Technology ICT Option: Photoshop

Digital Imaging - Photoshop

A digital image is a computer representation of a photograph It is composed of a grid of tiny squares called

pixels

(picture elements) Each pixel has a position on the grid and a colour value These pixels can be

edited

(changing the pixel colours) individually on in groups The illustration below shows an image of a car and a section of it zoomed to show the individual pixels The shape of the pixels is clear as is their positions on the grid making up the digital photograph

Digital Imaging - Photoshop

The

resolution

of an image is the number of pixels it contains This is normally given as dots (pixels) per inch (

dpi

) or dots per centimetre (

dpcm

) The resolution of an image effects its quality -

higher resolution better quality

, but this comes at a price as an increase in resolution means an increase in file size A

doubling

of the resolution produces a

quadrupling

of the file size The chart below shows photographs taken at

150dpi

and

300dpi

The resultant file sizes are shown when the photograph is taken as

black and white

,

grayscale

and

colour

Digital Imaging - Photoshop

Colour models Image editing

software uses colour models to represent the production of colour on the screen and on paper. The main models in use are: •

The RGB Model -

used on computer

monitors

and

projectors

Values ranging from

0

to

255

can be assigned to each of the .

primary colours red, green

and

blue

. These colours are known as the

additive primaries

because if they are combined at full value (

255

), they produce white. If they are combined at values of 0, the resulting colour is black. All other colours are achieved by varying the values assigned to the three primaries

Digital Imaging - Photoshop

•

The CMYK model

- used for

printing

. Based on the colours

cyan

,

magenta

and

yellow

. In theory, pure

cyan

(C),

magenta

(M), and

yellow

(Y) pigments should combine to produce black. For this reason these colours are called

subtractive colours

. Because all printing inks contain impurities, these three inks actually produce a dark brown and must be combined with black (K -

Keystone black

) ink to produce a true black . As it uses percentages for each colour, the values only go to 100 and not 255 as in RGB The subtractive (

CMY

) and additive (

RGB

) colours are

complementary colours

. Each pair of subtractive colours creates an additive colour, and vice versa

Digital Imaging - Photoshop

Graphics formats

Digital images come in two main types: •

Bitmap images -

made up of a grid of pixels. Similar to a mosaic, each pixel has an address and a colour value. As the number of pixels is fixed (

resolution dependant

), these images become jagged when enlarged. Photographs are held as bitmaps because they can display the vast number of colours necessary for photo realism.

Paint

software produces bitmap graphics

Digital Imaging - Photoshop

•

Vector images -

a series of

geometric objects

such as

lines

and

curves

. Each object will have properties such as colour, width, size, fill and position. They are

resolution independent

and can be scaled without any loss of resolution. Photo realism is difficult to achieve with vector graphics and because of this they are rarely used for photographs. They tend to be used in

logo creation

and technical drawings. Their file sizes are considerably smaller than bitmap image files

Digital Imaging - Photoshop

Digital file formats Image editing

software can open and save files in many file formats Some of the file formats are

universal

image editing program and can be produced by any Others are

proprietary

which means they are produced by specific image editing programs (

Photoshop

,

GIMP

etc) The most common

universal

file formats are: •

BMP -

this is the Microsoft graphics format. Images produced using

MS Paint

will be BMP •

TIFF -

these are high quality images. A good digital camera will offer TIFF as it’s best output. It produces images with a large file size and is used in magazines etc •

JPEG -

This is the most common file type created by digital cameras. JPEG images use

lossy compression

. This means that quality of the image is reduces to give a smaller file size

Digital Imaging - Photoshop

•

GIF -

Gif (graphics Interchange Format) files can only display 256 colours in an image compared to 16 million in a TIFF image. Because of this, it is used mainly for logo’s, drawings and diagrams. GIF images can have transparency and this is useful when placing an image on a coloured background •

PNG -

This file format (Portable Network Graphic) was designed as a replacement for GIF. It has the transparency advantage of GIF and can hold a lot more colours making it suitable for photographs

Digital Imaging - Photoshop

The most common

proprietary

file formats are: • • • •

PSD PSP XCF CPT

- these files are produced in

Photoshop

- these files are produced in

Paint Shop Pro

- these files are produced in

GIMP

- these files are produced in

Corel Photo Paint

As these file types are proprietary, they will have special features not available in universal file types For this reason they can usually only be opened in their own programs They must be converted into a universal file format to be used in wordprocessing etc

Digital Imaging - Photoshop

Photoshop -

the industry standard for image editing. It has a comprehensive range of tools and is used by professionals the world over When Photoshop is started, the

Work Area

is blank. This is because the application is mainly used to edit images loaded from camera’s, the Internet etc

Digital Imaging - Photoshop

The Toolbox

The full range of tools are available from the drop down menu, but the most common tools are found in the Toolbox The tools can be broken into categories:

Digital Imaging - Photoshop

The default painting colours in Photoshop are

Black

foreground and

White

background The Toolbox allows these colours to be reversed, or returned to default mode by clicking the relevant controls Some of the tool icons have a black triangle in the lower-right corner. This means that there are more tools of the same kind available on a pop-out menu Each of the tools in Photoshop has it’s own set of options. These appear on a ribbon above the Toolbox when a tool is selected. Below are all the options when the

