Photoshop blur filters are primarily designed to retouch images – to soften, haze, cloud, fuzz or distort specific areas of an image or the entire image. Backgrounds are often blurred to accentuate the main photo or to reduce clutter in the environment. Blur filters also collect and then blend the colors in a selected area to create a specific effect such as movement.
Blur effects explained
When you select Filter> Blur, Photoshop displays a drop-down menu with 11 blur effects. They are defined as follows (and grouped by similarity):
Average: Photoshop takes into account all the colors in a selected area, then calculates the average color of the combined shades and fills the area with that color. When the area is “average”, you can apply additional effects, such as a soft gradient, a simple texture, or a modest pattern to create an unlimited background that does not “compete” with the main subject of the image.
Stain: Use this filter to soften the tagged edges of an object that you “cut out” (using the lasso or the pen tool) from a larger photo. It is also very useful for reducing noise in an image covered with dust particles, scratches, halftone dots or a Moiré pattern from a scanned page. This is a particularly effective solution for an old crumpled or scratched photo that has been scanned.
Blur more: The same result as the blur filter, only increased by four times the effect. The changes are subtle on both blur and blur more, so you may need to “blur more” repeatedly to achieve the desired result.
Box blur & Gaussian blur filter
Box blur: The box blur finds the edges of the objects in an image, and then penetrates the colors of the pixels next to the target objects to create a soft, silky blurred effect. With contrasting colors, Box Blur creates subtle, glowing edges between objects or objects and the background. Use this filter to soften a flower’s petal (see our coral rose in figure 03) and at the same time improve the edges so that the flower stands out against a lively background.
Gaussian blur (or Gaussian distribution) seems to be the most popular. It uses a clock-shaped curve, which has its highest point in the middle, and then decreases on both sides (just like a clock) to blur the selected area in an image. It uses a sliding scale from 0.1 to 1000, which gives a wide result.
Note that the edges of the selected area contain colors from the surrounding areas, which may give a blurred or feathered outline. To avoid this, remove (cut out) the surrounding area first, blur and then paste the surrounding area in place (which is likely to create a hard edge unless you blur the edges of the cut area as well).
In our example (see Figure 04), the client wanted to use a specific photo of a young girl, but he wanted the girl’s identity masked, and the background was a mess. First we changed the Color Balance so that the glasses look like sunglasses.
We used Gaussian blur at a radius of 10 to blur the eye with the glass lens. Then we adjusted the brightness / contrast on the girl’s face to -100 and +40 respectively. And lastly, we adjusted the brightness / contrast of the glass lens to -80 and +50 respectively.
For the recorded background, we adjusted the brightness to -150 and the contrast to +10. Then we used Gaussian blur at a radius of 50 to blur the background enough to show off the girl, while still maintaining a hazy view of the city and the fence behind her. The client loved it!
Lens blur filter & motion blur filter
Lens Blur: Use this filter to adjust the depth of field of your photos – for example, to blur a cluttered background or enhance a blurred background. This powerful filter provides 14 levels of adjustable effects, including six shapes and multiple depth maps. You have more control over the final results of your image because you can fine-tune so many effects.
Check out the red rose in Figure 05. We set the Blur Focal Distance to 100. We used an Octagon shape with a radius of 35, a leaf curve of 55 and a rotation of 25. For the highlights, we did Brightness 10 and Threshold 20. The noise was set to 3 with uniform distribution. The beautiful red rose looks like velvet on a background of green sand.
Motion blur: Motion blur does exactly what you might expect – it creates the illusion of movement. When shooting a moving target, you can “stop” the action with camera settings or set the shutter speed to 1/60th of a second (give or take) and slide the subject “in motion.” With Photoshop, you only use the Motion Blur filter. The settings include the motion angle (from zero to plus or minus 360 degrees) and the distance of the scatter pixels – that is, how far the image is stretched to emulate the motion.
For our example, we used a dancer who jumped through the air (see Figure 06). We chose an angle of 22 degrees, so she seemed to go forward and up. For the distance, we chose 215 pixels, so she would only be blurred enough to copy motion without reducing her image to blurred lines.
Radial blur & shape blur filter
Radial blur: Radial blur is used to create a circular distortion around an object that can be directed or applied to the entire image. Visualize the ripples in a pond around a dropped rock. With this filter you can adjust the amount (or degree) of the blur; the method (spin: along concentric circular lines or zoom: along the radial lines); quality (draft, better, best); and the option to set the blur center.
The most obvious use for radial blur is with circular objects in motion such as the wheels of a tire. For our example, we used the elliptical marking tool to select the tires on this sports car (figure 07). We chose “20” for radial radius, spin (instead of zoom) for blur method and “good” for quality (as opposed to draft or best). Now the car seems to go fast due to the spinning tires.
Shape blur: This effect uses something called an image core, which is basically a two-dimensional matrix of pixels, where each pixel is represented by a number. Based on the image mode (RGB, CMYK, Grayscale, etc.) and the bits per channel (8, 16, 32, etc.), the kernel uses these values to build a new image. Select your core from the shape settings installed on your system, then select a radius value (from 5 to 1000) to blur the image to a shape that loosely matches the preset you selected.
We experimented with several shape presets to see what this blur effect produced. We started with some red chili peppers growing in my garden. We selected the entire image and then selected a music note as the preset shape with a radius of 50 pixels. The effect showed vertical lines that echoed the trunk of the note throughout the image.
Then we chose wavy lines with a radius of 75 pixels. The result was like looking through a cut glass vase or a cross-heated surface, similar to the cross-brush in Photoshop’s Brush Strokes Filter Gallery.
Finally, we chose the hollow cloud preset with a radius of 75 pixels, which produced semicircular blur patterns that resemble a beehive over the surface of the pepper image. The result was a soft, dreamy effect that caused a sleepy response.
Smart blur & surfaces blur filters
Smart blur: This filter uses accurate accuracy based on different pixels, which includes specifying a radius or area size (0.1 to 100); select a threshold (0.1 to 100); and select blur quality (low, medium, high) or blur mode. Modes include Normal (for the entire image), Edge Only, and Overlay Edge (for color transitions, such as black and white edges or white only) to blur images.
For our sample, we chose a light, almost fluorescent color. The challenge was to make this image look like it was air-brushed through a screen, to give it the rough sandpaper look. To achieve this, we chose a Smart Blur Radius of 75 with a threshold of 100. Then we chose Medium Quality and an Overlay Edge. The end product gave a scary, mysterious mask straight out of Voodoo Queen’s wardrobe.
Ytonsuddighet: Unlike Smart Blur, this filter maintains the edges while reducing and smoothing out noise or graininess. The radius determines the area size (1 to 100). The threshold regulates the tone values of the adjacent pixels (2 to 255) and determines how much they must deviate from the center pixel value to be included in the blur effect – or not, if the tone values are less than the threshold value.
Our mannequin is made of spray-painted pyrofoam, so the structure is coarse and grainy like coarse sandpaper. We were commissioned to even out her skin, so she looked more like a black porcelain doll. We used Surface Blur Radius of 20 pixels and a threshold with 55 levels to give her a silky skin that looked more like skin. The client said we succeeded.
There is really no right or wrong way to apply blur effects. The best advice I can offer is to experiment with the 11 different styles until you find one that works for you or your client.
IMPORTANT NOTE: Use the Text tool in Photoshop to take notes on the settings you used for each blur filter. Save the files in a “Filter” folder so you can visit them later when another, similar task pops up.