Tag: filters

Haida nano pro: a review about the new GND and ND filters

Posted on October 8, 2017 by Isabella Tabacchi

Based in Ningbo, Haida is a company established in 2007, specializing in researching particularly the filters used on the photographic lens, and also other camera accessories.

Haida filters are among the best on the market and one of their best features is the great price-quality evaluation.

And as I’ve tried the new nano-coated products for months, and they survived many travels and extreme environments (like iced rocky beaches, deserts, salted water) I’ve been even more satisfied with the new stuff of the industry from Ningbo.

Here is some image I took with the new Haida filters.

Now to the main characteristics of the products I tested: Nano Pro MC ND 3.0 (1000x) 150×150 and Nano Pro MC Soft GND 0.9 150×170 filters.

The Nano coat

What does “Nano Pro” mean? Well, it’s the extremely thin, nano, a coat which covers the glass surface of the filter.

This is the great innovation of this new product line that makes the difference in comparison to the previous series. It gives resistance to dirt, reflections, and scratches.

Thanks to this coat, my filters fantastically survived sandy, earthy, rocky, icy places.

Furthermore, as a landscaper, I often take shots to waterfalls and rocky beaches where the waves move on the reefs and splash some water on the filter. Thanks to this coat I have just to clean lightly with a towel cause the drops come away very easily.

The holder

You have to put the filters in the grooves of the holder to use them. I own the 150 series holder for my Nikon 14-24mm f/2.8G ED wide-angle lens.

The support system is steel and very steady and resistant. It consists of the universal holder that supports the filters, the front adapter ring and the rear adapter ring that sustain and connect the holder to the lens.

A little gold nut enables to remove or rotate the holder on the rings to position better the filter, especially if it’s a GND.

There are also two rubber plates (superior and inferior) on the holder surface, near the grooves; they prevent the light to come into the space between the lens and the holder, so the nuisance reflections don’t appear on our shots. You can find also some replacement rubber plates in the holder pack.

I also took many very long exposure shots with ND, GND and both filters and I never saw that horrible reflection (similar to crowns) that appear every time the light goes under the filter; so I’m really satisfied with this holder.

The filters

nd filter Haida and Haida

The glass filters are stacked in the grooves of the holder that I described previously.

The sharpness of these filters is excellent and also by the absence of color dominant even if they appear colored at the first sight.

Also, the management of phenomenon like flares and vignetting is great, also because my wide angle already creates some of those.

I also tried to take pictures with GND and ND both mounted and the results are great. But remember to insert the ND always on the first groove nearer the lens to avoid strange light reflections.

Comparisons

Here are following two “with-without” images that consist of not post-processed shots.

In the first, taken in Lanzarote, I used the Nano Pro ND 3.0 (1000x) filter.

You will notice how, in the “WITH” half, the sea water looks like a thick fog and seems velvety. Besides, the clouds are blurred.

comparison nd Haida

In the second, taken in Gran Canaria, I used the Nano Pro Soft GND 0.9 filter.

You will notice how the sky and the upper part of the image are darker, even if the foreground has almost the same brightness and contrast in both the halves. This allows a better managing in postprocessing.

desert Haida

Where can you buy them?

The new Nano Pro filters will be soon buyable in Amazon distributed from Pro-photoshop.

If you live in U.S.A you can visit the HaidaUSA online store.

If you are a Swiss customer, you can also visit the official distributor in Switzerland Fotichaestli.com.

In conclusion…

The quality of the Haida Nano Pro filters is excellent. The strength and the stability of the holder impressed and helped me during my adventures. Even if I often explore extreme and wild locations, my filters are already intact and not damaged.

For instance, I went, as you read, in the desert; there is a lot of sand there; if the glass would be of poor quality, would have a lot of scratches now.

But thanks also to nano coat on it, I was able to clean it without stress.

Many photographers could have some hassles taking shots, for example, to waterfalls. Indeed the water goes frequently splash on the ND filter used on these kinds of shots. But the nano coat permits to clean the glass very easily.

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Must Have Accessories For Landscape Photography

Posted on August 12, 2016 by Kim Suarez

Imagine you’re standing at Glacier Point, shooting the beautiful morning sun as it rises behind Half Dome. Sipping on hot chocolate, you adjust your settings accordingly to the flooding light. The air is wet and there’s a faint vanilla scent from the surrounding Jeffrey Pines. You screw in your Graduated Neutral Density filter and take a couple shots. The sun is rising slow and you are in no rush, savoring each moment you have, just you and the camera this morning. Nothing else matters.

