Mikes Photography

jonH · Posted: Sun Dec 03, 2006 9:48 pm Post subject: Intro to HDRI (bandwidth warning)

(This post was originally made in the photographymonthly forums)

Before I start this marathon intro into HDRI, I have a quick disclaimer Smile

I am not the world's foremost expert on either Photography or HDRI. Rather than take what I say as gospel I encourage you to go and play, and find out for yourself what's possible with the technique.

There is a goldmine of amazingly good, and shockingly bad HDR/Tonemapping examples on flickr, so I'll suggest that as a place to start. I've listed some of the main groups that i've stumbled across over the last few months at the bottom.

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We all know that cameras only have a limited dynamic range (about 5 stops for a 12-bit raw), far less than the human eye. It's something that photographers have always lived with, and usually can be taken advantage of. There are times however, where the limited dynamic range is a bind, not a blessing. We've all suffered from exceedingly tricky lighting conditions - it's where the serious photographers shine at getting the results they're looking for where the rest of us tend to hope for the best and often end up being disappointed. Although most cameras are going to let you bracket 1/3 or 1/2 a stop either way there will always be the situation where you're still going to lose something, beit details in the shadows or details in the highlights..

or are you?

The basic principle of HDRI is quite straightforward - expand the dynamic range by taking information from a range of differently exposed images of the same subject and saving it in a single high range (usually 32-bit) image.

It might sound like a lot of extra work, but if your camera has an auto bracket mode then half the work has been done for you already. My default starting point is to set my D70 to bracket 2 stops apart using the AEB function. Just think about how much extra detail you could capture using an exposure range like that - there's nothing that can compete using just one exposure. You can bracket closer, but the effect will be less pronounced.

There's nothing stopping you taking more than just the 3 auto-bracketed images either (The D200 can AEB for 5); there's a lot more manual intervention in this case so it's not always suitable, and you'll only see a significant improvement when there's a very wide range to be captured.

I'm going to use a shot from my parent-in-law's farm taken in September as an example. It's not the world's best photo, but should give a good example of a situation where there's a case for using HDR.

The sun was just off to my right and was quite strong with it. Because of where the tractor was parked, I couldn't get a shot from the 'sunny' side, so had to set up in the shadow.

Nothing special about the settings - it's down to personal preference, but in this particular case the shots are taken 3 stops apart.

'Normal' (0ev):

+3ev:

-3ev:

Not particularly inspiring, are they? In fact, before I'd heard of HDRI/Tonemapping, I'd have quite happily binned them all.

The 3 shots are then merged into one HDR image using Photomatix. There are a number of different apps that will perform this task and I'm sure with the mini-boom that's occured regarding HDR there'll be plenty more in the near future Smile

When you load the image up, it'll look something like this:

There's so much range, that monitors can't show it - you'd have to play with photoshop using effects to see the difference in behaviour between it and an 8-bit image. Although the example here has been changed down to 8-bit jpg, what you see here is pretty much how you see it in photoshop when it's a 32-bit HDR.

Now the fun bit.. tone mapping Smile

To get that rediculously wide-ranged picture to something we can actually enjoy, we have to compress the range back down to LDR (Low Dynamic Range) again.

So what's the point?

The thing is, because software has more information to refer to than a straight single exposure, it can make better decisions on where to make the savings - details can be kept so the overall result is still far, far better than if we'd just taken the one photo.

I can't say I've delved particularly deeply into the mathematics of it all - the wiki entry goes into quite some detail regarding tone mapping if you have a spare lunch break to peruse it.

The photomatix cs2 plugin and the standalone app are fairly similar in operation - and there's some significant power at hand which you have to be careful with if you want your photo looking reasonably realistic Smile

With almost the default settings, and a slight contrast tweak, we're left with a reasonable result:

Photomatix allows quite a range of adjustments and some of them get pretty mad - it's certainly worth downloading a demo of the main contenders to see what you think - they tend to be fully functional but leave water marks on the final image.

