a tough time doing so without moving the camera. My Rebel XT creates images that have some 3000 pixels across the width of the photo. Even on a tripod, how much do I have to jar the camera to make the next frame 1 or 2 pixels off?

So there are advantages and disadvantages- just like anything else.

-Joe U.

[Old Timer]

This is a great explanation. Thanks I'm going to try this the next time I'm out with the tripod doing landscapes. I have to admit I had never heard of HDR and was a little at a lose when I read the thread Frog referred to. I'm glad to know I wasn't the only one in the dark.

[Frog]

Thankyou for the explanations. They're much more succinct than the ones I've read.
I have people telling me, the same thing can be done in photoshop but I had in the back of my mind that it would be a lot more work.
Old timer, I'm in the dark, much of the time, too. Seems like I don't know what half the stuff in a store even is anymore.
When I see something in photo threads I don't know, I look it up and Ravensmore thread in critique peaked my interest. Now I'm getting a headache. I think my memory may be full ;-)

[Medley]

For those of you who may be interested in what a difference HDR makes, here's a visual comparison. The first image is straight out of the camera, and was used as the middle (ev0) image in a HDR merge. The second is the result of that merge, and shows the strengths of HDR:




-Joe U.

[ravenmore]

Hey all - didn't realize I'd sparked this thread. I think HDR is the shiznit for landscape and architectural photography. I'll see if I can post the original photos and the hdr photo from my hdr photo in the critique section. The differences are pretty dramatic.

The program I used is the trial version of Photomatix. It makes the process pretty straight forward and easy. The sell a stand alone version and a photoshop plugin version. I think its about $100, so its not cheap but it sure is nifty. If there are other options out there I'd love to hear about them.

[ravenmore]

Here's the hdr images:

[Frog]

Thankyou all!
This forum site is the greatest and whenever I want to know something even slightly technical, I can find it here.

[ravenmore]

Here are the bracketed images I used for the above hdr images. I uploaded them a bit smaller than the final hdr's to make them easier to see as a group.:





AND for the other photo:





I combined each of these groups of 3 images into 1 hdr image (I checked the align images before combining option) to generate the initial hdr. I then had Photomatrix tone map it for me to the final images you see a couple of posts above.

[jixline]

i have found HDR to be also good when taking pictures of partly shadowed areas also, especially buildings