Adjusting image sharpness and blur _ Photoshop Tutorial
Sharpening enhances the definition
of edges in an image. Whether your images come from a digital camera
or a scanner, most images can benefit from sharpening. The degree
of sharpening needed varies depending on the quality of the digital
camera or scanner. Keep in mind that sharpening cannot correct a severely
blurred image.
Tips for better sharpening:
Tips for better sharpening:
- Sharpen your image on a separate layer so that you can resharpen it later to output to a different medium.
- If you sharpen your image on a separate layer, set the layer’s blending mode to Luminosity to avoid color shifts along edges.
- Sharpening increases image contrast. If you find that highlights
or shadows are clipped after you sharpen, use the layer blending
controls (if you sharpen a separate layer) to prevent sharpening in
highlights and shadows. See Specify a tonal range for blending layers.
- Reduce image noise before sharpening so that you don’t intensify the noise.
- Sharpen your image multiple times in small amounts. Sharpen the
first time to correct blur caused by capturing your image (scanning it
or taking it with your digital camera). After you’ve color corrected and
sized your image, sharpen it again (or a copy of it) to add the
appropriate amount of sharpening for your output medium.
- If possible, judge your sharpening by outputting it to the final
medium. The amount of sharpening needed varies among output media.
Use the Unsharp Mask (USM) filter or the
Smart Sharpen filter for better control when sharpening your images.
Although Photoshop also has the Sharpen, Sharpen Edges, and Sharpen More
filter options, these filters are automatic and do not provide controls
and options.
You can sharpen your entire image or just a portion using a selection or mask. Because the Unsharp Mask and Smart Sharpen filters can be applied to only one layer at a time, you might need to merge layers or flatten your file to sharpen all image layers in a multilayered file.
You can sharpen your entire image or just a portion using a selection or mask. Because the Unsharp Mask and Smart Sharpen filters can be applied to only one layer at a time, you might need to merge layers or flatten your file to sharpen all image layers in a multilayered file.
Note:
The name Unsharp Mask comes from a darkroom technique
used in traditional film‑based photography. The filter sharpens images
rather than the opposite.
The
Smart Sharpen filter has sharpening controls not available with
the Unsharp Mask filter. You can set the sharpening algorithm or
control the amount of sharpening that occurs in shadow and highlight
areas.
- AmountSets the amount of sharpening. A higher value increases the contrast between edge pixels, giving the appearance of greater sharpness.
RadiusDetermines the number of pixels surrounding the edge pixels affected by the sharpening. The greater the radius value, the wider the edge effects and the more obvious the sharpening.
RemoveSets the sharpening algorithm used to sharpen the image. Gaussian Blur is the method used by the Unsharp Mask filter. Lens Blur detects the edges and detail in an image, and provides finer sharpening of detail and reduced sharpening halos. Motion Blur attempts to reduce the effects of blur due to camera or subject movement. Set the Angle control if you choose Motion Blur.
- Adjust sharpening of dark and light areas using in the Shadow and Highlight tabs. (Click the Advanced button to display the tabs). If the dark or light sharpening halos appear too strong you can reduce them with these controls, which are only available for 8‑bits and 16‑bits-per-channel images:Tonal WidthControls the range of tones in the shadows or highlights that are modified. Move the slider to the left or right to decrease or increase the Tonal Width value. Smaller values restrict the adjustments to only the darker regions for shadow correction and only the lighter regions for highlight correction.
The
Unsharp Mask sharpens an image by increasing contrast along the
edges in an image. The Unsharp Mask does not detect edges in an
image. Instead, it locates pixels that differ in value from surrounding
pixels by the threshold you specify. It then increases the contrast
of neighboring pixels by the amount you specify. So, for neighboring
pixels the lighter pixels get lighter and the darker pixels get
darker.
In addition, you specify the radius of the region to which each pixel is compared. The greater the radius, the larger the edge effects.
In addition, you specify the radius of the region to which each pixel is compared. The greater the radius, the larger the edge effects.
Original image, and Unsharp Mask applied
The degree of sharpening applied to an
image is often a matter of personal choice. Keep in mind that
oversharpening an image produces a halo effect around the edges.
Oversharpening an image produces a halo effect around the edges.
The effects of the Unsharp Mask filter
are more pronounced on‑screen than in high-resolution output. If
your final destination is print, experiment to determine what settings
work best for your image.
- Click the image in the preview window and hold down the mouse to see how the image looks without the sharpening. Drag in the preview window to see different parts of the image, and click + or – to zoom in or out.
- Drag the Radius slider or enter a value to determine the number of pixels surrounding the edge pixels that affect the sharpening. The greater the radius value, the wider the edge effects. And the wider the edge effects, the more obvious the sharpening.The Radius value varies according to the subject matter, the size of the final reproduction, and the output method. For high-resolution images, a Radius value between 1 and 2 is usually recommended. A lower value sharpens only the edge pixels, whereas a higher value sharpens a wider band of pixels. This effect is much less noticeable in print than on‑screen, because a 2‑pixel radius represents a smaller area in a high-resolution printed image.
