Exposure blending is one way to merge multiple exposures into a single high dynamic range image. It’s thought to be better at creating natural looking HDR when comparing it to images produced by HDR software.
This technique is not just about selecting the right parts of the images to merge and then merge it manually. It’s also about having total control over how your HDR image ultimately look.
The main challenge in exposure blending is keeping the overall effect of the image natural. Without a smooth transition between the exposures, the blended image will not look harmonious and likely to be unusable.
Unlike other selection tools, luminosity masks are self-feathered which is ideal to achieve that smooth transition. The luminance based selection methodology also provides a quick and efficient way to create selections for blending.
In this tutorial, you’re going to see how luminosity masks can help you work faster, better and more productive in the blending workflow.
Although I use Photoshop, the post-processing steps explained here are generic and the same principles can be applied to other software that supports layer masking.
The details of luminosity masks are thoroughly explained in this article. But for the purpose of this tutorial, I’ll explain it in brief.
Luminosity masks is a post-processing technique to create selections in your image based on the luminosity value of the pixels. It was pioneered by a photographer called Tony Kuyper.
The benefit of luminosity masks is the precise and quantitative method of making the selection. Also, the self-feathering nature of the masks is what makes it unique and preferred by photographers.
Finding Luminosity Masks
You have to remember that it’s not a standard tool in Photoshop.
It’s ‘hidden’ in the Channels Panel!
Almost everyone I know who uses this technique has a Photoshop Action or a panel to automate the creation of the masks.
How To Blend Exposures With Luminosity Masks
Personally, I prefer to blend with luminosity masks because it works for me every time.
I often shoot into the sunlight and I like to include the flares to add energy to my image.
Without luminosity masks, it would be extremely time consuming and challenging to blend in the flares from the darker exposure.
To get the best result, some planning ahead is necessary.
Blending with luminosity masks can essentially be broken down into three simple steps:
- Plan for multiple exposures
- Choose the right luminosity mask
- Blending in the exposure
#Step 1: Plan For Multiple Exposure
Every exposure blending requires a bit of planning beforehand, this is no exception for blending with luminosity masks.
What does it mean?
It means you should always shoot with post-processing in mind and constantly thinking which part of the image needs blending in with a darker or brighter exposure.
Commonly, the sky needs a darker exposure to blend in. Also, consider the foreground elements because it can often get underexposed.
You can’t always judge if there’s highlights or shadows clipping, so use the histogram!
#Step 2: Choose The Right Luminosity Mask
Before you start…
You should stack your images in layers and choose an image as the base image.
“Which should be the base image?”
I normally use the image exposed for foreground or one that requires the least area to blend in.
Use An Image With Good Contrast To Create Luminosity Masks
You need to pick an image to generate the masks.
Before I explain further, remember that luminosity masks are created based on the luminosity value of the pixels in the image you use to create the masks.
So, to answer the question:
Choose an image that has good contrast. In the example above, you can use either.
This is because both images have good tonal separation for the sky and the foreground. When the masks are created, there will be one that targets the sky, which includes the flares fairly well.
Increase Tonal Separation For Better Masks
If the sky and the foreground have similar tonal range, the luminosity masks targeting the sky may bleed over into the foreground.
This defeats the purpose of using luminosity masks.
But there’s a way to get around this.
You can add a Levels/Curves adjustment layer to increase the contrast so that the darks become darker and the brights become brighter.
Now, create luminosity masks with the new tonal values and delete the Levels/Curves adjustment layer after.
Choose A Luminosity Mask Targeting The Highlights
Choosing the right luminosity mask helps you blend in the darker or brighter exposure more easily.
Going back to our image above, we want to blend in the darker exposure for the sky.
So, we need to choose a brights mask targeting the sky and the flares only, or at least most of it!
We may not find the perfect mask but one that’s close enough will do just fine.
Looking through the brights mask, Brights 4, 5 and 6 are definitely out.
They are too restrictive and the flares are being cut out.
So, the question is:
Which would you choose, Brights 1, 2 or 3?
Brights 1 includes the foreground, which means the darker exposure may bleed into it.
That’s not an issue because you can use “painting a mask” technique. Essentially, you create a black layer mask, load the chosen luminosity mask and paint just in the sky with a white brush to reveal the dark exposure.
Brights 2 looks about right, but is it too restrictive for the sun flare?
Experiment With An Open Mind
Technically, you can also blend using Brights 1 and Brights 3 mask. The result may be different but the image will definitely look natural and usable.
So, when editing with luminosity masks, keep an experimental mindset and try out different masks to see which gives you the best result.
#Step 3: Blending In The Exposure
Once you’ve found a mask, the rest is pretty straightforward.
You can either load the mask directly onto the layer mask, which will blend in the exposure for you directly or…
Use the “painting a mask” technique, which I’ve explained above.
I prefer the latter because it gives me more control over where to blend and its opacity.
Blending More Exposures
When you know how to blend two exposures, you can repeat the steps to blend as many exposures as you want!
The key to remember is always have in your mind what and how you’re going to blend while shooting the scene. Selecting a mask is the matter of experience. This means every minute spent editing with luminosity masks makes you better at it each time.