Adobe Photoshop CS5 for Photographers - Martin Evening [231]
Gaussian Blur
The Gaussian Blur is a good general purpose blur filter and can be used for many purposes from blurring areas of an image to softening the edges of a mask. The Gaussian Blur can sometimes cause banding to appear in an image, which is where it may be useful to use the Noise Add Noise filter afterwards (Figure 10.4).
Figure 10.4 The Noise Add Noise filter can be used to add artificial noise to an image. It is particularly useful whenever you wish to disguise banding that may have been caused through excessive use of the Gaussian Blur filter.
Motion Blur
The Motion Blur filter can be used to create an effective impression of blurred movement. It adds a Linear Blur that spreads in both directions and you can use the filter dialog sliders to control the angle of the blur as well as the distance of the blur spread. In the example that's shown here, I used the Motion Blur filter to add blurred movement to a static photograph of a car.
1.
This shows a photograph of a car that had been cut out and placed as a new layer against a street scene. While the perspective and shadowing may have looked correct, we don't get any sense of movement in this picture.
2.
Next, I converted the Background layer to a Smart Filter layer (essentially a Smart Object), chose Filter Blur Motion Blur and applied a 236 pixel blur at an angle of _3°. This blurred the entire backdrop layer and began to give the impression of movement in the picture.
3.
To get the car movement to look more realistic, I did several more things. I applied a gradient mask to the background Smart Object layer so that the motion blur appeared strongest in the distance. I then duplicated the car cut-out layer and applied a 100 pixel Motion Blur filter. I also duplicated this layer and applied a 400 pixel Motion Blur filter. I moved both layers slightly so that they trailed behind the car, faded the opacity of the softer blur layer and added a layer mask to each so that I could selectively remove some of the motion blur areas. Lastly I selected each of the wheels, copied each one to a new layer, used a Free Transform to make them circular and then used the Spin Radial Blur filter to add circular movement. I then reversed the transform on each layer so that I ended up with a convincing circular spin on each of the wheels.
Surface Blur
This might be considered to be an edge preserving blur filter. The Radius adjustment is identical to that used in the Gaussian Blur filter, so the higher the Radius, the more it blurs the image. Meanwhile, the Threshold slider determines the weighting given to the neighboring pixels and whether these become blurred or not. Basically, as you increase the Threshold this extends the range of pixels (relative to each other) that become blurred. So as you increase the Threshold, the flatter areas of tone are the first to become blurred and the high contrast edges remain less blurred (until you increase the Threshold more).
Box Blur
The Box Blur uses a quite simple algorithm to produce a squareshaped blur. It is a fairly fast filter and is useful for creating quick ‘lens blur’ type effects. It is also useful for creating certain types of special effects. The Box Blur is no match for the power of the Lens Blur filter, but it is nonetheless a versatile and creative tool.
Shape Blur
The Shape Blur filter lets you specify any shape you like as a kernel with which to create a blur effect and you can then adjust the blur Radius accordingly. In Figure 10.5 (bottom image) I selected a lightning bolt shape to simulate a camera shake effect using this filter.
Figure 10.5 This shows from top to bottom, the Surface Blur, Box Blur and Shape Blur filters applied to the same image.
Fade command
Filter effects can be further refined by fading them after you have applied the filter. The Fade command is referred to at various times in the book