My HDR Workflow | Part 2

In this blog entry I’ll finish sharing my current HDR workflow. In the first part of this series I talked about camera settings, using Lightroom to process a bracketed set of images, using Photoshop to merge the bracketed set into a 32 bit per channel HDR file and tone-mapping with Photoshop HDR Pro. If you haven’t read part 1 you can find it here.

This blog will share the remainder of my HDR workflow including how I tone-map images with Lightroom 4 and how I use layers (in Photoshop) to combine the best parts of two different versions of an image. I’ll also about some of the more technical details of HDR photography. I’ll be using the same F-4S Phantom II images I used in Part 1 for this entry including the 32 bit per channel .tiff file I saved after merging a three shot bracketed set with Photoshop.

32 bit/Channel Images

Warning: this section might get a little technical. If you don’t enjoy reading about stops and bits per channel you can go ahead and skip down to the section called: “Tone-mapping with Lightroom 4”.

My first experiences with High Dynamic Range images (HDRi) happened when I learned to use a unique camera called a Spheron Spherocam VR (now it’s called a Spherocam HDR). I used it to capture entire environments and all the lighting information in that environment. The RAW files that come out of the Spheron are 32 bits per channel and some are over a gigabyte in size. That is absolutely huge! Let’s compare what a Spheron can capture with what we see with our eyes and what a typical digital camera can capture.

The definition of a stop (in photography) is: a doubling or a halving of the amount of light. For example, if you are using a single light to illuminate a subject and you add a second (identical in placement, size and intensity) you have added a stop of light. If you add a third light you are not adding another stop, you’d need two more lights (for a total of four) to increase the light by another stop.

Our eyes are pretty incredible. Like the Spheron our eyes can see details in shadows and also see what is happening in areas of super high brightness at the same time (a very large amount of dynamic range). The human eye can see up to 24 stops of light (when the pupil is closing and opening for various light intensities). Most digital cameras use a 10 to 14-bit A/D converter so their (theoretical) maximum dynamic range is only 10-14 stops. 10-14 stops might sound like a lot of information, but this high bit depth only helps minimize image posterization (because total dynamic range is limited by noise levels). In reality, the dynamic range of a digital camera doesn’t come close to the theoretical maximum of 10-14 stops. A more realistic number is 5-9 stops of information for a typical digital camera.

So what does all this talk about stops mean in the real world? It means that even though we can see a wide range of light with our eyes a typical (digital) camera can’t come close to seeing what our eyes can see. The camera can only capture about half the information we see. If you set your camera exposure to see into dark areas of an image you’ll lose information in the very bright areas (this is usually called: “clipping the highlights). The result will be large areas of white in your image where there should be subtle changes of brightness. If you set your camera exposure to see all the detail in bright areas you’ll lose information in the dark parts of your image (this is usually called: “plugging the shadows”). The result will be large areas of solid black where you should be able to see some details. If you set your camera for a middle exposure you may lose both dark and bright information in your image. The bottom line – most digital cameras can’t come close to capturing everything we can see with our eyes.

A real world example of this dynamic range limitation happens when you take a picture inside but you have a window in your shot. If it’s super bright outside and you set your camera to expose for your interior the windows might be pure white in your image. If you set your camera to expose for what’s outside you can see everything in the window but the interior will be super dark. Neither looks very good.

High Dynamic Range cameras can capture up to 26 stops of information in a single capture (when using a special camera like the Spheron Speherocam HDR). The resulting file is a 32 bit per channel image. What does 32 bit per channel mean? Well, a typical jpeg image has 8 bits per channel and that means there can be as many as 254 different shades of grey between black and white (for a total of 256  when you include black and white) for each pixel in your image. That means a maximum contrast of 256 to 1. A 32 bit per channel file, on the other hand, can have over 4,000,000,000 different shades of grey between black and white for every pixel. That’s a lot of information. In fact, it’s too much information to view all at once on a typical computer monitor (the monitor on my MacBook Pro has a contrast ratio of about 619 to 1, for example) and that’s why the 32 bit per channel files look so bad when we open them in Photoshop. To get a good looking image we need to use tone-mapping on a 32 bit per channel file.

Tone-mapping is a form of dynamic range compression that lets you see information from the dark areas of your image and information in the bright areas of your image at the same time. Tone-mapping gives you what most people consider HDR photography (an image that seems to contain a massive amount of information including the brightest and darkest areas of an image).

If you’re not using a Spheron Spherocam HDR you’ll need to take bracketed sets of images to capture all the information in your scene and combine those shots into a single 32 bit per channel file. I talked about combining bracketed sets of images in part 1 of my HDR workflow blog.

