lab6T - Signal Processing First Lab 06: Digital Images: A/D...

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Signal Processing First Lab 06: Digital Images: A/D and D/A Pre-Lab: You should read the Pre-Lab sections of this lab assignment and go over all exercises in the Pre-Lab section before going to your assigned lab session. Verification: The pre-lab section of this lab must be completed before your assigned Lab time to receive credit and the steps marked Instructor Verification must also be signed off during the lab time. One of the laboratory instructors must verify the appropriate steps by signing on the Instructor Verification line. When you have completed a step that requires verification, demonstrate the step to the TA or instructor. Turn in the completed verification sheet to your TA when you leave the lab. Lab Report: Your lab report should cover Sections 2 and 3 with graphs and explanations. You are asked to label the axes of your plots and include a title for every plot. In order to keep track of plots, include your plots inlined within your report. Lab Objective The objective in this lab is to introduce digital images as a second useful signal type. We will show how the A-to-D sampling and the D-to-A reconstruction processes are carried out for digital images. In particular, we will show a commonly used method of image zooming (reconstruction) that gives “poor” results. 1 Pre-Lab 1.1 Digital Images In this lab we introduce digital images as a signal type for studying the effects of sampling, aliasing and reconstruction. An image can be represented as a function x( t 1 , t 2 ) of two continuous variables representing the horizontal ( t 2 ) and vertical ( t 1 ) coordinates of a point in space. 1 Moving images (such as TV) would add a time variable to the two spatial variables. Monochrome images are displayed using black and white and shades of gray, so they are called gray- scale images. In this lab we will consider only sampled gray-scale still images. A sampled gray-scale still image would be represented as a two-dimensional array of numbers of the form x [ m, n ] = x ( mT 1 , nT 2 ); 1 < m < M , and 1 < n < N 1 The variables t 1 and t 2 do not denote time, they represent spatial dimensions. Thus, their units would be inches or some other unit of length.
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where T 1 and T 2 are the sample spacings in the horizontal and vertical directions. In MATLAB,we can represent an image as a matrix, that consists of M rows and N columns. The matrix entry at ( m, n ) is the sample value x [ m, n ]—called a pixel (short for picture element). An important property of light images such as photographs and TV pictures is that their values are always non-negative and finite in magnitude; i.e., 0 < x[m, n] < Xmax < ! This is because light images are formed by measuring the intensity of reflected or emitted light which must always be a positive finite quantity. When stored in a computer or displayed on a monitor, the values of x[m, n] have to be scaled relative to a maximum value X max . Usually an eight-bit integer representation is used. With 8-bit integers, the maximum value (in the computer)
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lab6T - Signal Processing First Lab 06: Digital Images: A/D...

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