Compare this to someone who ran up, took a shot, and then ran back to their computer for post-processing. They don’t care about crafting the perfect image in the camera, they know they can fix it in post. No hot chocolate for them, no smell of the Jeffrey Pines. No memories other than the photograph.

Where would you rather spend your time? Perfecting the image in camera on location, or spending the majority of your time behind a computer trying to fix the image in post? This answer should not be difficult. What draws photographers to landscape photography is the promise of long afternoons hiking up to the perfect spot and setting up the camera, the sole focus for the next few hours is to get the shot, nothing more.

To ensure you can maintain this lifestyle, you will need a couple accessories in your camera bag. While you can find lists of up to 30 must have accessories, you really just need a few essentials to get started, the rest is up to your creative vision. You cannot buy that, nor can you buy experience. So get out there!

Landscape Photography Filters

Polarizing Filter

A polarizing filter is great for stopping down the entire image. It will reduce glare from reflective surfaces, like water or even from leaves, by stopping down up to 3 stops, depending on which filter you purchase. A polarizing filter will also help to increase saturation in an image. While you may think these are easily replicable in post-processing, there are certain aspects of reducing glare that will be difficult to adjust in Lightroom, requiring more advanced knowledge of the program.

Neutral Density Filter

While you may be able to get away with not carrying a polarizing filter in your bag, a neutral density filter is a must. These filters are offered anywhere from 3-10 stops on average. What’s great about a neutral density filter is it’s ability to block out light, which will allow you to adjust one or more of you camera settings to more of an extreme. You can see this in an image of a waterfall or river, where the water is blurred, the result of a long exposure. The neutral density filter allowed for the slow shutter speed, while still maintaining proper exposure in the image. This is something you could not achieve in post-processing.

Graduated Neutral Density Filter

A graduated neutral density filter works in much the same way as a neutral density filter, but as the name suggests, the filter intensity fades from one end to the other. The purpose of this is for scenes where the sky is too bright when exposed for the landscape. We’ve all seen images like this, where the sky is blown out. Just having a graduated neutral density filter can make the difference between an ok and mind-blowing landscape photograph. While this can be applied in post processing as well, getting it right in camera will ensure the most natural looking image, while allowing for more time in the field and less at your computer. Where would you rather process your image? In front of a beautiful landscape or inside on your computer. Again, not a hard choice to make.

Other Must-Have Accessories

Tripod

An essential accessory for landscape photography, a tripod will allow for those beautiful long exposure shots of star trails and blurred waterfalls. Even if you are shooting a classic landscape image, a tripod is essential to have, in case exposure requires a slow shutter speed. This will happen often, when you want the entire sweeping landscape in focus. The wide aperture requires a slower shutter speed, and increasing ISO introduces more noise into the image. When shooting blurred water to create a dreamy landscape, you’ll need to pair your neutral density filter with a tripod, otherwise there’s no way to achieve this look. When deciding which tripod to get, first confirm what you need. Does it need to be lightweight? Will it get wet? Does it need to hold up heavy lenses? Once you know what you are looking for, then you can narrow down your options and decide which to buy based on price point. There are options at every price point now.

Remote Shutter Release

Pairing well with a tripod, a remote shutter release will ensure there is no camera shake when taking long exposures. Even with a camera on a tripod, the act of pressing the shutter can cause unwanted blur. Remove shutter releases are inexpensive and small, not taking up much space in your bag. It really adds no extra bulk to carry one along with you, you’ll be happy to have it. It could even force you to become more creative with your shooting, trying multiple long exposure options where you normally would shoot handheld. It could add a new dimension to your photography.

While there are more accessories you can carry in your landscape photography, these are the essentials. Don’t get bogged down thinking you need a ton of gear just to get a good image. You can take beautiful photographs without even using the above. The most important is to get out there with what you have and start shooting. Buying more accessories will not make you a better photographer if you don’t know your camera. As your skills grow, so too can your equipment, but for now, keep it simple and enjoy the journey.

