Podcast
Questions and Answers
What best describes a raster image?
What best describes a raster image?
Which of the following is a typical format for vector images?
Which of the following is a typical format for vector images?
What do we call the projection of both raster and vector images into a grid of colored elements for display?
What do we call the projection of both raster and vector images into a grid of colored elements for display?
What is the spatial resolution of an image mainly dependent on?
What is the spatial resolution of an image mainly dependent on?
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Which factor affects an image's ability to represent fine details?
Which factor affects an image's ability to represent fine details?
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Why is it recommended to avoid digital zoom for capturing a large image with good detail representation?
Why is it recommended to avoid digital zoom for capturing a large image with good detail representation?
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What does DPI stand for in relation to digital images?
What does DPI stand for in relation to digital images?
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Which file format is NOT typically associated with raster images?
Which file format is NOT typically associated with raster images?
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What is the primary difference between a raster image and a vector image?
What is the primary difference between a raster image and a vector image?
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Study Notes
Image Size and Resolution
- Image size refers to the number of pixels in a digital image, measured in width x height.
- Resolution is the number of pixels per inch (PPI) or dots per inch (DPI), with higher resolution yielding better quality.
Image Size Calculation
- Formula: Total image size = header size + data size
- Data size = width * height * no.of bits/pixel
- Example: 6x4 inch image at 150 PPI, header file size = 10 bytes, total image size = 67510 bytes = 65.92 Kbyte
Gray Scale Image Size Calculation
- Formula: Data size = width * height * 8
- Example: 200x200 pixels, header file size = 80 bytes, total image size = 40080 bytes = 39.14 Kbyte
Color Image Size Calculation
- Formula: Data size = width * height * 3 (for 24-bit color image)
- Example: 400x400 pixels, header file size = 100 bytes, total image size = ?
24-bit Color Images
- Each pixel is represented by three bytes, representing RGB
- Supports 256 x 256 x 256 possible combined colors, or a total of 16,777,216 possible colors
- Stored as 32-bit images, with an extra byte of data for Alpha value representing special effect information (e.g., transparency)
Image Presentation
- Frame buffer: hardware used to store bitmap, typically on a graphics card
- If not enough video card memory, data is shifted around in RAM for display
Digital Image Definition
- Raster image or bitmap: composed of elements that appear when zoomed
- Vector image: does not consist of elements, can be zoomed smoothly
Vector vs. Raster Images
- Raster image: used for photorealistic images, typical formats include JPEG, TIFF, GIF, PNG, etc.
- Vector image: used for simple graphics and drawings, typical formats include EPS, AI, CDR, WMF, DXF, etc.
How We See Digital Images
- Raster and vector images are projected into a raster of colored elements (pixels) when displayed or printed
- Resolution or spatial resolution is the number of pixels per unit of length, usually given as dots per inch (dpi)
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Description
Test your knowledge on calculating image sizes and resolutions. This quiz covers concepts such as the number of pixels in a digital image, pixels per inch (PPI), dots per inch (DPI), and how to calculate binary image sizes based on resolution and dimensions.
