High Dynamic Range Imaging

[Darren Addy]

For those of us interested in getting the most out of our digital photography, I pass along the following links:

What ARE HDR or High Dynamic Range images? Perhaps the dawn of a new era.

In computer graphics and cinematography, high dynamic range imaging (HDRI for short) is a set of techniques that allow a far greater dynamic range of exposures than normal digital imaging techniques. The intention is to accurately represent the wide range of intensity levels found in real scenes, ranging from direct sunlight to the deepest shadows. - Wikipedia page on HDRI

HDR in Photoshop CS2 and another explanation (and a third). Note that most of these seem to be based on combining multiple shots of the same scene at different exposures. This is not optimal for stormchasers, where the storm is evolving/moving. The same thing should be possible with various "shots" extracted from a RAW file. This last link promises a tutorial on "building an HDR image from a single RAW file, soon!". I look forward to seeing that.

Soo Photography tutorial

PhotoMatix: HDR photo software & plugin - Tone Mapping, Exposure Blending & HDR Imaging for photography and a Flickr tutorial on using Photomatix (along with tutorial Part 2. Examples of the guy who produced this tutorial's work. The Flickr HDR pool.

This is bound to be somewhat controversial. What say you?

Darren Addy
Kearney, NE

 

[Jeff Snyder]

That's one of the benefits of bracketing exposure... Most dSLRs will let you bracket -- meaning that it'll take one shot that is well exposured (per the auto-exposure sensor on the camera), one shot that is underexposed (the amount is usually user-settable), and a third that is overexposed. You can set these as layers, and use masks and transparency to 'overlay' the three images on top of each other, letting you "make" an image that is probably more accurate relative to how our eyes saw it. I've never really done this, but I suppose it'd be most practical during structure shots (not when the adrenaline starts going during a tornado, when I'm too swamped trying to videotape, take pictures, look at road options, etc).

 

[Ryan McGinnis]

I feel so ignorant for not knowing about this, considering what a freakin' nerd I am and the fact that using Photoshop is part of my job. Guess I'll be filling up the CF card even faster now with all of those bracketed shots!

 

[John Diel]

Jeff,

I think what you're talking about here is "Blending" the different exposures rather than the HDRI process. From a cursury glance at the articles, this is a software process that starts with the "Blending" process and somewhere adds something within the programming.

I've used blending several times in photography. Not bracketing though. I use it frequently when shooting waterfalls, or areas with great differences in contrast. I espose the first shot as I would normally expose just about any shot that I take. I use all the standard techniques, light meters, etc. and try to pule a really nice shot. This is my baseline I use for comparison.

My second shot is exposed for the highlights. Basically, I want a good exposure where the highlights aren't blown out. It's deliberate and a new set of settings within the camera. Shutter, Aperture have changed to meet the needs to properly expose the bright area. I'm not worried about under exposure here. The shadows come in the next step.

The third shot is done the opposite of the second. I am now setting the camera to properly expose the shadow areas. I do worry about underexposure here as I want to see what's in the shadows rather than hiding it. I am not worried about over exposure as I have that properly exposed with the previous shot.

About the only thing that stays the same is the White Balance. I will also leave the C-PL Filter in it's position if I'm using one at the time.

I take the two photos and "blend" them in photoshop. I use the various masking techniques that have been around a while to do this. The HDRI goes way deeper into the tones and other areas of the image I don't deal with. Obvioulsy, the HDR! produces a very nice image.

 

[Darren Addy]

Just to follow up on what John said: What are the differences between Exposure Blending and HDR merge/Tonemapping?

Darren Addy
Kearney, NE

 

[Greg Campbell]

FWLIW, I've got no problem with this sort of image combining, IF the images are taken concurrently, or in quick serial succession. In the end, you can wind up with an image that is actually more "accurate," in that it's closer to your eye's perception. Outdoor Photography(?) published an article a month or two back, arguing that a merged image is much truer to 'reality' than a similar scene that had been dynamically compressed using a fill flash, split-ND, or other artificial means.

(When people start combining subjects that are temporally or spatially seperate, the whole concept of a 'photograph' goes out the window. Cut-and-paste lightning and photoshopnadoes are just plain lame.) :angry:

I'm planning on trying a dual-camera setup come monsoon season. Nighttime lightning scenes contain monstrous dynamic range and it can be very tricky to meter/guess a good compromise exposure. I'm going to tery two (film) cameras, identical lenses, and equal, simultaneous, exposure lengths. Will vary the aperture on each camera, attempting to retain more overall tonal detail.