Batch-Process Cleverly on Lightroom

Posted on July 21, 2016 by Navanee Viswa

So, remember all those times when you come back home from a shoot with a hundred shots with varied light set-ups? Remember, struggling and pushing to process all those beautiful shots one by one? Will I make your day better if I told you how to cleverly batch-process these images? Maybe, yes.

So, the easiest way to processes your images without consuming too much time would be to split them into batches. When you go for a wedding shoot, or some indoor event, you end up with over hundreds of images in varying light set-ups. So what you can do is split these images into batches of 5 or batches of 10 and apply a setting/edit common to all these selected photographs.

Ideally, a “shoot” indicates that you’ve used various lenses, applied different ISO speed settings, etc. And different images look different depending on the kind of light that got reflected in that moment or depending on the kind of colours that got captured in that particular moment. So how do you cleverly segregate these images into different batches? How do you figure out which ones to group together?

The fundamental idea is to choose a set of photographs where you can apply a group of similar settings. Follow the steps below to make your work progress a lot faster, easier, and a lot more efficient.

Step – 01

Choose a set of photographs (it can range from a set of 4 photographs to almost 20 photographs), this is what we call a “Batch”. Start correcting the first photograph in that set – adjusting Exposure, White Balance, Tint, Tone curve, Sharpness, etc. Remember, you’re going to apply all these settings later to the rest of the batch, so make sure that your corrections will apply similarly for the remaining images as well.

Screenshot 2016-07-19 13.37.35 — The first three images are the ones I’ve combined into a batch for similar processing.

Tip: Do not make major adjustments with the local correction tools, as this might vary from one image to another. What you correct for one image might not apply to the next, even though you’ve grouped them all in the same batch.

Step – 02

The next step is to copy the develop settings from the first photograph, and paste them to the rest of the images in that particular batch. Or alternatively, select the first image, press and hold the ‘Shift’ key and select the remaining photographs. Then, click on the “Sync Settings” button that appears on the lower right bottom of the Library Module.

Batch Processing – Synchronize settings.

Tip: Shortcut to Sync settings is Command + Shift + S

Once you click the sync settings button, a dialog box will open asking about the settings which you would like to copy to the remaining photographs. Make sure that you deselect all the local corrections, and select everything else. Remember, local corrections vary from image to image. So it is advisable to work on the images individually for those changes.

Step – 03

Repeat the above steps 1 and 2, until you are done with all the photographs in the batch.

Step – 04

This is the stage that takes up considerable amount of time. True, it depends on the number of images we’re dealing with and the kind of correction it requires, but this stage also calls for some care and concentration so we don’t go wrong. All the local correction tools namely Crop tool, Adjustment brush tool and Spot removal tool shall be applied manually to each and every photograph in that particular batch. And there we go, you’ve now learned how to speed up your work process while cleverly using the batch process method.Just like how you copy paste the settings from one image to another, you can copy paste noise correction settings as well. The trick is to filter out your images based on a particular ISO setting. Use the filter tool, and filter out images with similar ISO settings. Let’s look at an example. Say, I’m looking for images with an ISO of 1600. Use the filter tool, and filter out all the images in my collection with similar ISO settings. Let’s say Lightroom provides me with a set of 80 images. What do I do no? Pick one image, apply noise-correction changes to this one image, and sync these settings to the remaining 79 images. Tada!

So, use the batch process method effectively, and reduce stress, time-consumption and make your work a lot more fun. We hope this article helped you out, and if yes, let us know about our experience in the comments below.

Local Correction Tools – Lightroom

Posted on July 15, 2016 by Navanee Viswa

Color correction is an art form that relies on your perception, experience, and interpretation of the image. We can do this correction if we have an installed Lightroom presets. The fundamental difference between Global & Local correction tools is simple:Global edits are the enhancements we make to the whole photograph.Global correction does apply the changes across all the pixels in the frame. Global editing shouldn’t be used to correct one part of an image, to the detriment of the remainder.Too often I’ve seen people adjust the white balance of an entire photo to try to achieve “perfect” skin tones. Not only is this quite difficult, it frequently makes the rest of the photo look strange. Good global edits are essential, but they don’t negate the need for local editing. Well-executed local edits are the difference between a nice photo and a great one.Whereas local correction tools apply the changes only based on the areas we choose to apply. Some of the Basic Lightroom tools and Photoshop’s Shadow/Highlight act locally and do not treat all pixels with the same brightness values as identical. Some of the Local correction tools in Lightroom Presets are:
Crop tool(R)
Spot removal tool(Q)
Red eye removal tool
Graduated filter(M)
Radial filter(Shift+M)
Adjustment brush(K)

Local Correction Tools – Toolbar

These tools are available only in develop module and are placed right below the histogram on the right side.

