Filters are processes that can be used to change the appearance of an image. There are two main categories of filters: corrective filters, which fine-tune aspects like color and sharpness without drastically altering the image's overall look, and destructive filters, which tend to obscure details and add special effects in a way that makes it obvious a filter was used. Photoshop contains over 100 different filters that are either single-step, applying with no options, or dialog box-based, allowing control over parameters. Smart Filters non-destructively apply effects above an image's original pixel data and can be re-edited or removed.

1.  Image Enhancement using Filter.

2. In This Chapter, you’ll learn on:
 Define what is filters and its main applications

3. What are filters?
 Filters are processes that are used to change the
appearance of an image, layer, channel or
selection in image editing software. You can use
filters to clean up or retouch your photos, apply
special art effects that give your image the
appearance of a sketch or impressionistic painting,
or create unique transformations using distortions
and lighting effects. Filters also called plug-ins
because you can install or uninstall it independently.

4. How Filters work
 All filters do one simple thing in a seemingly
complicated way. Applying a filter is basically same
as giving a set of instructions that tells Photoshop
what to do with a particular pixel in an image or
selection. Photoshop applies these instructions to
each pixel in the relevant area by using a process
the techies call convolution (creating a form or
shape that’s folded or curved in tortuous windings).

5.  Filters got their name from the world of photography, where
you could change how a picture looked by placing a filter over
the lens. The changes can make your photos brighter, redder or
fuzzier. Image enhancement filters can do the same thing, just
with much more variety and control. Most photo editing
program comes with a lot of built-in effects that can make your
image look like everything from a painting to a bad
photocopy.
Original Image Image with Motion Blur filter

6. Types of filters
 Photoshop have more than 14 category and 110
different filters that do many different things. We can
classify filters into two basic categories, corrective
and destructive.
 All corrective and destructive filters are single-step or
Dialog box-based filters.

7. Corrective filters:
 Corrective filters are usually used to correct or fix
problems that you have with the image. They fine-
tune color, add blur, improve sharpness, or remove
such nastiness as dust and scratches.
 Although corrective plug-ins can be fairly destructive
to certain pixels, they don’t change the basic look of
an image in general. You might not even notice that
a corrective filter has been applied unless you
compare the new version of the image with the
original. In corrective filters, pixels are modified, but
the basic appearance of the image remains the
same, albeit hopefully improved.

8.  Some examples of corrective filters are
o Average
o Blur Filters e.g. Gaussian Blur, Lens Blur, Motion Blur,
Radial Blur, Smart Blur:
o Sharpen Filters e.g. Sharpen Edges, Sharpen More,
Un-sharp Mask

9. Destructive filters
 Destructive filters tend to obliterate at least some of
an image’s original detail (some to a greater extent
than others) while they add special effects.
 They may overlay an image with an interesting
texture, move pixels around to create brush strokes,
or distort an image with twists, waves, or zigzags.
 You can often tell at a glance that a destructive filter
has been applied to an image. In destructive filters,
pixels are also modified, but the image will usually
look very different from its original.

10. Destructive filters
Filters range in variety from the corrective (Left), to the destructive (right).

11.  Single-step filters
 The easiest filters to use, single-step filters have no
options and use no dialog boxes. Just select the filter
from the menu and watch it do its stuff on your
image or selection. The basic Blur and Sharpen filters
are single-step filters.
 Dialog box-based filters
 These filters utilize preview windows, buttons, slider controls, and
menus to distort, pixelate, sharpen, stylize, apply textures, and
perform other functions. Most filters come complete with at
least one dialog box, along with (perhaps) a few lists, buttons,
and check boxes. And almost every mini-app filter has sliders
you can use to adjust the intensity of an effect or parameter.

12.  These filters are marked in the menus with an ellipsis (a series of
dots) following their names; like with other menu commands
that show those dots, it’s an indication that you’re about to be
presented with a dialog box where more options are lurking.
Dialog box-based filters act almost like mini-applications.
Example of a dialog box

13.  Smart Filters
 The Filter menu also provides an opportunity to convert for
Smart Filters. If you convert your layer to a Smart Object, you
can then apply a Smart Filter. A Smart Filter is smart because it
doesn’t alter your image pixels, but merely hovers above them,
thereby allowing you to re-edit, or even remove, the filter if
necessary.

 Technically, the filters are applied to your pixel data, but
Photoshop always retains the original pixel data inside the
Smart Object. Then, each time a filter is edited; Photoshop
installs the original pixel data and reapplies the filter. Smart
Filters act like layer effects, appending themselves to your layer,
where they can be edited, rearranged, and deleted at any
time.