- Drag the Threshold slider or enter a value to determine how different the sharpened pixels must be from the surrounding area before they are considered edge pixels and sharpened by the filter. For instance, a threshold of 4 affects all pixels that have tonal values that differ by a value of 4 or more, on a scale of 0 to 255. So, if adjacent pixels have tonal values of 128 and 129, they are not affected. To avoid introducing noise or posterization (in images with flesh tones, for example), use an edge mask or try experimenting with Threshold values between 2 and 20. The default Threshold value (0) sharpens all pixels in the image.
If applying Unsharp Mask makes already
bright colors appear overly saturated, choose Edit >
Fade Unsharp Mask and choose Luminosity from the Mode menu.
You can sharpen parts of your image by
using a mask or a selection to prevent sharpening in certain parts of
your image. For example, you can use an edge mask with the Unsharp Mask
filter on a portrait to sharpen the eyes, mouth, nose, and outline of
the head, but not the texture of the skin.
Using an edge mask to apply the Unsharp Mask only to specific features in an image
- Create a mask to apply sharpening selectively. There are many ways to create an edge mask. Use your favorite method, or try this one:
- Open the Channels panel and select the channel that displays the grayscale image with the greatest contrast in the document window. Often, this is the green or the red channel.
Selecting a channel with the greatest contrast
Find Edges filter applied and image inverted- With the inverted image still selected, choose Filter > Other > Maximum. Set the radius to a low number and click OK to thicken the edges and randomize the pixels.
- Choose Filter > Noise > Median. Set the radius to a low number and click OK. This averages the neighboring pixels.
- Choose Image > Adjustment > Levels and set the black point high to get rid of random pixels. If necessary, you can also paint with black to retouch the final edge mask.
Setting the black point high in Levels to eliminate random pixels in the edge maskNote:The Maximum, the Median, and the Gaussian Blur filters soften the edge mask so that the sharpening effects blend better in the final image. Although all three filters are used in this procedure, you can experiment using only one or two.
- With the selection active on the image layer, choose Filter > Sharpen > Unsharp Mask. Set the desired options and click OK.To view your results, select the RGB channel in the Channels panel and deselect the selection in the image.
You can create an action to conveniently apply all the steps in the procedure.
Adds blur to an image to give the effect
of a narrower depth of field so that some objects in the image stay
in focus and others areas are blurred. You can use a simple selection
to determine which areas are blurred, or you can provide a separate
alpha channel depth map to describe exactly how you
want the blur added.
The Lens Blur filter uses the depth map to determine the position of pixels in an image. With a depth map selected, you can also use the crosshair cursor to set the starting point of a given blur. You can use alpha channels and layer masks to create depth maps; black areas in an alpha channel are treated as though they’re at the front of the photo, and white areas are treated as if they’re far in the distance.
The Lens Blur filter uses the depth map to determine the position of pixels in an image. With a depth map selected, you can also use the crosshair cursor to set the starting point of a given blur. You can use alpha channels and layer masks to create depth maps; black areas in an alpha channel are treated as though they’re at the front of the photo, and white areas are treated as if they’re far in the distance.
For a gradual blurring effect (none at the bottom to maximum
at the top), create a new alpha channel and apply a gradient so that the
channel is white at the top of the image and black at the bottom. Then
select the Lens Blur filter and choose the alpha channel from the Source
pop‑up menu. To change the direction of the gradient, select the Invert
check box.
The way the blur appears depends on the
iris shape you choose. The number of blades determines the iris shape.
You can change blades of an iris by curving them (making them more
circular) or rotating them. You can also reduce or magnify the preview
by clicking the minus button or the plus button.
- For Depth Map, choose a source (if you have one) from the Source pop‑up menu. Drag the Blur Focal Distance slider to set the depth at which pixels are in focus. For example, if you set focal distance to 100, pixels at 1 and at 255 are completely blurred, and pixels closer to 100 are blurred less. If you click in the preview image, the Blur Focal Distance slider changes to reflect the clicked location and brings the depth of the clicked location into focus.
- To add noise to an image, choose Uniform or Gaussian. To add noise without affecting color. choose Monochromatic. Drag the Amount slider to increase or decrease noise.Blurring removes film grain and noise from the original image. To make the image look realistic and unretouched, you can return some of the removed noise to the image.
The
Blur tool softens hard edges or reduces detail in an image. The
more you paint over an area with the tool, the blurrier it becomes.
.
The
Sharpen tool increases contrast along edges to increase apparent
sharpness. The more you paint over an area with the tool, the more
sharpening increases.
. (If
the tool isn’t visible, hold down the Blur 
