 Lecture 4

Image Resolution  The resolution of an image is the number of pixels per unit length (pixels/inch or pixels/cm).  You must change either resolution or size option but resampling must be applied for most projects.  In an image manipulation software such as Photoshop, in order to change the size without changing the resolution, or vice versa, you must tick Resample Image in the Image Size dialogue. 2

Controlling the Size of Images  Downsampling means “reducing the pixel dimension” and increasing the pixel dimensions means “upsampling”.  Downsampling and upsampling always result in loss of image information. 3

Controlling Size of Images cont.  You can change the size of an image while optimizing it for the Web in Photoshop.  An image’s colour mode determines how colour values are stored, and may limit the range of colours in the image.  Images intended for display on a computer monitor and for use on the Web should be in RGB colour.  In Photoshop, use the Image>Mode sub-menu to change the colour mode if necessary. 4

Importing from External Devices  Photoshop can import images directly from various external devices.  Importing from external devices directly into Photoshop is achieved through the use of plug-ins.  These plug-ins are not supplied as part of Photoshop, but must be obtained from the device’s manufacturer and must be installed according to their instructions. 5

Plug-ins in Photoshop  The name of any plug-in of this sort that has been installed will appear in the File>Import sub-menu in Photoshop.  Depending on the scanner’s manufacturer and its quality, a range of facilities may be available from within a plug-in interface.  There will certainly be a means of previewing the scan, and you can usually select just part of the image to import. 6

Plug-ins in Photoshop cont.  Colour adjustments and sharpening are easy to do when the photo file has been imported into the Photoshop.  If you notice the term “adjustments” has been used often in this lecture; this is because, this week, we are going to learn about “photo filters and adjustment” and “the photo filters are actually adjustments” 7

What is image manipulation software?  Image manipulation software provides high-level operations for systematically altering pixels.  Most operations are described by analogy with traditional photographic techniques, such as the use of masks and filters. 8

Which software to use ?  There are many options for choosing the right software for your projects; Photoshop is the de facto industry standard; Gimp is an Open Source alternative. Image Magick can be used for command-line processing.  Using the correct software, Bitmapped images can be manipulated easily. 9

Photoshop and its use in the IT Industry  Examples of tasks that you might use to manipulate images:  Removing a colour cast (that is, an unnatural predominance of one colour) from a photograph or scanned image.  Sharpening up a blurry or badly focused image.  Compensating for bad exposure in an original photograph. 10

Photoshop and its use in the IT Industry con.  Removing unwanted background objects from a photograph.  Superimposing type on a picture and altering its appearance, for example to give it a 3D bevelled look.  Creating a collage from a mixture of scanned images, graphics created in some other programme and still images taken from digitized video footage. 11

Photoshop and its use in the IT Industry cont.  Increasing the contrast of a screenshot to make the text more legible.  Changing the resolution of a scanned image from 600 dpi to 72 dpi for display on a monitor.  Optimizing an image for display on a Web site, where you need to compromise between image quality and file size; or creating animation.  You must remember that you may have to combine many operations on an image in order to obtain the effects you want/need. 12

Layers and their importance  Images are often organized into layers, which are like overlaid sheets that may have transparent areas.  Layers are used for compositing or experimenting with different versions of an image.  Areas may be selected by drawing with marquee and lasso tools or a Bézier pen, or selected on the basis of colour similarity or edges using a magic wand or magnetic lasso. 13

Use of Filters in Photoshop  Filters are used for changing the values of pixels in an image.  Filters automate the techniques that are used in the traditional photographic dark room.  A filter can alter every pixel in an image, and some filters perform complex calculations using the values of several neighbouring pixels.  Filters must be applied to selected pixels. 14

Filters cont.  Applying a filter may take some time and you must use the filters cautiously.  Filters can be applied to a selection or a layer by selecting the options from the Filter menu’s sub- menus.  Some filters have no parameters or their own special dialogue, but most can be applied through the filter gallery. 15

Filters cont.  If the filters are applied with no variable parameters, there is no need to set any values and the filter can be applied immediately.  These filters are easy to identify by the absence of an ellipsis (…) after their name in the menu.  Examples include Facet and Fragment on the Filter>Pixelate sub-menu, and Blur and Blur More on the Filter>Blur sub-menu. 16

Filters cont.  Many more useful filters have their own dialogue boxes.  With the dialogue boxes various parameters controlling the extent of the alterations which the filter produces can be changed. 17

How to control filters?  Parameters are controlled by sliders or rotating dials (for setting angles).  The effect of the controls can be controlled easily.  The effect of all filters with parameters can be previewed – they have a detailed preview within the dialogue box itself. 18 A Filter Dialogue

THANK YOU 19