HDR Images. The easy way.

I've read quite a bit about HDR (High Dynamic Range) imaging recently. Up until now, my stock method of producing good, wide exposure photographs was to shoot three images, each a stop apart. Typically, I would then take the darkest of the images and the lightest of the images and use a faded composite to allow a nicely exposed sky to show through above a nicely exposed landscape.

All good, but what about where there are details in the foreground that are lighter? Or where the line between land and sky is not even roughly straight? How do you draw the line between the different exposures?

Well, after looking around and finding lots of tutorials about HDR images I decided to have a go at developing (pun not intended) my own technique.

Using Photoshop, I have been able to easily blend the darkest exposure with the lightest exposure and get Photoshop to do the difficult bit of deciding which bits of each image should show through to produce a final, wide-exposure image.

The first steps to producing an HDR image are getting (in my case) three different exposures. Some folks might use five, seven or even more different exposures but my technique hasn't developed that far yet.

However you do it, ensure that it is the exposure time you use to control the exposures as the aperture obviously has an effect on depth of field and can have some odd side effects when it comes to blending your final images. Although this could be interesting...

Anyway, you will typically have three exposures:

• A sky exposure. This means that the sky looks really good with lots of cloud detail, but the landscape looks dark or even black.
• A land exposure. This is where the landscape is well exposed, the grass is good and green but the sky is washed out or even white.
• A middle, or 'correct' exposure. The land and sky will ultimately be a compromise and will probably look weak and washed out.

Open Photoshop and load up your three images. You will need to organise them into layers, with your darkest exposure on top, your middle exposure in the middle and your lightest exposure at the bottom.

Obviously you used a tripod to take the three separate exposures. If you didn't, go get one and start again.

Your three layers will be lined up, pixel perfect. Now for the magic.

Your top layer, change its blend mode to Screen.
Your middle layer, change its blend mode to Multiply.
Your bottom layer, change nothing.

Yep, it looks a pretty mess. However, now the really clever bit. The middle layer is about to work as a kind of mask, allowing the dark bits from the lightest exposure to show through to the middle layer, and allowing the top layer to show its lightest exposure over the middle layer. We do this by doing two things to the middle layer.

First, we desaturate it because we already have all the colour information we need in the darkest and lightest exposures (the top and bottom layers).

Next, we invert it. This has the effect (because it is 'Multiplied' with the bottom layer) of darkening the light parts of the bottom layer. The top layer, being 'Screened', will add its light areas to the Multiplied bottom layers.

The result? See for yourself:



Not the most attractive image, I hope you'll agree, but it does show a wider range of exposures than certainly my camera is capable of.

The image does show a lack of contrast, but I think I can overcome that with some judicious leveling of the light and dark exposures.

I'll be perfecting this technique over the coming weeks and hope to have some better images to show you.