Creating an Image Map

By: Mark Lee

January 10, 2008
Download a zip file containing an example

An image map is a picture with clickable regions. Image maps are typically found on WebPages as navigational tools, allowing users to click on pictures or sections of a picture to go to other pages. But, an image map can be used for a lot of other things.

A Few Examples

An image map could be used to simulate irregularly shaped buttons.

Any map could be used to learn geography. The program would ask the user to locate something on the map, and the user would simply click in the right region.

Young kids could learn their body parts by clicking on an image of the human body.

An image map could be used in a point and click type game, such as the popular Nancy Drew series. The player would navigate rooms, pick up objects, dial numbers on a cell phone, etc ... just by clicking the right region of the pictures.

How To Create an Image Map

Create an image with solid colored regions. Bitmaps (Bmps) take up a lot of space, so using high quality Jpegs might be the better option. If you choose to use Jpegs, however, don’t use Microsoft Paint to save the Jpeg. The quality will not be good enough to create an image map. For my image map example, I used Adobe Photoshop Elements to save the Jpegs at the highest quality available.



The next step is to convert the RGB color codes of the solid color regions to single numbers, which are used by windows to read pixel values. I used the following code to do this.

 [begin] 
 input red 
 input green 
 input blue 
 print RGB(red, green, blue) 
 input again$ 
 if again$ = "y" then [begin] 
 end 
 Function RGB(red, green, blue) 
 RGB= red + (green * 256) + (blue * 65536) 
 End Function 

Now, write a program to scan your image, indexing the color of each pixel in the clickable regions. Store this information in a Random Access File database. Colors that are not part of the clickable regions may be ignored or grouped together in a Case Else statment. Here's a code snippet of the scan process.

 'index the pixels 
 PixelNumber = 1 
 for yVar = 0 to 629 'Cycle through the height of the image to be scanned 
 for xVar = 0 to 319 'Cycle through the width of the image to be scanned 
 
 pixelLong = pixelLong(xVar, yVar) 
 
 Select Case pixelLong 
 
 Case 8421504 ' Face 
 
 Part$ = "1" 
 PUT #Body, PixelNumber 
 PixelNumber = PixelNumber + 1 
 
 Case 16711553 ' Neck 
 
 Part$ = "2" 
 PUT #Body, PixelNumber 
 PixelNumber = PixelNumber + 1 
 
 Case 16512 ' Shoulders 
 
 Part$ = "3" 
 PUT #Body, PixelNumber 
 PixelNumber = PixelNumber + 1 
 
 Case 16646144 'Chest 
 
 
 Part$ = "4" 
 PUT #Body, PixelNumber 
 PixelNumber = PixelNumber + 1 
 
 Case 254 ' Arms 
 
 Part$ = "5" 
 PUT #Body, PixelNumber 
 PixelNumber = PixelNumber + 1 
 
 Case 131071 ' Hands 
 
 Part$ = "6" 
 PUT #Body, PixelNumber 
 PixelNumber = PixelNumber + 1 
 
 Case 16711807 ' Stomach 
 
 Part$ = "7" 
 PUT #Body, PixelNumber 
 PixelNumber = PixelNumber + 1 
 
 Case 16744448 ' Hips 
 
 Part$ = "8" 
 PUT #Body, PixelNumber 
 PixelNumber = PixelNumber + 1 
 
 Case 98304 ' Legs 
 
 Part$ = "9" 
 PUT #Body, PixelNumber 
 PixelNumber = PixelNumber + 1 
 
 Case 8388863 ' Feet 
 
 Part$ = "10" 
 PUT #Body, PixelNumber 
 PixelNumber = PixelNumber + 1 
 
 Case Else 'Non Body Part 
 
 Part$ = "0" 
 PUT #Body, PixelNumber 
 PixelNumber = PixelNumber + 1 
 
 End Select 
 
 next xVar 
 next yVar 
 

Such a program may run for several minutes to index large pictures. It took my computer about 8 minutes to index a little more than 200,000 pixels. (That’s a 320 x 630 size image.)

The use of a few API/DLL calls, including the GetPixel function, will be required.

 Function pixelLong(xVar, yVar) 
 
 hGBox = hWnd(#t.box) 
 hDC = hDC(hGBox) 
 
 Open "gdi32"for DLL as #gdi 
 
 CallDLL #gdi, "GetPixel",_ 
 hDC as Ulong,_ 
 xVar as Long,_ 
 yVar as Long,_ 
 pixelLong as Long 
 
 Close #gdi 
 
 CallDLL#user32,"ReleaseDC", _ 
 hGBox as Ulong, _ 
 hDC as Ulong, _ 
 result as Long 
 
 End Function 
 
 
 Function hDC(hGBox) 
 
 Open "user32" for dll as #user 
 CallDLL #user, "GetDC",_ 
 hGBox as Ulong,_ 
 hDC as Ulong 
 
 Close #user 
 
 End Function 

Each clickable region can have a separate picture associated with it. The new picture may replace the old picture when the mouse moves over the region or when a mouse button is either pressed or released. For that matter, a different picture could be triggered with each of the mentioned events. Options at this point are only hindered by your imagination.

The Image Scan program included in the download at the top of this article demonstrates the scan step, and the Image Map program demonstrates using the stored information to simulate an image map.

I would like to thank Alyce for the use of her DLL for viewing jpegs, and I would like to thank Janet for her suggestions and tips.