Post-processing: Selective color

Now that we know how to convert photos to black and white I'm going to show you how to use selective color in your pictures.

Selective color is a very aggresive way to make your subject stand out by converting the rest of the image to black and white.

We're going to learn how to use it in photoshop.

This is the image we'll apply the effect to:



The stones have a very similar color to the background sand and rocks, making them stand out less than I'd like. To solve this we're going to convert all the background to black and white.

First of all we have to select the background, there are many ways to do this but I recommend using quick mask mode (by pressing Q), then going to brush tool and "painting" the stones, like this:

Press Q again to get out of quick mask mode and you'll have the background selected. What I like about this tool, is that using brush makes the edges of your selection soft, allowing some imperfection in your borders. Now you can go to the Channel mixer, like we learned in our previous article and do the black and white conversion.

Remember that the addition of all 3 levers has to be 100% if you want to keep the original luminosity of the image.

And there you've got your selective color effect! Now you can play with contrast, brightness and other options until you've got the image you want. Here's my end result.

Now the stones really stand out against the background, making the image much more interesting

This is another example of selective color

Is there any technique you'd specially like to use? Feel free to post a comment about it!

Understanding Metering modes

In our series of articles about "Mastering the basics" we learned about the different settings to use to get the right exposure, but we never talked about the way we metered available light.

Now, we're going to take a look at the camera's metering modes.

Every modern camera has a sensor that measures how much light is getting through the lens. In most cameras we can chose how we want the camera to do it. There are 3 different metering modes:

Matrix metering: The most used of all modes, the camera measures light from all points in the scene, and attemps to set the exposure in a way that the whole scene is properly lit.
This is a very easy to use and effective metering mode because the largest possible part of the image will be properly exposed. Similarily to the auto mode, though this metering mode has its limitations when we want to have some advanced control over the resulting image.

Center weighted spot metering: This mode comes in very handy when shooting differently lit scenes. Imagine for example, that you're shooting at a concert. The whole scene is dark, except for the performer in who is lit by spotlights. Using the matrix mode, the camera will try to expose the biggest part of the scene, as a result the preeminent darker zones will be properly exposed, while the performer will be overexposed. This will be in many cases far from the ideal result. In these situations we'll use the center weighted metering mode, now the camera will prioritize the area in the middle and expose properly for a portion of approximately 25% of the image around its center.

Photo by sint

Central spot metering: This is the most selective mode, the camera will expose properly for a point situated in the exact center of the image. The rest of the scene will not be taken into consideration. I do not recommend this mode in most of the cases because light can change a lot from one point to another and the readings won't be very useful if we use one point only. It can be a good mode to use if we want to select an exact point for the camera to expose properly though which can be useful for example for creating silhouettes or for complicated light situations.

Now, when you read about the last two metering modes you were probably asking yourself, what about the framing? What if I want the performer in the concert to be properly exposed, without framing him in the middle?

Well, camera designers were aware of this problem and that's what the Auto Exposure Lock button is for. Most DSLRs have this button that allows you to lock the exposure settings once your camera has taken the light readings and adjusted its settings accordingly. This will allow you to take the light readings from the performer by placing him in the center and then, with the AE-Lock button pushed frame the shot as you want to.

Summing up: Center weightered and center spot metering modes, allow you to chose the part of the image you want to be correctly exposed, while matrix metering mode will try to have the whole image exposed properly.

Mastering the Basics: Understanding Aperture

After having learned about shutter speed and ISO settings, now we're going to take a look at the aperture.

The aperture setting is the size of the opening in the lens.

Every lens has a couple of blades, called iris, that are put together to regulate the light that gets through, depending on the aperture setting used.

The aperture is indicated in the camera as the f number. A high f number will represent a small aperture while a small f number will represent a big one. This might sound counterintuitive but is easier to understand if we imagine the f number in the formula 1/f. The higher the f number the smaller the end result.

But enough with the technical details, what is aperture good for?

Tweaking the aperture settings will not only control the light intake, but will also control the size of the depth of field (In short, the depth of field is the part of the image that is in focus). This will allow us to use the depth of field that we find appropiate for our shot. Imagine for example that we are taking a portrait picture. We want everything in the background to be out of focus, so that it doesn't distract from the main subject. In order to achieve that we will use a small f number, that will result in a big aperture, creating a shallow depth of field.
If we were shooting a landscape for example we would do the exact opposite so that all the parts of the image stayed in focus.

The maximum aperture setting will depend from each lens and is an important factor to have in mind when buying new gear, prime lenses, those without zooming possibilities, are the ones which allow higher apertures. It is easy to find cheap prime lenses allowing for f1.8 apertures and more expensive ones even allow for f1.4 or f1.2. Zooming lenses instead have smaller apertures and their maximum aperture varies depending on the focal length used. The 18-55mm kit lens from the D40 for example will allow for a f3.5 aperture at 18mm but only f5.6 at 55mm. Zooming lenses with bigger apertures are only found in the professional level and are used by sport photographers for being able to capture fast shots even in low light.

Summing up, rising the aperture setting will let in more light while making the depth of field smaller and the maximum aperture depends on the type and the quality of the lens.

Mastering the Basics: Understanding ISO

In the last article about the exposure triangle we took an in-depth look at the shutter speed and we mentioned how sometimes it was better to use a slow shutter speed than a high ISO. Now we're going to analyze why this happens.

First of all what is the ISO setting?

The ISO setting represents the sensors sensitivity to light.

Getting into more technical details, the ISO setting in digital photography is the gain of the sensor's signal. Although we speak about digital photography the camera's sensor itself is an analog device, just like a microphone for example, and as such its signal can be amplified to get more light into the picture.

This can be useful because it will allow us to use a faster shutter speed or smaller aperture when we need it (see article about shutter speed), but amplifying the signal will create noise, which will translate into small color dots in our image like in this example photograph. Depending on the camera and the ISO setting this noise can go from slightly visible to spoiling our image. Most modern DSLRs will be able to handle noise from ISO 200 to 800 at acceptable noise rates, but it's always a good idea to keep ISO at its minimum and only rise it when the we're forced to.
As an example a typical situation where you're forced to rise the ISO is at concert photography, where there is dim light and you can't use slow shutter speed because the subject would be blurred, in that case you can only rise the ISO, although you know you will have an image with some noticeable noise.

Summing up all you need to know about ISO is that you have to keep it as low as you can by using, when possible a slow shutter speed or a big aperture.

Mastering the Basics: Understanding shutter speed

In my last article I mentioned how tweaking every setting to get the correct exposure had it's pros and cons. The first setting we're going to take a look at is Shutter speed.

The Shutter speed is the amount of time that the camera's sensor is exposed to light.

This simple setting has a great impact on the end result of the photograph. Using a fast shutter speed will freeze the moment, while a slow one will capture motion in the shot.
Keeping this in mind is very important because we will need to change this setting often depending on the type of photography we're doing. A classic example for this is sports photography. At sports events we're often photographying fast moving subjects, so we will need to set a fast shutter speed to capture the moment.
Sometimes though we will want the photograph to show the movement in the scene. Using a slow shutter speed moving objects will be blurred giving the viewer a sense of speed.

The problem with slow shutter speeds is that it's difficult to hold the camera completely still, so at certain speeds the whole photography will become blurred.

Sometimes we will need to use a slow shutter speed because there isn't enough light available even when rising the ISO and aperture. When this is the case it is very useful to use a tripod that will allow us to have the camera completely still during the exposure of the shot. Using a tripod will also allow us to use very long shutter speed to create interesting effects like light or star trails, which we will talk about in further articles.