Siksha Sarovar

Siksha Sarovar (sikshasarovar.com) is a free educational web application that helps students in India learn programming and prepare for academic and competitive exams. The platform offers structured coding courses (C, C++, Python, Java, HTML, CSS, PHP, Power BI, AI, Machine Learning, Data Science), complete university curriculum notes for BCA/MCA students with previous year question papers, Class 10 and Class 12 CBSE/HBSE school notes, and dedicated preparation material for SSC, UPSC, Banking, Railway and other government exams. Browsing the site is completely free and requires no account. Users may optionally sign in with Google solely to save their learning progress, quiz scores and personal preferences across devices.

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Siksha Sarovar is a free e-learning platform for coding courses, BCA university notes and competitive exam preparation. Optional Google sign-in saves your learning progress across devices.

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1.2 Raster vs Random Scan and Display Characteristics

Lesson 3 of 32 in the free Computer Graphics notes on Siksha Sarovar, written by Rohit Jangra.

Two Families of CRT-Era Displays

Although flat panels dominate today, the conceptual distinction between raster and random (vector / calligraphic) scan still shapes how we think about images.

Raster Scan

  • Image is stored as a 2D array of pixels in a framebuffer.
  • Electron beam (or backlight) sweeps left-to-right, top-to-bottom at a fixed refresh rate.
  • Supports filled areas, photographs, complex shading.
  • Suffers from aliasing (staircases) because shapes are sampled at integer pixel centers.

Random Scan (Vector)

  • Stores a display list of geometric primitives (lines, characters).
  • Beam is steered directly along the geometry; no scanning of empty regions.
  • Produces extremely sharp lines, ideal for CAD wireframes.
  • Cannot easily produce shaded solids or photographs.
  • Refresh must be high enough that flicker is invisible; complex scenes can flicker because each line takes time.

Comparison Table

FeatureRasterRandom
StorageFramebuffer (WHbpp bits)Display list (kB)
Image typeAny (photo, shaded)Line drawings
AliasingYes (staircases)No
RefreshConstant timeDepends on complexity
CostCheap, mass producedExpensive, niche

Characteristics of Display Devices

  • Resolution: Number of distinguishable pixels, e.g., 1920x1080. Higher resolution -> finer detail.
  • Refresh Rate: Times per second the entire screen is redrawn (Hz). 60 Hz is baseline; 120/144/240 Hz reduces motion blur.
  • Persistence: Time a phosphor (or pixel) glows after being excited. Low persistence -> less smearing but needs higher refresh; high persistence -> visible ghosting.
  • Aspect Ratio: Width:Height. 4:3 (legacy), 16:9 (HD), 21:9 (ultrawide), 1:1 (square mobile), 16:10 (productivity).
  • Color Depth (bits per pixel, bpp): 1 bpp = monochrome, 8 bpp = 256 colors, 24 bpp = true color (16.7M), 30/36 bpp = HDR / wide gamut.

Quick Calc

A 4K (3840x2160) display at 24 bpp with double buffering needs: 3840 2160 3 * 2 bytes ~= 47.5 MB just for one frame pair, exclusive of depth and stencil buffers.