Crop tool ( R)
Crop tool helps us to recompose the photograph that we have taken, to make it aesthetically better or to simply make it more pleasing to the eye. The kind of cropping we do, without a doubt, will vary from one photograph to another. Some might require minor corrections on the horizon while some others might require vertical alignments. Regardless, the crop tool provides the photographer with an opportunity to play around with the proportions, perspective, and the way a photograph looks ultimately. This tool plays a vital role in the post-processing of a photograph.

Click the Develop tab at the top of your workspace. Locate and select the Crop & Straighten tool icon in the toolbar, which opens the options for the tool. Alternatively, press “R” on your keyboard to open the Crop & Straighten tool options.

The Crop & Straighten tools are often the first step many photographers use when editing photos in Lightroom. Use these options to crop a photo for Instagram, straighten crooked photos, or prepare photos for printing.

Crop Tool features

Spot Removal (Q)
In the Develop module, select the Spot Removal tool from the tool strip, or press Q.

The Spot Removal tool in Lightroom lets you repair a selected area of an image by sampling from a different area of the same image. It helps us remove dust speckles, insignificant or unnecessary elements from the photograph, remove skin blemishes, etc. On an advanced level, the spot removal might also help to us to remove certain elements from the photograph, like a person, overhead electrical wiring, etc.
The two spot removal techniques are Clone and Heal.

Heal matches the texture, lighting, and shading of the sampled area to the selected area.
Clone duplicates the sampled area of the image to the selected area.
Spot removal tool – features.

Red eye removal tool
Red Eye will remove the red discoloration of a person or a pet’s eyes that can result from a camera flash going off. Unfortunately, there aren’t any shortcuts available for this particular Lightroom feature, but this is yet another vital tool when it comes to post-processing photographs. To remove a red eye from an eye on a photograph, you can use this tool to remove the red eye and to enhance the eye.
Red-Eye Removal Tool.

Graduated Filter Tool
Graduated filter (M)
In the Develop module, select the Graduated Filter tool from the tool strip, or press M.
The Lightroom Graduated Filter is a versatile tool for making local adjustments to your photos.This tool is a huge help for landscape photo retouch as it can be used to enhance the details from the foreground and the skies.
Radial Filter (Shift + M)
The background or elements surrounding the primary object of your photograph can distract the viewer. To draw attention to the subject, you can create a vignette effect. The Radial Filter tool enables you to create multiple, off-center, vignetted areas to highlight specific portions of a photograph.

In the Develop module, select the Radial Filter tool from the tool strip, or press “Shift + M”.
Radial Filter Tool

Adjustment Brush (K)

The Adjustment Brush tool, literally, works like a brush. The changes or corrections get applied to those regions that you select or brush over. This is one the major advantages of this particular tool – make changes to specific areas or regions of the photograph. The Adjustment Brush tool lets you selectively apply Exposure, Clarity, Brightness, and other adjustments to photos by “painting” them onto the photo.

In the Develop module, select the Adjustment Brush tool from the tool strip, or press K.

The adjustment brush tool combined with the graduated filter tool are a deadly combination. These two tools together have the power to create/produce magical outputs even out of the most simple photographs.

Lightroom is great for processing your photos and understanding how its tools work will help you use it more effectively. Use these features, play around with the tools and tell us about your experience in the comments below. 🙂

5 Useful Filters from Nik Color Efex for Photoshop

Posted on June 13, 2016 by Leonardo Regoli

Even though there are many different image processing software packages out there, for most people, when someone mentions post-processing, the first thing that comes to mind is Photoshop. This is a consequence of the popularity that the program has achieved throughout the years that comes both from a long heritage of users but also from a very powerful set of tools that allow the users to do pretty much whatever they want.