Text tool

is selected

Digital Imaging - Photoshop

Palettes

help with the editing process. The main ones: •

Swatches -

used to set the foreground and background colours •

Histogram -

shows the spread of the pixels in the image (

Levels

). The pixels will be divided between the

Highlights

on the right of the graph and the

Shadows

on the left and the

Gamma

(mid-tones) in the centre of the graph. A perfect image will show as a bell curve

Digital Imaging - Photoshop

•

Navigator -

used to control the image magnification and the viewing area. Dragging the slider at the bottom of the dialog zooms the image in and out. Dragging the box around the dialog controls the area of the image shown in the workspace. Clicking an area of the image within the dialog moves the rectangle to that area •

History -

the

Undo History

palette keeps a record of all the editing processes carried out on the image. The huge advantage of this is this system is that you can undo any past edit at any time. Normal undo has to be done in the reverse order to the edits

Digital Imaging - Photoshop

Layers -

the

Layers

palette shows all the layers in the image in stacking order. The

Background

layer is at the bottom • • • • • Layers are like a stack of

transparent sheets

Images or paint can be placed on individual sheets and edited without effecting images on other sheets Layers can be dragged up or down the stack Layer display is controlled by toggling the

eye icon

to the left of each layer To edit a layer it must be

active

(highlighted)

Digital Imaging - Photoshop

Opening images

Files in all the universal formats can be opened in the workspace. Depending on the amount of memory in the computer, several images can be open in the editor at the same time To open an image file from the editor: • • • Click the

File

menu and choose

Open.

The

Open

dialog box opens.

Navigate to the folder containing the file Click the file to select it and click the

Open

button

Digital Imaging - Photoshop

Inputting images Scanning digitises

an image so that it can be read, displayed, edited and printed by a computer To scan an image in

Photoshop

: • Click the

File menu

and choose

Import

and select the scanner • Scanning takes place in two stages -

preview

and then

final scan

. The preview scan allows you to select the exact area of the page or photograph you want to scan

Digital Imaging - Photoshop

To do a preview scan: • Click the

preview

button. When the scan is finished, the right hand portion of the scan window will display the preview

Digital Imaging - Photoshop

Before performing the final scan, the software needs to know some information: Firstly, the exact area of the image to be scanned needs to be set. This is done by dragging the

handles

in the preview window Secondly, the

image type

must be set. This can be

colour

,

grayscale

,

black and white

or

custom settings

When all the settings are set, Click

Scan.

The image is scanned into Photoshop and is ready for editing

Digital Imaging - Photoshop

What resolution to use:

The simple formula below can be used to set the scanning resolution:

Example -

An original photograph is

50mm

x

50mm

. It is to be printed at

300dpi

. The photograph is to be scaled to

100mm

x

100mm

in the publication. What resolution should the scanner be set to: Using the above formula:

Answer:

(300/50) x 100 =

600dpi

Digital Imaging - Photoshop

A

Digital Camera

stores pictures electronically on a small internal memory card. The pictures can then be transferred from the card to the computer.

When the camera is connected to the computer, it is seen as a

removable disk drive

and the

Removable Disk

window opens: • Select

Copy Pictures to a folder

and click

OK

Digital Imaging - Photoshop

• The Scanner and camera wizard opens. Click

Next

•

Tick

the required images or choose

Select All

Digital Imaging - Photoshop

• Choose a folder for the images. Tick the

Delete Pictures

box if you want the pictures erased from the memory card • The images are copied to the folder Click

Next

in the following screen and

Finish

Digital Imaging - Photoshop

Alternatively, you can choose

Open folder to view files

in the

Removable Disk

window to control the files as if they were of a disk drive

Digital Imaging - Photoshop

Selecting

Just as text to be edited in a word-processor must be selected, an area of an image or an entire image must be selected if it is to be edited. The main selection tools are: •

Marquee

- the

rectangular

and

elliptical

tools select a defined shape. Select the tool and

drag

the required area. The area is surrounded by marching ants. Hold down the

Shift key

while dragging to constrain the shape to a perfect square or circle

Digital Imaging - Photoshop

•

Polygonal Lasso -

click at intervals along the perimeter of the object to be selected. Press delete to undo the clicks one by one. Hover over the start point until a small circle appears and click to complete the selection •

Magnetic Lasso -

this tool selects highly contrasting edges by allowing the positioning of control nodes around the edges of the image. Click your way around the edges of the object to be selected and join the last point to the first to complete

Digital Imaging - Photoshop

• •

Magic Wand Tool

- this tool selects areas based on colour. Choose the tool and pick a pixel. Set the

tolerance

in the options. This is the variation in shade that will be included in the selection

Path Tool -

select the tool and set the option as shown. Click to create nodes around the perimeter of the object. Join the first and last points to create a path. Select the

Path tab

in the

Layers

palette and click the

small arrow

in the top-right corner to produce a menu. Select the

Make Selection

option and click OK in the dialog box to create the selection

Digital Imaging - Photoshop

Feather

Feathering is necessary when blending images together Standard selections have very hard edges, and when placed in a collage, the sharp edges ruin the realism Feathering a selection creates a soft edge for better blending Feather values are measured in pixels Below is shown the options bar for the rectangular marquee The feather value is set to three pixels which means that a transition area of three pixels exists outside of the selection to blend the image with the area below