Transcript Slide 1
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