About Image Editing
Teppo Räisänen
LIIKE/OAMK 2011
What Is Image Editing?
Manipulation of digital images –
from simple operations to
complicated edits
Creation of new images
Image editing has been done
before computers
What Is Image Editing?
Digital image formats can be
divided into
Vector graphics
Bitmap graphics
Vector Graphics
Image is stored in a form of
mathematical algorithms
The image files are typically smaller
than of bitmap images
The images are easily scalable
Best suited for image objects with clear
borders and colors
Vector Graphics
Vector Image Formats
AI Adobe Illustrator
CDR CorelDraw
DRW Micrografx Draw
DXF Autocad
DWG Autocad
EPS Encapsulated PostScript
FH8 Freehand
HGL Hp Graphics Language
PS Postscript
WMF Windows Metafile
Bitmap Graphics
The image file consists of pixel level
color information
Editing a bitmap = affecting to the pixel
color values
Typically bitmaps are used for
photograph editing
scanned images
Scaling upwards will result in lessening
of the image quality
Bitmap Graphics
Bitmap Graphics
The Basic Qualities of Bitmap
Images
Five Basic Qualities:
Pixel Size
Pixel Coordinates
Resolution (ppi)
Color Model (e.g. RGB / CMYK)
Color Depth (bit)
Pixel
• A single pixel is always of matte
color
• Within a single image it’s all pixels
are of same size
• Single pixels should be small
enough not to be observed
separately
• If the pixels are too big =
pixelisation
Resolution
• ppi (=pixels per inch)
• for scanned, self-drawn or digital
camera images
• amount of pixels / inch of an
image
• dpi (=dots per inch)
• the physical accuracy of scanners
and printing devices
RGB
Red, green & blue.
• Three values are stored from each
pixel of the image
• Typical color model of light
emitting devices
• RGB is used for the images of Web
pages
CMYK
cyan, magenta, yellow ja black.
• Color model for printed images
• Editors like Photoshop handle
changes of color models
automatically
• Often colors are set using computer
display (and rgb) and conversion to
cmyk happens only when printing
an image
Bitmap Image Formats
BMP = Windows image format
Large image files
No information about the image’s printing size
can be stored
GIF = CompuServe Graphics Interchange Format
Compressed image format
Used widely for Web graphics
Not good for photographs or images with
gradient colors
GIF can contain animations
Bitmap Image Formats
JPEG, JPG = Joint Phographics Experts Group
Adjustable compression rate
Information about resolution can be saved in the image
file
Used widely for Web graphics
Typical file format of e.g. cameras of mobile phones
PNG = Portable Network Graphics
Developed to be used for Web graphics
Supports transparency
Bitmap Image Formats
PSD = Photoshop format
Information about layers, masking
etc.
Large image files
TIFF = Tagged Image File Format
Compressed/uncompressed
Very large image files
Compatible with many platforms &
applications
Bitmap Image Formats
There are two types of image file
compression algorithms:
Lossless and lossy
Bitmap Image Formats
Lossless compression algorithms
Reduce file size without losing image
quality
Thus images are are not compressed
into as small a file as a lossy
compression file.
When image quality is valued
above file size, lossless algorithms
are typically chosen.
Examples: PNG, TIFF
Bitmap Image Formats
Lossy compression algorithms
Take advantage of the inherent limitations of the
human eye and discard invisible information.
Most lossy compression algorithms allow for
variable quality levels (compression) and as
these levels are increased, file size is reduced.
At the highest compression levels,
image deterioration becomes
noticeable as "compression
artifacting".
Examples: JPG
Rasterizing
= Conversion from a vector shape
to bitmap information
E.g. PhotoShop uses vector shapes
for many operations
To be able to perform some edits
rasterizing is often necessary
Image File Size
• Digital image files may be of
hundreds of megabytes
• Especially Web graphics files
should be small sized
• Eventually the purpose of a file
directs the appropriate file format
and size
Amount of Pixels
Cropping of unused parts of an
image results in faster editing
Resolution
2X resolution = 4X amount of
pixels
Examples of Bitmap
Operations
Contrast optimization
Color balance adjustments
Resizing of an image
Cropping
Rotating and skewing
Blurring and sharpening
Effects (Filters)
Contrast & Color Balance
Red Eye Removal
Cropping & Selecting
Bending (Transformation)
Blurring / Sharpening
Image Content
Manipulation
