1. Images and Bitmaps (in C#)
Li-Chih Hsu
With a few modifications by Matthew Miling
Advanced Windows Programming

2. Contents Overview – Images and Bitmaps Fundamental Windows Classes
System.Drawing.Image
System.Drawing.Bitmap
Other Image/Bitmap Types

3. 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

4. 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).

5. 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

6. 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)

7. Image Information Image properties
Type Property Accessiblity Description
Size Size get
int Width get
int Height get
float HorizontalResolution get In dots per inch
float VerticalResolution get In dots per inch

8. 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); }

9. Graphics.DrawImage()
Currently, 30 different instances exist for the DrawImage() method
Appropriate method is application specific
void DrawImage(Image image) void DrawImage(Image image, int x, int y) void DrawImage(Image image, int x, int y, int cx, int cy) void DrawImage(Image image, Rectangle rect)
Example 1,2

10. 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

11. Rectangular fitting Shows the different uses of rectangular fitting
Use DrawImage() with different arguments for different effects
Examples 3, 4

12. 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

13. 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

14. 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

15. 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

16. 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

17. 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

18. 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)

19. Bitmap Example Begin with two bitmaps for text length
We see text placed on a bitmap
Example 10
Try different dpi!

20. 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

21. 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

22. 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;

23. 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()

24. 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)

25. Picture Box Another image-related control Descended from Control
Properties
Type property Accessibility
image image get/set
BorderStyle borderStyle get/set
PictureBoxSizeMode SizeMode get/set

26. Question?