Definitions Bitmap and Pixmap
Duration: 7 min
This video lesson is available to enrolled students.
AI Summary
An AI-generated summary of this video lecture.
The video is a lecture on computer graphics, specifically focusing on frame buffers and their representation. It begins by defining a bitmap as a frame buffer in a black-and-white system with one bit per pixel, and a pixmap for systems with multiple bits per pixel. The instructor uses a diagram of a screen to illustrate how a picture is stored in a frame buffer, which is a memory area. The lecture then transitions to a problem-solving section, presenting a question about calculating the refresh rate of a graphic display system. The solution involves calculating the total number of pixels, the total bits in the frame buffer, and the time required to refresh the entire buffer, leading to the final answer of 19 frames per second. The video concludes with a diagram of a computer system architecture, showing the CPU, system memory, frame buffer, video controller, and monitor, and reiterates that the frame buffer stores the picture definition.
Chapters
0:00 – 2:00 00:00-02:00
The video starts with a slide titled 'Bitmap and pix map' which defines a bitmap as the frame buffer in a black-and-white system with one bit per pixel, and a pixmap for systems with multiple bits per pixel. The instructor draws a diagram of a screen, representing a picture, and explains that this picture is stored in a memory area called a frame buffer. The instructor writes 'Picture -> definition' and 'Memory -> frame buffer' to illustrate this concept.
2:00 – 5:00 02:00-05:00
The instructor continues to explain the concept of a frame buffer, writing 'Black & White' and 'bit map' on the screen. A diagram of a screen is shown, with a red dot representing a pixel. The instructor explains that in a black-and-white system, a single bit (0 or 1) is used to represent a pixel. The instructor then draws a small box with a 0 and a 1, labeling it 'bit map'. The instructor also writes '8 bits -> 2^8 = 256 different colors' and '16 bits -> 2^16' to explain how multiple bits per pixel allow for more colors.
5:00 – 7:14 05:00-07:14
The video transitions to a problem-solving section. A question is presented: 'A graphic display system has a frame buffer that is 640 pixels wide, 480 pixels high and 1 bit of colour depth. If the access time for each pixel on the average is 200 nanoseconds, then the refresh rate of this frame buffer is approximately:'. The instructor explains that the size of the frame buffer is calculated as Resolution X bits per pixel. The instructor calculates the total number of pixels (640 x 480 = 307,200) and the total time to refresh the buffer (307,200 x 200 ns = 61,440,000 ns). The refresh rate is then calculated as 1 / (61,440,000 x 10^-9) = 16.27 frames per second, which is approximately 16 frames per second. The instructor then shows a diagram of a computer system with a CPU, system memory, frame buffer, video controller, and monitor, and explains that the frame buffer stores the picture definition.
The lecture provides a comprehensive overview of frame buffers in computer graphics. It starts with the fundamental definitions of bitmap and pixmap, explaining how they relate to the number of bits per pixel. The instructor uses diagrams to illustrate how a picture is stored in a frame buffer, a memory area that holds the intensity values for all screen points. The lesson then applies this knowledge to a practical problem, demonstrating how to calculate the refresh rate of a display system by considering the total number of pixels, the bits per pixel, and the access time. The final part of the video connects the frame buffer to the overall computer system architecture, showing its role in the video display process.