However, sometimes the Photoshop approach to some of the processing techniques is not the most straightforward, and thus different plugins and pre-programmed actions are available out there. While some free options can be found, investing some amount of money can speed up the post-processing workflow to such an extent that, in the end, the initial investment feels insignificant.

One of the most popular plugins out there is Color Efex from the software company Nik. What makes this (and others as well) plugin so attractive is that some complex processing techniques that would normally take several steps in Photoshop only take a single step when using it.

In this post I want to go though five of the most common filters from the Color Efex plugin. For this purpose, I will be using the following image from a lighthouse in Morocco.

B/W Conversion

This particular filter is not that different from making black and white photos in Photoshop. Once the dialog is open, the user can change the filter color, the strength, the brightness and the contrast.

The different parameters give some control over the final image, even though they can as well be adjusted using adjustment layers in Photoshop. However, unless important adjustments are required, the possibility of making changes in Color Efex makes it possible to save some intermediate steps.

Brilliance/Warmth

If there is one basic adjustment that Photoshop could make simpler is the white balance of an image. While there are a couple of native options (Hue/Saturation, Color Balance, Photo Filter), the Brilliance/Warmth filter from Color Efex provides a much more intuitive approach by simply providing a slider where you can turn your image ‘Cooler’ or ‘Warmer’.

The disadvantage is that the tool works for all the colors within the image, but many times this is enough and it saves the user the trial and error involved in other methods.

Darken/Lighten Center

This is Color Efex’s alternative for creating vignettes. While creating a vignette in Photoshop is relatively simple, once again Color Efex provides an easier and more intuitive way of doing it. By providing control over the location of the center of the vignette, its size and the brightness in the brightest and darkest spots, getting the right vignette becomes a very easy task.

Glamour Glow

A quite useful filter for portrait photography, Glamour Glow is a reproduction of the Orton effect. By combining the original image with a blurred version of itself, this filter creates a dreamy look that can enhance both portraits and landscapes alike, when used with care.

Once again, while this can be reproduced in Photoshop in a not so complicated way, Color Efex does a good job wrapping everything up in a single step.

Pro Contrast

This is a very powerful filter that is composed of three individual effects, namely ‘Correct Color Cast’, ‘Correct Contrast’ and ‘Dynamic Contrast’.

The first two have an effect on the global scale, with changes in the color and the contrast all over the image. While these two can be useful sometimes, the third one, ‘Dynamic Contrast’, is probably one of the most useful filters in the whole Color Efex plug in.

What it does is make local adjustments in the contrast of the image, making it possible to obtain a final image with a lot of structure where needed and without adding too much noise in flat areas such as the sky. However, some noise is indeed added, so be careful when using it and, in some occasions, it might be necessary to apply a layer mask to selectively remove the effect in those areas where the noise becomes an issue.

In total, Color Efex has more than 50 filters. I personally find difficult to imagine a situation where some of them could be useful, but others are definitely worth trying. What I showed here are the five that I find the most useful but, as with most things in photography, in the end everything ends up being a matter of personal taste.

Finally, keep in mind that Color Efex is simply one of the many different options that are available in the market, so you might find that some other plugin, actions suite or simply the native tools from Photoshop work best for you.

Behind the Photoshop Filters Masterclass – Sharpening

Posted on April 17, 2016 by Leonardo Regoli

In a previous post, we looked at the mathematical aspects behind one of the basic filters used in image processing, the Gaussian blur. In this post I want to focus on the other basic algorithm that serves as a building block for many of the other post-processing techniques that are usually applied to all kinds of images: the sharpening filter.

It is easy to see sharpening as the opposite of blur. But this does not only hold true for the intuitive aspect but also for the mathematical aspect. While the blur filter is basically a low-pass filter, the sharpening filter is a high-pass filter, meaning that it will leave the high-frequency components more or less unchanged while eliminating or attenuating the low-frequency ones.

High-pass filters are closely related to a technique called edge detection. This is because edges in an image are usually the regions where the high-frequency components are located and thus in order to extract edges, special cases of sharpening filters can be applied.

The technique used to sharpen an image is very similar to the one used to blur it, as it was described in the post dedicated to Gaussian blur and it is based in the convolution of a given matrix (filter) with the image we are applying the filter to. What differs between both techniques is the shape of this filter.