We've still not achieved an ideal result with the above selection though. The range of light was so great that 3 exposures wasn't enough to capture everything, even at 3 stops apart - the clouds are still blown out!

Fortunately for me, the reality is I didn't take 3 shots as I usually do, I took 7, 1 stop apart :D I've since learned that ideally I should have really taken 9 images 1 stop apart, or maybe 5-7, 2 stops apart in this situation. As I said at the top, I'm still learning about this malarkey myself, but at least I've got a good example of where 3 images @ 3ev increments isn't quite enough!

To take 7 shots I metered, set to manual, then knocked it down 3 shutter speeds so the 'metered' photo was the middle exposure.

For completeness, here is a link to the 7 images (3 of which you saw earlier)

-3ev -2ev -1ev 0ev +1ev +2ev +3ev

If you look carefully at the HDR you can see there's more detail in the sky

and it's certainly visible in the tone mapped image:

And here endeth the lesson Smile

Hopefully there is enough info for you to want to perform further investigation should you be interested in having a play.

Here are the wikipedia links - they're quite informative and hold a selection of links that you may find useful to follow through

http://en.wikipedia.org/wiki/High_dynamic_range_imaging
http://en.wikipedia.org/wiki/Tone_mapping
http://en.wikipedia.org/wiki/Auto_Exposure_Bracketing

Here are some popular HDR pools on flickr - have a poke around, there are some very nice examples in there!

HDR
Pure HDR
TTHDR (True Tone High Dynamic Range)
Subtle HDR
Photomatix
Artizen HDR
HDR Skies

Finally, here are a few of my HDR images

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Simonzphotoz · Posted: Sat Dec 09, 2006 9:26 am Post subject:

awesome post...make it a sticky venom!!!
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Simonzphotoz · Posted: Sat Dec 09, 2006 9:29 am Post subject:

any chance of a step by step guide on how to!!??
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jonH · Posted: Sun Dec 10, 2006 12:47 pm Post subject:

Try checking out these links :

http://www.hdrsoft.com/resources/features.html

http://www.popphoto.com/howto/303...te-high-dynamic-range-images.html
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Venom · Posted: Sun Dec 10, 2006 2:24 pm Post subject:

creators · Posted: Fri Dec 15, 2006 10:34 am Post subject:

Thanks from me too for a great post, something I've never done or heard of before and one to try.
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Venom · Posted: Sun Dec 31, 2006 3:55 pm Post subject:

Right after talking with Adam and hil26 (Dave) we have all decided that jonH's HDR post is going to be the new post of the month.

So big thanks to John on a great and very informative post q43

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jonH · Posted: Mon Jan 01, 2007 4:49 pm Post subject:

coo.. thanks! PDT_Aliboronz_24

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richard · Novice Joined: 16 Oct 2006 Posts: 148 Location: Essex

Jon, ive been meaning to post up about this, but how and what type of images should i use?

Using PS2 and i get error messages about incompatible files when trying out HDR...thats using 16 and 32bit tiffs...

Could you let me know what i should start off with please?
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jonH · Posted: Sat Jan 13, 2007 11:15 am Post subject:

you usually get errors if you try to produce a number of images from the same raw file (creating over and under exposed images by means of exposure compensation during raw conversion)

photomatix looks at the exposure information to blend the images, so if all your images contain the same exposure info, it throws a strop.

if this is the case, strip all the exif out and manually set the bracketing range - that should sort you out.

if it's not the above, let me know, although i think the above does cover 99% of all merging errors
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richard · Novice Joined: 16 Oct 2006 Posts: 148 Location: Essex

Cheers matey.
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hil26 · Posted: Sat Jan 13, 2007 5:03 pm Post subject:

Richard

have a look at the photomatix website, they have a free download of the program (it puts watermarks on finished images - sometinmes it doesn't but that depends a little on what you done - but I go astray.)

