Presentation by Dr Jimmy Lan.

1. Computer Image
Dr Jimmy Lam
CAD for Fashion and Textiles

2. Working with bitmap images and
vector graphics
Computer graphics fall into two main
categories--bitmap and vector.
You can work with both types of graphics
in Photoshop and ImageReady
Understanding the difference between
the two categories helps as you create,
edit, and import artwork

3. About bitmap images
 Bitmap images--technically called raster
images--are made up of a grid of dots known
as pixels. When working with bitmap images,
you edit pixels rather than objects or shapes.
Bitmap images are the most common
electronic medium for continuous-tone images,
such as photographs or digital paintings,
because they can represent subtle gradations
of shades and color

4. About bitmap images 2
 Bitmap images can lose detail
when scaled on-screen
because they are resolution-
dependent, they contain a
fixed number of pixels, and
each pixel is assigned a
specific location and color
value. Bitmapped images can
look jagged if they're printed at
too low a resolution because
the size of each pixel is
increased.

5. About vector graphics
Vector graphics are made up of
mathematically defined lines and curves
called vectors. This means that you can
move, resize, or change the color of a
line without losing the quality of the
graphic

6. About vector graphics 2
 Vector graphics are resolution-
independent--that is, they can
be scaled to any size and
printed at any resolution
without losing detail or clarity.
As a result, vector graphics are
the best choice for
representing bold graphics that
must retain crisp lines when
scaled to various sizes (logos,
for example).

7. Understanding image size and resolution
 Understanding the relationship between the pixel
dimension of an image and its print resolution is key to
producing high-quality images.
 The amount of detail in an image depends on its pixel
dimensions, while the image resolution controls how
much space the pixels are printed over. For example,
you can modify an image's resolution without changing
the actual pixel data in the image--all you change is
the printed size of the image. However, if you want to
maintain the same output dimensions, changing the
image's resolution requires a change in the total
number of pixels

8.  Pixel dimensions equal document (output) size
times resolution
 A. Decreasing the resolution without changing
pixel dimensions (no resampling)
 B. Original dimensions and resolution
 C. Decreasing the resolution at same
document size decreases pixel dimensions
(resampling)

9. Pixel dimensions and image
resolution
 The number of pixels along the height and
width of a bitmap image is called the pixel
dimensions of an image.
 The resolution of an image is determined by
the number of pixels per inch (ppi) printed on a
page. In Photoshop, you can change the
resolution of an image. In ImageReady, the
resolution of images is always 72 ppi, to
optimize the images for online media

10. Pixel dimensions and image
resolution 2
 When printed, an image with a high
resolution contains more, and therefore
smaller, pixels than an image with a low
resolution. Higher-resolution images can
reproduce more detail and subtler color
transitions than lower-resolution images
because of the density of the pixels in the
images. High-quality images often look good
at any print size.
 You can't improve a lower-quality image by
printing it at a high resolution. Changing the
print resolution of an image simply makes
each pixel larger, which results in
pixelation--output with large, coarse-looking
pixels. Increasing the print resolution of an
image doesn't add any pixel information to
the image. You can make a low-resolution
image look its best by picking a print size
that makes the most of the pixels it has.

11. Pixel dimensions and image
resolution 3
It's important to note
that video files are
displayed only at 72
ppi. Even if an image
has a higher resolution
than 72 ppi, when it's
displayed in a video
editing application, the
quality may not look
very good.
Printing the same low-resolution
image at different sizes
A. Small print size
B. Medium print size
C. Large print size

12. Printer resolution
 Printer resolution is measured by the number of ink
dots per inch (dpi) produced by all laser printers,
including imagesetters. (See
Preparing images for press).
 Inkjet printers produce a microscopic spray of ink, not
actual dots; however, most inkjet printers have an
approximate resolution of 300 to 720 dpi (see
Printing images to a desktop printer). Many inkjet
printer drivers offer simplified print settings for
choosing higher quality printing. To determine your
printer's optimal resolution, check your printer
documentation

13. Monitor resolution
 Image data are translated directly into monitor
pixels. This means that when the image
resolution is higher than the monitor
resolution, the image appears larger on-screen
than its specified print dimensions.
 Monitor resolution depends on the size of the
monitor plus its pixel setting. For example, a
large image (800-by-600-pixel dimension)
shown on a 15-inch monitor would almost fill
the screen, but on a larger monitor, the same
image would take up less room on the screen,
and each pixel would appear larger

14. Monitor resolution 2
 When you are preparing
an image for online
display, pixel dimensions
become especially
important. You should
make sure that the size of
an image allows room for
the Web browser window
controls on smaller
monitors

15. Changing image size and resolution
 Once you have scanned or imported an image, you may want to
adjust its size. In Photoshop, the Image Size dialog box lets you
adjust the pixel dimensions, print dimensions, and resolution of
an image; in ImageReady, you can adjust only the pixel
dimensions of an image.
 For assistance with resizing and resampling images in
Photoshop, choose Help > Resize Image. This interactive wizard
helps you scale your images for print or online media.
 Keep in mind that bitmap and vector data can produce different
results when you resize an image. Bitmap data is resolution-
dependent; therefore, changing the pixel dimensions of a bitmap
image can cause a loss in image quality and sharpness. In
contrast, vector data is resolution-independent; you can resize it
without losing its crisp edges

16. Discussion
What is the different between bit-
mapped image and vector image?
What are the relationships between file
image sizes, screen image sizes and
printer images sizes?