While the filter used for blurring purposes is called Gaussian, the one used for sharpening is called Laplacian. Once again, these filters can be regarded as the opposite of each other. The following figure shows 3D representations of both filters, with the Gaussian on the left and the Laplacian on the right.

If you remember from the previous post, the way the Gaussian filter works at a given pixel is by combining information from the pixel itself and the surrounding pixels, assigning a different ‘weight’ to each of them. By emphasizing the center pixel and combining it with ‘smoothed’ versions of the surrounding pixels, a mixture of information is obtained that ends up producing the blurring effect.

The reason why the Laplacian filter works for sharpening images is because in image processing, sharpness is directly related to edges. This time, by giving more emphasis to the surrounding pixels, the edges of different features are enhanced. In fact, the sharpening filter is a two-step process: first, the edges of the original image are extracted and then, those edges, which correspond to detail information, are added the original image, thus giving a much sharper look.

In reality, once the filtered image is obtained, given the negative sign of the central pixel of the filter, it has to be subtracted from the original image in order to enhance the edges. To see how the process works, let’s take an image with easily recognizable edges on it. Take, for instance, this shot of the Brooklyn Bridge in New York City.

The whole image is full of edges, from the structure itself, to the wooden floor, the painted white lines and the supporting steel structure, so quite a rich output from the Laplacian filter is to be expected.

The following image is the the output of applying the Laplacian filter.

Notice how all the edges within the image are extracted quite neatly while the areas without changes are left out. Finally, as mentioned above, subtracting both images taking care of the image values (the filtering can give negative values that cannot be shown in an image) gives the sharpened result, which is shown in the next image.

If we compare the original image with the final one, it is noticeable how the edges are enhanced while the flat regions like the overcast sky remain unchanged. This is a consequence of the size of the filter applied. For this example, a 3×3 matrix was used and thus no change will be observable for flat regions with a length smaller than 3 pixels and this is the reason why choosing the smallest value for the filter radius in Photoshop will result in smoother images at the end.

If we take, for instance, a 9×9 filter with similar characteristics as the one used for the previous image, the result is a much sharper and noisier image, with a lot of structure on regions that should be rather smooth. The following image shows side by side the output of the Laplacian filter and the filtered image.

In general, when using sharpening filters, always look for the trade-off between getting sharp details where you want them and noise where you don’t. If the areas that you want to leave unaffected are large enough and easily discernible from the rest of the image, it might be easy to apply a layer mask, but if that is not the case, getting the desired results might be just too difficult so the easiest option might be to just reduce the size of your filter.

I hope you enjoyed this second post on post-processing filters and don’t hesitate to write me if you have any question.

Behind the Photoshop Filters Masterclass – Gaussian Blur

Posted on April 8, 2016 by Leonardo Regoli

In this post, I want to start a short series of entries explaining what lies behind some of the post-processing filters that we use on a regular basis with programs like Photoshop or Lightroom. These articles might be a bit technical, but I’ve always found it interesting to know how things work, so I am pretty sure that there are other people out there that will feel the same.

I want to start by looking at a ‘softening’ filter, the Gaussian Blur. This is a filter that, as the name implies, blurs the image (or sections of it) and is often used to reduce the noise of specific regions or when using specific techniques such as frequency separation. But first, let’s see what a filter is in the first place.

Filters

There are many different types of filters, including the ones used for photography when attaching them to the lens to achieve a specific result. The ones I am focusing here are signal processing filters, meaning that they are applied to given ‘signal’. For the specific case of photography, by ‘signal’ we mean the image we are working with.

However, to better illustrate the basic functioning of signal processing filters, it makes sense to look at a simpler example. Images are two-dimensional (2D) in nature, so we will first see what a filter does to a one-dimensional (1D) signal.

The simpler signal one can imagine for this purpose is a sinusoidal signal. This is, for instance, the type of signal that is used to transmit electricity through power lines. The following image shows a sinusoidal image with a frequency of 1 Hz (Hz being an abbreviation for Hertz, meaning ‘cycles per second’).

The frequency is a measure of how many times per second the signal repeats itself. Signal processing filters act upon the so-called frequency components of a given signal, which are the different signals superimposed upon each other, by ‘filtering out’ or eliminating a specific frequency component. Since our simple signal has only one frequency component (1 Hz), it does not make sense to apply any filter, since we will end up with no signal at all.