It also allows you to play with a single image - it's well worth trying out, and it also gives some very good examples.

Can find it here

http://www.hdrsoft.com/index.html

Venom · Posted: Sat Jan 13, 2007 5:07 pm Post subject:

I downloaded the one from here: http://www.photo-freeware.net/

Not had the watermark appear yet so............

Mike
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chris82 · Stacker! Joined: 08 Nov 2006 Posts: 508 Location: Belfast

Awsome thread,but I use a canon and I still havent learnt how to change settings.also on canon theres no ev (eg)-3ev -2ev -1ev 0ev etc...so what do I do for hdr on canon.I have been wanting to try hdr for some time now.I have heard a lot about bracketing but I dont know wher to start.Any tips.

jonH · Posted: Thu Jan 25, 2007 9:28 am Post subject:

You will habe AEB, trust me Smile

it might be called ABC (auto bracketing control) or something. I did a quick google and found this:

http://www.hdr-photography.com/aeb.html

All of canon's dslrs are listed there, so you'll just need to trawl your user manual for details

That said, you can always meter then switch to manual, and manually take the correct number of exposures - that's what i did for the tractor pics in the original post.
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jonH · Posted: Thu Jan 25, 2007 9:30 am Post subject:

wtf s-w-i-t-c-h o_O
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Venom · Posted: Fri Jan 26, 2007 10:50 am Post subject:

sean · Prawny! Joined: 24 Nov 2006 Posts: 235 Location: London

This is fantastic - excellent post

JenkiesLuv · Newbie Joined: 05 Apr 2007 Posts: 43 Location: California

I know this is WAY late lol but can you take a raw image and under and over expose it in Camera Raw and get the same results? Just curious because i tend to move alot when I'm composing my image and I rarely ever stand in the same spot for 3 frames LOL
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Evolution104 · 2Fast 2Furious Joined: 07 Jan 2007 Posts: 998

Generally yes. The effect may not be exactly the same, but should work well for starters. The only real problem with this is you're limited to the dynamic range of the single image you use which could result in clipping or limiting the effect. Multiple original images, when combined, will provide much more range for the software to work on.

But by all means, give it a go - I've had some success with it at times.
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JenkiesLuv · Newbie Joined: 05 Apr 2007 Posts: 43 Location: California

I have these images that I took this morning because my mother wants me to make her some wall art for her bathroom and I thought that would be really

on the flowers. When I took the pictures I bracketed manually but I also moved an inch or two to either side and adjusted my zoom LOL So NOW I have 5 bracket photos that are completely different of the same flowers and I can't use them because it doesn't look right. They won't superimpose correctly because they're different. I was trying to get around setting everything up again but it looks like i'm gonna have to anyway :-( Back to the drawing board uuughhhh
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hil26 · Posted: Mon May 21, 2007 9:15 pm Post subject:

In photomatix, one of the menu selections is for

Automate
Single file conversion

have a try with that, it can give some very good results from a single image
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JenkiesLuv · Newbie Joined: 05 Apr 2007 Posts: 43 Location: California

OMGoodness what am I doing wrong? I thought this would be cooler with my husband's Harley than flowers but when I did it I used 6 shots on a tripod all at different exposures. Now it's all pixelated LOL I mean from far away it's great except I need to do a little more editing in the wheels and things but the pixel mess is gonna drive me nuts on a print. Help please!

hil26 · Posted: Tue May 22, 2007 6:14 am Post subject:

Not too sure how much under/overexposed the shots were, but try it with 3 shots - one at -2EV one at 0 and the other at +2 EV.
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JenkiesLuv · Newbie Joined: 05 Apr 2007 Posts: 43 Location: California

that worked alot better, using only 3 photos. I think alot of the output depends on the picture you use...I might save this in my stash for the perfect moment. Thank ya'll for your help.
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Evolution104 · 2Fast 2Furious Joined: 07 Jan 2007 Posts: 998