This document discusses key concepts related to digital image resolution and file size. It covers: - Image size is defined as MxN pixels with k intensity levels, where k=0 for 1 color up to k=8 for 256 colors. Images with 2k levels are called k-bit. - Color images have 3 channels (RGB) with 8 bits each, so a pixel requires 3x8=24 bits or 3 bytes of storage. - Display resolution is measured in megapixels, with over 2 megapixels considered high definition. More pixels at a given screen size increases image quality. - Spatial resolution refers to pixel count, while gray-level resolution depends on bits per pixel

1. Size of the image
Size=MxNxk
When M = N, this equation becomes N2k
Image has 2k intensity levels.
k=0 2k =1 Only one color
k=1 2k =2 Two color [Black & White]
k=2 2k =4 Four color [Black, Dark Gray, Light Gray, White]
k=3 2k =8 Eight color [Black to Gray to White Shades]
When an image can have 2k intensity levels, it is common practice to refer to the image as a
"k-bit image." For example, an image with 256 possible discrete intensity values is called an
8-bit image.
For Color image (RGB)
Three channels
Red channel =8 bit
Green channel =8 bit
Blue channel =8 bit
Memory required to store a single pixel is 224
Resolution
Display Size is 640*480 when worl in VGA monitor (CG Programs)
Total pixels in a screen are 307200
Resolution in Megapixel is 307200/1000000=0.3072 Megapixel
When you say resolution is 5 Megapixel. Pixels on screen are 5000000
When resolution of screen is greater than 2Megapixel it is called High Definition (HD)
As resolution increases that is no of pixels, pixel size becomes small. More number of pixels
in that particular size of the screen. Picture quality enhances.

2. Spatial and Gray Level Resolution
Spatial resolution can be defined as the smallest discernible detail in an image. Spatial
resolution is equal to no. of pixels in an image. It is determined by the sampling process. The
spatial resolution of a digital image reflects the amount of details that one can see in the
image (i.e. the ratio of pixel "area" to the area of the image display). If an image is spatially
sampled at M×N pixels then the larger M×N the finer the observed details.
Measuring spatial resolution:
Since the spatial resolution refers to clarity, so for different devices, different measure has
been made to measure it.
For example:
1. Dots per inch
2. Lines per inch
3. Pixels per inch
Dots per inch: Dots per inch or DPI is usually used in monitors.
Lines per inch: Lines per inch or LPI is usually used in laser printers.
Pixel per inch: Pixel per inch or PPI is measure for different devices such as tablets, Mobile
phones etc.
Gray Level (Tonal) Resolution
Toner : No of color (toner word is used in printer cartridge)
Gray-level resolution refers to the smallest discernible change in gray level. Gray level
resolution is equal to the number of bits per pixel. It is determined by the quantization
process. The number of gray levels is usually an integer power of 2. The most common
number is 8 bits, however, 16 bits is used in some applications where enhancement of
specific gray-level ranges is necessary.
Effect of reducing the gray level resolution
Decreasing the gray-level resolution of a digital image may result in what is known as false
contouring. This effect is caused by the use of an insufficient number of gray levels in
smooth areas of a digital image. To illustrate the false contouring effect, we reduce the

3. number of gray levels of the 256-level image shown in Figure 2.6(a) from 256 to 2. The
resulted images are shown in the figures 2.6(b) through (h). This can be achieved by reducing
the number of bits from k = 7 to k = 1 while keeping the spatial resolution constant at
452x374 pixels. We can clearly see that the 256, 128, and 64level images are visually
identical. However, the 32-level image shown in Figure 2.6(d) has an almost imperceptible
set of very fine ridge like structures in areas of smooth gray levels (particularly in the
skull).False contouring generally is quite visible in images displayed using 16 or less
uniformly spaced gray levels, as the images in Figures 2.6(e) through (h) show.