So let’s complicate our signal by adding another frequency component. This can be achieved in different ways. The following signal was obtained by simply adding a sinusoidal function with a frequency of 10 Hz. What you see now is a superimposition of two frequencies which is actually visible.

The two components in the image above are analogue to the low- and high-frequency components of an image. While the fast changing signal, which completes 10 cycles in 1 second, could be related to an area of large changes (like a brick wall), the slow changing one, completing only 1 cycle in 1 second, could be related to soft clouds on a blue sky.

Now, if we apply a low-pass filter (low-pass meaning that we will let the low frequency components pass and will filter out the high frequency components), what we get in the end is the original signal, simply because we removed the added one. In the example mentioned above, this would be similar to getting rid of any detail on the brick wall while maintaining the soft details on the sky.

Image filters

Image filters work on a similar way but, since as mentioned above images are 2D signals, the filters need to be 2D as well. In a past article, I mentioned that images have, as well, low-frequency and high-frequency components. For this reason, we can also apply a low-pass and a high-pass filter. In this post, I will focus on the low-pass filter, which is the basis of all the blurring filters, being the Gaussian blur one of the most common ones.

The way filters are applied to images is based on a mathematical operation called convolution. Simply put, a convolution is a sequential multiplication of a small matrix (the filter) by a large matrix (the image). Notice that from a mathematical perspective, an image is simply a matrix, as it is the filter, and what the convolution does is multiply both matrices at every possible position, starting from, say, the top left corner and ending at the bottom right corner.

The name Gaussian comes from the function defined by the filter matrix. The following image shows the shape of a 1D Gaussian function.

To illustrate how the convolution works, it is useful to imagine a ‘1D image’ which, for our purposes, will be a line with X values from 1 to 10 and a constant Y value of 1. The X values can be regarded as the pixels of our 1D camera and the Y values the amount of light of our image.

Now try to imagine the result of multiplying the Gaussian function by our image pixel by pixel. Since the maximum value of the Gaussian function is one, it is easy to see that, at the point of the image that coincides with this maximum, the final result will by 1×1 = 1. The rest of the surrounding pixels will acquire the value of the Gaussian curve. This is a simple case because our ‘image’ was formed of ones only.

What is important here is that the Gaussian function gives special importance to a given pixel while it decreases the information contained on the surrounding ones. The particularity of the convolution process is that this is carried out all over the image which, for our 1D case, would mean moving the filter from the position where the maximum peak matches the first pixel until the one where it matches the last one. What we are doing by this process is that, for any given pixel, a special kind of average value of the surrounding pixels is taken into account to obtain the final pixel.

This might sound a bit complicated, but put in different words, what the filter does is include information from the surrounding pixels for all the pixels in the image. And this is why the blurring effect works. What the image processing software (Photoshop, Lightroom, etc.) does is this mixture of information and how much information is going to be mixed is decided by the radius of the filter, a parameter that can usually be adjusted by the user.

The following image shows the effect of a Gaussian blur applied using a self-written code in a programming language called Python.

This post might have not given any useful tip to get better images, but if you are interested in what happens when you click on specific functions of your preferred image processing software, I hope you found this interesting. If you have any question regarding the contents of this post, don’t hesitate to write me an email!

Daylight long exposure – Using ND filters

Posted on February 29, 2016 by Leonardo Regoli

In a recent post, we talked about getting things right when playing with long exposure photography. Today I want to focus on how to get the nice effects that come with long exposure without having to wait until the Sun is already below the horizon. In this article I will be showing you how to get effects like moving clouds or soft-looking water during the day, by means of a specific type of filter called Neutral Density (ND).

Light as we perceive it is formed by a continuum of wavelengths that go from the red to the violet colors, as demonstrated by Isaac Newton back in 1666. If we filter out only one wavelength, we would be left with a picture lacking that specific color. ND filters are designed to equally reduce the intensity of all the wavelengths leaving us, in theory, with a darker version of the original image, without any kind of color cast.

I say ‘in theory’ because so far I haven’t seen any ND filter that does not alter the white balance of the final image. It is true that I might not own the best filter in market, but many people reading this will probably not as well. In any case, the color cast introduced by ND filters is easily removable during post-processing, so don’t get discouraged.