-Greg

 

[Robert Edmonds]

That's kinda cool I'll have to try that. I personally like combining pictures you can see from first page on the website. I just don't like it when people pass doctored photos off as undoctered. However, photography doesn't go out the window. Some of the most well know photographers play with there photographs. The question is when does playing with photographs not make it photography? Personally I think that's a personal choice, because to some degree all pictures are "played" with. I mean you choose an exposure or frame that can contrast or emphasize something may not seem real. I took a picture once with a gumball and a contrail with a high flying plane. The camera store thought it was space scene.

 

[Jason A.C. Brock]

That's kinda cool I'll have to try that. I personally like combining pictures you can see from first page on the website. I just don't like it when people pass doctored photos off as undoctered. However, photography doesn't go out the window. Some of the most well know photographers play with there photographs. The question is when does playing with photographs not make it photography? Personally I think that's a personal choice, because to some degree all pictures are "played" with. I mean you choose an exposure or frame that can contrast or emphasize something may not seem real. I took a picture once with a gumball and a contrail with a high flying plane. The camera store thought it was space scene.
[/b]

When someone has the time could someone on ST maybe write up a short tutorial on blending photos? I have tried this on photoshop but cant ever seem to find the blending thumbnail that is supposed to be there.

 

[John Diel]

When someone has the time could someone on ST maybe write up a short tutorial on blending photos?
[/b]

Jason, try this site. It's about the best explaination and way better than I can explain.

Luminous Landscape Blending

 

[Darren Addy]

I've been searching for more info on creating HDR images from a single RAW shot. This should be possible since a single RAW image contains all of the dynamic data found in a series of bracketed JPEGs. (Note that I have not done this myself, as I don't even own a "real" digital camera that shoots RAW yet... but it is definitely on my list).

The big advantage to doing this from a single RAW shot is that: you just need one image, so no need to use a tripod, no need to remember to auto bracket and it will also work if the subject is moving. Much more what "fits the bill" for a stormchaser's requirements.

Step 1 is to a take your RAW shot and export (Save As...) some 16-bit TIFFs from it at various EVs. It sounds like most RAW processing software should do this, but if your's doesn't you can use the FREE RAW Shooter Essentials. (If you don't yet have RAW Shooter Essentials, I highly recommend downloading it NOW).

If you are using RAW Shooter Essentials, I can break down Step 1 into the following:
a. open your RAW file in Raw Shooter Essentials (the free version suffices)
b. choose "none" from the "metadata" drop-down box
c. change the exposure as you like (remember the EV - write it down for each image)
d. save as tif 16 bit
e. repeat for other EVs as you like

Now you have a series of TIFFs that are different EVs (example set: 1.5 under, 1.0 under, Normal, 1.0 over, 1.5 over).

Step 2: You are going to combine these images with HDR software to achieve the results you want. While PhotoShop CS2 has a plug-in for this, from everything I've seen you get better results (simpler too) from Photomatix Pro (a free trial version is available which will watermark your images, but would be a good way to test this whole process out without spending ANY moola). The Flikr tutorial (Part 1 and 2) in my original post show how to do this. EDIT: and here's another nice tutorial in PDF.

Since you have multiple EVs, you can use BOTH Photomatix's exposure blending AND tone mapping capabilities to create your HDR image. If you want to do tone-mapping ONLY you can skip Step 1 above and do that from the Single RAW image without making multiple EV copies. See the Photomatix FAQ for more details/tips. Also, if you are interested in doing tone mapping only, Photomatix is available as a Photoshop plug-in instead of buying the full-fledged standalone program (which is available for Mac or WIN).

Some of these HDR images look too "plastic-y" to me. The Flickr tutorial says that if this is the case you can just dial down the "Strength" applied to the HDR conversion (in Photomatix).

If your camera does not have RAW capabilities, you can still create HDR by either manually bracketing multiple shots or using the autobracket setting (if your camera has one). This will require the tripod and will work best on a non-moving subject (.etc).

There are other HDR software tools out there, but it certainly appears to me that Photomatix is the product to beat. See: Artizan and HDR Shot (which I believe is free for academic use)

Hope you find this useful and post some of your results!

Darren Addy
Kearney, NE

 

[John Diel]

The big advantage to doing this from a single RAW shot is that: you just need one image, so no need to use a tripod, no need to remember to auto bracket and it will also work if the subject is moving. Much more what "fits the bill" for a stormchaser's requirements. [/b]

Darren,

As much as I would like to believe so, I just can't see a single image having all the information required to do a true blending in either the more traditional manner or HDR.

