GND Filters vs. Exposure Blending : Which is Better?

 

This is a fantastic question – one that I have come across a lot lately. With the popularization of Photoshop, many are looking for a replacement to in-camera techniques. But the big question remains – is it better to capture what you want in-camera, or do it later in post process? How important is this to overall image quality?

 

WAIT – What are GNDs and why would I want to exposure blend anything?

 

While I go into a much better explanation of this in my most recent question here, the basis behind both methods is to level out your exposure. In short, when we photograph a landscape, we are often presented with a large difference in exposure (i.e. the amount of light) between the sky and ground (more often around early mornings and late evenings). The sky is naturally brighter than the ground, and oftentimes this will cause problems in obtaining an optimal exposure – most notably blocked shadows (underexposed areas) and blown highlights (overexposed areas) that can not be recovered.  These are highly distracting and can take away much detail from your photo (i.e. great colors and cloud detail in the sky).

Typically, your camera will try and compensate for this disparity and “even out” the difference of exposures between sky and ground – this usually causes your sky to appear washed-out and your ground to appear too dark.

Since your camera can not put two different exposures into one frame – that is, have one exposure set for the brighter sky and another for the darker ground – we need to manipulate how light is entered into the camera.

GND (graduated neutral density) filters act as a literal pair of sunglasses, tinting a certain part of your lens. Part of the filter has an ND (neutral density) effect which will reduce your exposure by a certain amount of stops – in other words, it reduces the amount of light that hits your sensor. The rest of the filter does not have this effect (this is where the “graduated” part comes in) and will have no light-reducing effect.

This filter is fantastic for these types of situations as you typically only need to reduce the exposure for your sky – as seen below.

 

Photo by BenFrantzDale

Since horizon lines are different, GNDs come in two different styles – soft and hard. The soft GNDs have a smooth transition between the tinted glass and the clear glass, which is useful for horizon lines that aren’t smooth – such as those with trees, buildings, etc.

Alternatively, the hard GNDs have very little room for the transition, which work well for those sharp horizon lines – such as a field of snow or where the water meets the sky. It’s a very popular filter for seascape photographers as the ocean’s horizon line is usually flat and unvaried.

So those are GNDs, but what is exposure blending? It’s a process I use often, which is why I wrote an in-depth tutorial on the subject which covers both how to do it and why this process is so important.

If you want the short version – you basically use the same principles applied with the GND filters, but instead take several photos of the same scene at different exposures. Then in Photoshop, you use layers and masks to digitally “blend” the proper exposure for the ground and sky together into one image. It’s the digital version of using a GND.

GNDs and exposure blending are two very different approaches to the same goal: to have an evenly-exposed image with a large tonal range, meaning that your photo has as much detail as possible that hasn’t been lost to improper exposure. There are great benefits to each method – I’ll go over each to help you make a better decision as to what method works best for your photography workflow.

 

Pros of a GND Filter

If you’ve read through my exposure blending tutorial (at least the first part), you know that you’re using three different exposures of the same scene and blending them into one. A drawback to this is what we in the HDR photography world call “ghosting” – which is caused by objects that move within your frame between shots. Things like people walking by, grass blowing in the wind, and waves moving through your scene can all cause ghosting as you blend your images together. Since your layers will be of different opacity, these differences will register as semi-transparent and draw negative attention to your image – as seen below (click for larger version).
 

 
With a GND filter, you’re only taking one photo – not blending different exposures into one – so ghosting is not an issue.

Using a GND filter is also better for long exposures. If you plan on extending your shutter speed for a dramatic effect, it may be time consuming to take three (or more) separate images for your exposure blending. With a GND, you’re working with only one image which can be much easier than going through three.

 

Pros of Exposure Blending

When you’re working with exposure blending, most of your work is done on the computer – which means less work in the field. No additional gear to carry around and set up, and also no additional cost (assuming you’ve already purchased Photoshop).

Exposure blending is much more accurate than using GNDs. Even if you’re selecting the right transition strength for your scene (soft vs. hard GNDs), there’s usually still some elements along your horizon line that won’t look right half-shaded – think of trees or skyscrapers sticking up past your horizon line. With exposure blending, you can use layer masks and draw exactly where you want to change your exposure. You can move between trees, around rocks and other structures along your horizon line with ease – like in the image below. If I used a GND, half of the lifeguard house would be shaded and look unnatural and distracting.
 

 

Even if you use the GND filter, sometimes you’ll have to use exposure blending anyways to get that full tonal range and remove lost detail. A GND reduces the exposure by a fixed amount – and all the scenes we photograph won’t conform to that perfectly. You’ll sometimes find that you may be over/underexposing your scene by a stop or two even with the filter, necessitating the need to bracket your image.

This is especially true for sunsets and sunrises (click here for my guide on how to shoot sunsets). When the sun is in your composition, even the sky itself can have completely different exposure needs that a GND can’t fix. While the sky overall can be exposed perfectly with your chosen GND, the area around the sun can be blown out and lose much detail around its circumference – this is easily reversible by exposure blending an underexposed image just for the sun area.

That is what I did for my image below. I used two different exposures for the sky alone – one for the entire sky, and another exposure taken with a faster shutter speed to blend in the area around the sun. If I didn’t, those dark clouds around the sun wouldn’t be as visible and prominent. If I was using GND filters, this wouldn’t be possible.

 

The Difference in Quality – Which is Better?

A huge issue – or rather question – about whether to use a GND filter or exposure blend is, what is the difference in quality? Which will give me the “better” photo?

The answer is simple – there is no difference.

If both methods are done correctly, you won’t find a difference in quality between a photo taken with a GND filter and one put together in Photoshop by exposure blending. So the key to a high-quality image is not which method you use, but which method can you execute better than the other?

The technique that will give you the “better” photo is the one that you’re most comfortable with. If you’re happy working on your computer and love Photoshop, you’ll be able to blend exposures with great ease. However, if Photoshop is intimidating to you or you don’t have a firm grasp on how to blend layers, you’ll easily become frustrated. If that’s the case, than a GND is probably the better way to go.

If you do decide to go the GND route, landscape photographer Darwin Wiggett uploaded this fantastic video review on the two most popular filter holders for your camera: The Lee Holder and the Cokin Z-Pro Holder. After watching his review, I agree with his points that the Cokin Z-Pro Holder is more practical for the landscape photographer.

I highly recommend B&H Photo Video as your online source for photography gear. The prices are incredible and it’s where I’ve purchased all of my photography needs over the years.

Also, if you click on my B&H link above to purchase your filters or anything else, B&H will give me a donation for my photography gear fund – no cost to you.

 

Which Method Do I Use?

I don’t use GNDs – I exposure blend. That’s not to say one is better than the other, but rather that I enjoy working in the digital dark room and also like the versatility of using masks to selectively decide where I want to adjust my exposure (this is great when working with an uneven horizon line). Of course the downfall to this is potential ghosting – especially if there’s a breeze when I’m photographing, but I’ve learned to work around that.

The point is, there are obvious pros and cons to each method. Don’t choose the one that works the best according to others, but rather the one that works best FOR YOU. If you’re comfortable with your workflow, you’ll find photography much more enjoyable and successful.