Tone-mapping with Lightroom 4

To tone-map an image in Lightroom you first need to import your 32 bit .tiff file into Lightroom. You can do this by clicking the import button (in the Library Module) and locating your file. I created a folder (in my pictures directory) where I put all my 32bit files to make them easier to find.

When the file is imported it won’t look very good. At this point you can change over to the Develop module where you can really get the image to start looking good.

With our 32 bit/channel image imported into Lightroom it’s time to make some adjustments. As soon as you move into the Develop module the image should look better than the raw .tiff file looked. Now you can make some huge adjustments with the exposure slider. Unlike a typical RAW file (which has an exposure range from -5 to +5) you can now set your exposure slider anywhere between -10 and +10. And no matter where you set exposure the image will have considerably less noise than if you applied the same adjustment with a 16 bit/channel RAW file. I also like that Lightroom 4 doesn’t add glowing edges to an image like Photoshop HDR Pro will sometimes. The result of tone-mapping with Lightroom 4 is very natural looking. Here’s a look at my image after I applied my adjustments in Lightroom 4:

This looks really good if you ask me. There’s a pink color cast to the F-4S and I plan to take care of that in Photoshop. If you’re wondering what my adjustments were here’s a look at my basic adjustment panel:

The first thing you’ll probably notice is that I have my highlight slider set to -100 and my shadow slider set to +100. I do this to almost every 32 bit .tiff file I bring into Lightroom 4. If the image is still too dark (like this image was) I’ll increase the exposure. The cool thing is that all these moves won’t introduce a bunch of noise into your image (unless you didn’t perform a noise reduction on the bracketed set of images before merging them into a 32 bit HDR file). With the exposure settings done I’ll boost the contrast, add clarity (again you can usually add a lot without bringing much noise into your shot) and I’ll boost the colors with the vibrance slider. Sometimes I’ll need to make a white balance adjustment but I was pretty happy with how the colors looked overall in this shot. Occasionally I’ll open the HSL panel to make some color moves but that’s a subject for another blog entry.

And that’s all I’ll do in Lightroom. I don’t sharpen, add noise reduction or any other effects. I prefer to do all of those moves in Photoshop. If you’re not going over to Photoshop you can use the adjustment brush tool to remove some of the color cast from parts of your image and you can darken the edges by using the post-crop vignette slider (in the Effects adjustment panel). At this point you may be super happy with how it looks so you can just export the image as a jpg file right out of lightroom. Here’s a look at the F-4S image after I tone-mapped the file in Lightroom and I added some finishing moves in Photoshop:

I really like how this version turned out. Could I make it even better? Sure. One way to improve this image is to blend in a little of the Photoshop HDR Pro version.

Blending Different Versions of an Image Together

At this point I have three different versions of my F-4S Phantom II. I have a single exposure shot, a Photoshop HDR Pro tone-mapped version of the shot and I have the Lightroom 4 tone-mapped version of the shot. Sometimes I’ll find something I really like about each of the shots along with things I don’t like about each image. In the case of the F-4S I really liked the look of the jet fighter in my Lightroom version but I prefered the look of the environment in the Photoshop HDR Pro version. When this happens I’ll bring them both into Photoshop as layers and I’ll create a single final image.

There’s a few ways to get both images into Photoshop. You can use the Bridge, mini Bridge or you can import your jpg files into Lightroom and open the files into Photoshop from there. I used finder (explorer on a PC) to locate my files and I opened them in Photoshop by dragging the files onto my Photoshop icon in my dock. When I did this I had two files open. I chose one of the two files and I right clicked the background layer and chose Duplicate. In the dialog that opened there is an area called Destination where you can select the other file. Once I click OK I close the file. Photoshop will close the file and then you can see the first file but now it has two layers. I’ll select the top layer and apply a mask by clicking the mask icon located at the bottom of the layer panel. Here’s a look at the mask icon (circled in red):

With the layer mask (on the top layer) selected I choose the brush tool. With a white mask on the top layer I chose black to paint with my brush tool. Now you simply paint where you want to see the lower layer. If you make a mistake and reveal  too much of the bottom image just switch your foreground color to white and paint your mistake away. Once you’re done painting on your mask you can use the opacity slider to blend some of the top layer with the bottom layer. It’s just that easy.

Here’s a look at my final image when I used a layer mask to bring the floor and ceiling of the Photoshop HDR Pro version into my Lightroom 4 version:

After I’m happy with the blending of my two versions I’l flatten the image and perform any finishing touches like final color boosts, adding a glow effect and darkening the edges of my shot (adding a vignette). I talked about some of these finishing touches in another blog entry I wrote called: “Finishing HDR Images”.

And that wraps up my workflow for creating HDR images. If you have any questions feel free to ask them in the comments and I’ll do my best to answer them for you.

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