Once hightlight detail is lost on an over exposure, it's lost. It works the same way with film. You over expose it, that's it, the detail is lost.

Underexposure works much the same way, but you can generally recover more detail on the underexposed shot. The detail washes out as you increase the brightness to get the detail, but it's way better than the alternative.

A single image, be it RAW, TIF, or JPG, simply doesn't have the dynamic range available to do this. Hence, the blending procedure of 2 or more different exposures. It also depends almost entirely on the range of the CCD or CMOS sensor and how much information it actually captures. Though it's agreed that capturing in RAW will capture more dynamic range information, I don't know of a consumer image sensor yet, that will capture what the human eye captures and it able to discern. That's the theory behind the blending and HDR processes we see here. They are attempting to take several exposures and create an image as close to what our eyes perceive when we look at the scene.

Example: When you walk into a room, you are generally able to "see" just about anything you look at whether it's in bright light, or a shadowed area. Our eyes and brain automatically adjust everything to enable us to "see" everything we can.

A camera isn't able to do this. is isn't able to adjust everything to capture as our eyes do. It's a single image. That's why we take the multiple images and "blend" them to get as true to what we actually see.

 

[Darren Addy]

John,
According to the Photomatix FAQ I linked to in my last post, you are identifying the correct issues and depending upon the dynamic range of the scene (and the exposure used to capture the single RAW file) you may not be able to match what you can do with multiple exposures. But with some scenes you can. Also if you are only interested in using the tone mapping functions you can work from a single RAW (granted the exposure blending would probably be necessary for storm shots).

I have no RAW files to try it with, so this all Book Learnin' at the moment. I'd love to see some of you with RAW storm files to try the trial version of Photomatix and post some results here. (And I'm probably not the only one) hint hint. Share those 'oliday shots (wink wink, nudge nudge)!

Darren Addy
Kearney, NE

 

[Mike Umscheid]

Great discussion on HDR and digital photography. A lot of landscape scenes, especially the sunsets/sunrises or any subject (i.e. a supercell updraft) facing the sun will have a fairly huge dynamic range equivilent to a huge number stops of light (maybe 9 or more stops!). I am finding more and more with my RAW conversions, that as long as you do not blow out any highlights (or very few pixels at 255,255,255) in a contrasty scene, I can get a pretty good "blended" exposure from one RAW image up to about about 6 or 7 stops of light in one scene. RAW is pretty darn powerful and it's amazing what you can recover deep in shadow if you are exposing more towards the highlights. Beyond about 6 stops of luminosity contrast, it's almost impossible to recover deep shadows if you expose for the highlights (e.g. a bright sky) even with RAW exposure compensation. There is a limit, but RAW exposure compensation is an amazing thing as long as you have at least *some* shadow information and you expose the highlights almost to the clipping point. I have turned a number of my storm photos into great pictures from one exposure using a very simplified HDR method of blending a +1.7 EV (for the ground) a +0 (for the main subject, like the storm updraft) and a -1.0 EV for example to recover some washed out blue sky. Here's a result from one such manual HDR:

Here is another from last week's chase in OK where I had a hard time with light contrast of a supercell updraft facing the sun. This one I used two blended RAW exposure compensations (I think a +0.3 and a -1.0)

I use RawShooter Premium 2006 which is an *excellent* RAW converter. The premium version allows for detailed white/black point setting of the RAW data using curves/levels (which the free version doesn't allow). It has really enhanced my workflow, and I'm in progress now of re-processing much of my 2005 storm photos since I have only used RawShooter Premium since about December. I use Paint Shop Pro X to blend my exposures and do all the final contrast/saturation tweaking as well as noise reduction and resize/unsharp mask.

Mike U

 

[John Diel]

I'd love to see some of you with RAW storm files to try the trial version of Photomatix and post some results here. (And I'm probably not the only one) hint hint.[/b]

OK, here's an old one done with 6 images that were bracketed rather than properly exposed. It's also a vertical stitch.

The first three images were of the upper portion of the storm and the next three were of the lower. The entire sequence of images was taken in about 4 seconds, so the storm motion wouldn't show up.

This is about the only one I have online. The others are all printed and archived over to DVD. Too bad, I 've got a great one of a canoe trip in Arkansas a couple of years ago.

 

[Darren Addy]

Wow, great stuff guys. I'm guessing that these are examples of the exposure blending only? Or did either of you try the tone mapping also?

I'm also really curious to see some examples using the Photomatix way (including the tone-mapping).

Keep it coming guys!

Darren Addy
Kearney, NE