Anatomy of a HDR

JMcL

A few people have asked me to do a tutorial on creating HDRs, so here goes.

The examples here are done with Photoshop, but any imaging program that provides layer masks should work just as well (I've done this with GIMP, and I guess it should be fine with Elements, and probably Paint Shop as well). I'm making the assumption that you're comfortable using layer masks, selections etc.

Image Capture
The first step is to actually get the images. There are 2 possibilities:

1. Process a single RAW several time with different exposure compensations (don't try this with a JPEG. It just won't work)
2. Bracketed exposures

In both cases stop the lens down, especially if you want to have close foreground objects in the frame, so either use aperture priority mode, or better still manual.

Each has advantages and disadvantages. Using a single RAW will make sure that everything line up properly, but has the disadvantage that there won't be much detail in the shadows, and they'll suffer from noise (see here for an excellent explanation as to why)

If bracketing, you must mount the camera on a tripod, and I'd recommend using a cable release/remote control, but at least use the self timer. If you have mirror lock up, use that too. I'd also recommend switching to manual focus, as if the lens focus changes between shots, it can play havoc with lining up anything in the foreground. It seems like a lot of bother to go to, but it'll make the task of getting everything lined up later a lot easier. (Of course you're going to do all this anyway even if taking a single RAW, right? ) I usually auto bracket by about +/- 1 1/3 stops which gives me 3 exposures with a range of between 2 and 3 stops. I always shoot RAW when bracketing, so I have leeway to adjust the exposures further. The most important thing is to ensure that you haven't blown the highlights in the faster exposure, and you have enough detail in the slower one, so these are guidelines only, as what you'll need will depend on what's in front of the camera at the time.

Let's take these as examples of a set




Assembling the images
Start with the brightest image, and progress by adding each other image in the set as a layer (select the entire image Ctrl-A, Ctrl-C, and paste it on top of the main image), finishing up with the darkest.

Next, add a layer mask for all the non-background images. Create the mask in whatever way you want, to expose the layer below, but there are a few methods which work well.

• The gradient tool is very useful as a basic step, and will give you a result very similar to an ND graduated filter.
• Create a selection based on the layer content. Select/Color Range is very useful for this. In Photoshop, select for the highlights, in GIMP you can do something similar, and use the eye-dropper to select a colour
• Just use a paint brush

Combine several of these if necessary. Here are the layers and associated masks of the HDR. I've use the gradient tool to give the basic mask, and then the paint brush at various opacity levels to bring out a bit of detail in the cloud from the layer below.

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Final result


I occasionally add a channel mixer adjustment layer to give a kind of Velvia look (R:+120, G:-10, B:-10 or R:+130, G:-15, B:-15), though haven't in this case

Other points
The main thing to avoid is getting a "halo" effect in the HDR. The best way to avoid this is to ensure that any feathering on the mask overlaps into the shadow more than the highlight areas. Things tend to look more "wrong" in the highlight area, and a Ready Brek glow will be very noticable. If you have a few areas like this, paint into the mask with the brush on low opacity until the result looks right

Watch out for chromatic aberation on things like trees on the horizon (eg, the one on the top left here - the remaining CA is just a fact of life with the Canon 18-55 kit lens). Favour using the darker exposure to give a silhouette

References
Here are a few useful links:

Luminous Landscape digital blending tutorial

Video tutorial on the Radiant Vista

Roen

Cool tutorial,
thanks very much, we'll have to drag you out on the next Waterford meet!

JMcL

Roen wrote:

Cool tutorial,
thanks very much, we'll have to drag you out on the next Waterford meet!

You're welcome. Looking forward to the next meet, I missed the last one that was due to happen a couple of months back as I was in Dublin that week, though if I remember rightly the weather was absolutely foul

FX Meister

Can this be made into a sticky?

kjt

Great tutorial, I look forward to trying this out

jaggiebunnet

Me too - great tutorial thanks!

btw - whats an HDR?

kjt

High Dynamic Range. This is a lighting procedure designed to emulate the way that light levels in the real world vary over an enormous range. This is mostly achieved by the use of floating point textures and render targets (as well as using the appropriate lighting algorithm); integer formats do not offer the anywhere near the same range of values. Although visually better, the use of floating point formats can result in a large performance impact on some graphics adapters.

JMcL

kjt wrote:

High Dynamic Range. This is a lighting procedure designed to emulate the way that light levels in the real world vary over an enormous range. This is mostly achieved by the use of floating point textures and render targets (as well as using the appropriate lighting algorithm); integer formats do not offer the anywhere near the same range of values. Although visually better, the use of floating point formats can result in a large performance impact on some graphics adapters.

I guess strictly speaking these aren't HDR's. You can use CS3 or standalone software such as Photomatix to combine and blend images as you describe. I've tried Photomatix, but couldn't get satisfactory results from landcsape images, especially where long exposures with things moving between images are concerned. The approach I've described here is more analogous to using graduated neutral density filters on the camera (except that they would result in a single exposure), with some advantages (mainly you don't have to decide on a straight line across the image), and some disadvantages (moving things - trees, reeds etc - across the split will make a blend impossible)

kjt

Here's my attempt anywho.
I could probably make it look better if I put more time into it, but not bad for 5mins work.

shoutman

Hey anychance the broken images could be fixed?

JMcL

shoutman wrote: »

Hey anychance the broken images could be fixed?

Hmm. I'd hosted the images on geocities at the time, which is long gone. I doubt I have the working files anymore unfortunately (I do have the source image though). If I get a chance, I'll have a look, or maybe redo it if I can't find them

CabanSail

Give one of the mods a shout if you want any of the links edited.

JMcL

CabanSail wrote: »

Give one of the mods a shout if you want any of the links edited.

The problem that Geocities (where I'd hosted the working images) doesn't exist anymore - Yahoo pulled the plug a few years ago. I didn't put them on Flickr as I couldn't hack notion of a flood of invite to add an image of a layer mask to about half a dozen groups

I'll see if I can dig up the working files, though I'm pretty sure I don't still have them, as I've gone through a computer upgrade since. If not, as I say, I'll redo it for the craic to see how different my interpretation is 5 years on :-) I'll give yez a shout then to update stuff, or if it ends up looking completely different (probably, since I use Lightroom now, and have a preference for less saturation), I might repost it as an updated reply, and get ye to add a link in the original post

John

kelly1

I think you're describing exposure blending rather than HDR.

JMcL

kelly1 wrote: »

I think you're describing exposure blending rather than HDR.

Yup - as I said in post #8 (feck - 4 years ago to the day, well in about 20 minutes anyway). Same end result though - representation of a scene with a contrast range in excess of the 10 or 11 stops you'll get from a typical sensor (though nothing to stop you doing it with scanned film if you really wanted).