Images and Bitmaps (in C#)
Li-Chih Hsu
With a few modifications by Matthew Miling
Advanced Windows Programming
Contents
– Images and Bitmaps
 Fundamental Windows Classes
 System.Drawing.Image
 System.Drawing.Bitmap
 Other Image/Bitmap Types
 Overview
Overview – Images and Bitmaps
 In
computers, two types of graphics
 Vector
- graphics made of lines and curves
- fonts, CAD programs, Photoshop
 Raster
- rectangular arrays called bitmaps
- almost all internet images are bitmaps
Bitmap Support Overview


The System.Drawing namespace has two classes,
named Image and Bitmap.
The Bitmap class and Metafile class are derived from
Image class.
 Bitmap
file formats
A bitmap has a particular height and width measured in pixels.
A bitmap also has a particular color depth,which is the number
of bits per pixel(bpp).
System.Drawing.Image
 Hierarchy
Object
MarshalByRefObject
Image
 Used
to declare an image object:
Image image;
 Used
to load various bitmap formats
.bmp .gif .jpg .png .tiff .exif .wmf .emf
Loading and Drawing
 Three
different methods:
Obtain an image from a bitmap file on disk:
Image.FromFile(string filename)
Obtain an image from a valid bitmap stream
Image.FromStream(System.IO.Stream stream)
Obtain a bitmap object using a Win32 GDI bitmap
Image.FromHbitmap(System.IntPtr hbitmap)
Image Information
Image
Type
Size
int
int
float
float
properties
Property
Accessiblity Description
Size
get
Width
get
Height
get
HorizontalResolution
get In dots per inch
VerticalResolution
get In dots per inch
Drawing the image

Use the OnPaint handler to initiate the draw

Use the DrawImage() method from the
System.Drawing.Graphics class to draw the
actual image

Sample Code
protected override void OnPaint(PaintEventArgs e)
{
e.Graphics.DrawImage(image);
}
Graphics.DrawImage()
 Currently,
30 different instances exist for
the DrawImage() method
 Appropriate method is application specific
void
void
void
void
DrawImage(Image
DrawImage(Image
DrawImage(Image
DrawImage(Image
 Example
1,2
image)
image, int x, int y)
image, int x, int y, int cx, int cy)
image, Rectangle rect)
Metrics vs. Pixels

Images by default draw with metrics for image
device independence



a 3 inch image is 3 inches wide on monitor and printer
relies heavily on embedded resolution (image dpi)
Pixels are a straightforward mapping of bits
onto the screen


One pixel (dot) on screen = one location on bitmap
Image with high dpi will be smaller than image with low dpi,
but will have better visual quality
Rectangular fitting

Shows the different
uses of rectangular
fitting
 Use DrawImage()
with different
arguments for
different effects
 Examples 3, 4
Image Reflection

If we specify a negative width, the image is
flipped around the vertical axis – it’s mirror
image.
 Sample Code:

grfx.DrawImage(image cx/2,cy/2, cxImage,cyImage);
grfx.DrawImage(image cx/2,cy/2, -cxImage,cyImage);
grfx.DrawImage(image cx/2,cy/2, cxImage, -cyImage);
grfx.DrawImage(image cx/2,cy/2, -cxImage,-cyImage);

example5



Rotate and Shear

These two methods effectively
translate,scale,shear,rotate an
image into a parallelogram.

Void DrawImage(Image image, Point[ ]
apt)
 Void DrawImage(Image image, PointF[
] aptf)
 The array argument must contain
exactly three points



Apt[0] = destination of upper left corner of
image.
Apt[1] = destination of upper right corner of
image.
Apt[2] = destination of lower left corner of
image.
See example 6
Partial image display

Ability to draw only a
portion of the image
we would like to see

Let you specify a rectangular
subsection of the bitmap to
display.
Example code:

new Rectangle(0, 0 ,image.Width,
image.Height)
See example 7
Drawing on the image

Ability to overlap text onto the image
 To draw on an image , we need to obtain a
Graphics object that refer to the image.
 Use the DrawString() method
 Cannot use indexed bitmaps! (i.e. gifs)
 Example 8
Thumbnail



The GeThumbnailImage method is intend to be used to create a
thumbnail of an image, which is a smaller version of the image
that an application can use to convey the contents of the image
while saving time and space.


Image GEtThumbnailImage(int cx,int cy,Image
GetThumbnailImageAbort gtia,InPtr pData);
See example 9
System.Drawing.Bitmap
 Derives
from Image
 For applications with images that do
more than just draw
 Allow developer/user to manipulate
graphics at the bit level
 Icons, Animation, Image List, Picturebox
System.Drawing.Bitmap
 Image
has no constructors
 Bitmap has 12 constructors:
 Bitmap(string
strFilename)
 Bitmap(Stream stream)
 Bitmap(Image image)
 Bitmap(Image image, Size size)
 Bitmap(int cx, int cy)
Bitmap Example

Begin with two
bitmaps for text
length
 We see text placed
on a bitmap
 Example 10
 Try different dpi!
Binary Resources

Embed icons and
cursors within the
software

Whenever you create a bitmap,
a cursor,or an icon file you want
to use as resource.
 In visual C#.NET,when you
select any bitmap,icon, or
cursor file in solution Explorer
that is part of a project, you’ll
see a properties window for the
file. Change the Build Action
property to Embedded
Resource.

Example 11
Animation

Uses a Timer data type to load a new
image each tick
 Loads a set of bitmaps into an array for
quick run-through
 See page 530 for ‘Wink’ example
Image List

An image list is essentially just a flexible
array of Image objects with the same
size and color format.
 To create an object:
ImageList imglst = new ImageList();
 To add Image object to the image list:
Imglist.Images.Add(image);
 Number of images in an imageList
imglst.Images.Count;
Image List (cont.)
 To
return to image object
imglst.Images[2];
 ImageList.imageCollection Methods
bool contains(image image)
Int IndexOf(image image)
void RemoveAt(int index)
void Clear()
Image List (cont.)
 Draw
Methods
void Draw(Graphics grfx, Point pt,int index)
void Draw(Graphics grfx, int x, int y,int index)
void Draw(Graphics grfx, int x,int y, int cx,int cy,int
index)
Picture Box

Another image-related control
 Descended from Control
 Properties
Type
image
BorderStyle
PictureBoxSizeMode
property
Accessibility
image
get/set
borderStyle get/set
SizeMode get/set
Question?