Types of ND filters

ND filters are classified according to the amount of light they block. There are two main scales used and you might find either of them when buying one. One refers directly to the amount of light being blocked (or the inverse of the amount of light that is allowed to reach the sensor of the camera). The other refers to the f-stop numbers that one would have to compensate for in order to get the same final exposure. These two scales are linearly related, so which one will you use is basically a matter of personal taste.

Apart from the classification just mentioned, there are other types of ND filters that differ in nature and have other uses, the most common one being the graduated ND, which is basically what the name says. The ND effect is gradually increased (or decrease, depending on what you choose) in one direction. These filters are usually square and are normally used to correctly expose scenes where the sky is much brighter than the ground (high dynamic range). These were very popular in the times of film photography but nowadays, with the help of post-processing, it is fairly straightforward to deal with this problem, so it is not so common to see someone using on of these anymore.

When and how to use them

As with anything in photography, this is a subjective matter. The obvious answer is: whenever you want to add dynamism to your images. However, there needs to be a dynamic element in order to capture it. For instance, if you are on a cloudless day, no matter how hard you try, you will not get moving clouds in your picture, unless you add them with Photoshop afterwards! So try to think what can be captured moving relatively faster than your subject: clouds, water, passing cars/people, smoke from chimneys, etc.

In terms of how to use them, as with any other filter, you basically stack it in front of your lens and that’s pretty much it. There are two types of filters: screw-on and square filters. Screw-on filters are more comfortable to use and usually produce better images since there is no possibility of reflections coming in from the back of the filter. They are, however, a bit more difficult to deal with when stacking several filters on top of each other.

Another important thing to keep in mind, especially with really dark NDs (e.g. ND1000) is that once you screw it on your lens you will not be able to see anything through the viewfinder. If the scene is not dark yet, you will be able to focus using the Live View mode of your camera but if it is already dark, it will be impossible to focus with the filter on so be prepared to focus before screwing the filter on. For this, you have to be very careful when attaching the filter so that you don’t move the focus ring (unless you are using the newer lenses with the focus ring moved back). Square filters are easier in this sense (it is usually easier to keep the focus while stacking the filters on the holder).

Now that you’ve attached the filter to the lens, you are all set up to take your photo. Apart from what I already said, using a tripod is a must and, as I mentioned in the long exposure post, using the time delay function of your camera (2 s should be enough) is always a good idea to avoid any shake of the camera while taking the photo.

Post-processing

As I mentioned before, most of the times when using ND filters you will notice a color cast towards the red when you open the files on Lightroom or Photoshop. This effect, more prominent for darker filters, is easily corrected if you shoot RAW (always shoot RAW!).

Take, for instance, this image of the Bay Area bridge in San Francisco. The photo was taken at sunset with an ND1000 filter to get a smooth effect on the water.

Right from the beginning, it is evident that a color cast is present, especially on the water. That is where the purple color comes from. Also, if you look more closely, this photo also shows some other problems that arise with the use of ND filters. Since you are exposing for a long time (180 s for this one), some of the problems of your camera that are usually not noticeable will now be. This includes dust in the lens or sensor (small dark spots visible in the sky and the water) as well as damaged pixels in the sensor (visible as very small white or red points visible here on the bottom right corner). Removing them is fairly easy in Photoshop, but we leave that for a future post. For now, let’s take a look at how to get rid of the color cast.

This is also a very straightforward task and the only thing you need to do is open your RAW file in Photoshop.

And this is where you see one of the big advantages of shooting RAW. By playing with the ‘Temperature’ and ‘Tint’ sliders, you will be able to get a more natural look of your scene. That said, sometimes the color cast introduced by the ND filters give a weird but still appealing look so, as usual, it is up to you how much you want to correct for it. What I did for this particular image was to increase the temperature, move the tint slider towards the green (to get rid of the purple on the water) and I additionally increased the contrast and the clarity. This last one provides an extra increase in small scale contrast, something like adding structure to the image.

After doing this and removing the dark and light spots mentioned before, I have my final image. This one has no further post-processing, but you can always enhance different aspects with the versatile tools that Lightroom and Photoshop provide.

And that’s it. If you enjoy long exposure photography, I strongly suggest you give this a try. The simple addition of an ND filter will give your images a completely different mood and I am sure you will enjoy the whole process. If you have any question, please contact me and I will do my best to help you.