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To accomplish this, we will need to take advantage of the IDM by initializing the input and output streams. At the start ofthe function, two instantiations of a new structure dstr_t are declared. You can view the structure contents of dstr_t on p. 2-11 of the IDK Programmer's Guide . The structure contents are defined with calls to dstr_open() . This data flow for the pre-scale is shown in data flow .

Data flow of input and output streams.

To give you a better understanding of how these streams are created, let's analyze the parameters passed in the first callto dstr_open() :

External address: in_image->data

This is a pointer to the place in memory serving as the source of our input data (it's the source because the lastfunction parameter is set to DSTR_INPUT ).

External size: (rows + num_lines) * cols = (240 + 2) * 640

This is the total size of our input data. We will only be taking every other line from in_image->data , so only 240 rows. The extra two rows are for buffer.

Internal address: int_mem

This is a pointer to an 8x640 lexographic array, specifically scratchpad->int_data . This is where we will be putting the data on each call to dstr_get() .

Internal size: 2 * num_lines * cols = 2 * 2 * 640

The size of space available for data to be input into int_mem from in_image->data . Because double buffering is used, num_lines is set to 2.

Number of bytes/line: cols = 640, number of lines: num_lines = 2

Each time dstr_get() is called, it will return a pointer to 2 lines of data, 640 bytes inlength.

External memory increment/line: stride*cols = 1*640

Left as an exercise.

Window size: 1 for double buffered

The need for the window size is not really apparent here. It will become apparent when we do the 3x3 blockconvolution. Then, the window size will be set to 3. This tells the IDM to send a pointer to 3 lines of data when dstr_get() is called, but only increment the stream's internal pointer by 1 (instead of 3) the next time dstr_get() is called. This is not a parameter when setting up an output stream.

Direction of input: dstr_input

Sets the direction of data flow. If it had been set to DSTR_OUTPUT (as done in the next call to dstr_open() ), we would be setting the data to flow from the Internal Address to the External Address.

Once our data streams are setup, we can begin processing by calling the component function pre_scale() (in pre_scale.c ) to operate on one block of data at a time. This function will perform the horizontal scaling byaveraging every two pixels. This algorithm operates on four pixels at a time. The entire function is iterated within pre_scale_image() 120 times, which is the number of rows in each quadrant. Before pre_scale_image() exits, the data streams are closed, and one line is added to the top and bottom of theimage to provide context necessary for the next processing steps. Now that the input image has been scaled to a quarterof its initial size, we will proceed with the four image processing algorithms. In img_proc.c , the set_ptr() function is called to set the variable out_ptr to point to the correct quadrant on the 640x480 output image. Then copy_image() , copy_image.c , is called, performing a direct copy of the scaled input image into the lower right quadrant of theoutput.

Questions & Answers

what is math number
Tric Reply
x-2y+3z=-3 2x-y+z=7 -x+3y-z=6
Sidiki Reply
Need help solving this problem (2/7)^-2
Simone Reply
what is the coefficient of -4×
Mehri Reply
the operation * is x * y =x + y/ 1+(x × y) show if the operation is commutative if x × y is not equal to -1
Alfred Reply
An investment account was opened with an initial deposit of $9,600 and earns 7.4% interest, compounded continuously. How much will the account be worth after 15 years?
Kala Reply
lim x to infinity e^1-e^-1/log(1+x)
given eccentricity and a point find the equiation
Moses Reply
12, 17, 22.... 25th term
Alexandra Reply
12, 17, 22.... 25th term
College algebra is really hard?
Shirleen Reply
Absolutely, for me. My problems with math started in First grade...involving a nun Sister Anastasia, bad vision, talking & getting expelled from Catholic school. When it comes to math I just can't focus and all I can hear is our family silverware banging and clanging on the pink Formica table.
I'm 13 and I understand it great
I am 1 year old but I can do it! 1+1=2 proof very hard for me though.
Not really they are just easy concepts which can be understood if you have great basics. I am 14 I understood them easily.
hi vedant can u help me with some assignments
find the 15th term of the geometric sequince whose first is 18 and last term of 387
Jerwin Reply
I know this work
The given of f(x=x-2. then what is the value of this f(3) 5f(x+1)
virgelyn Reply
hmm well what is the answer
If f(x) = x-2 then, f(3) when 5f(x+1) 5((3-2)+1) 5(1+1) 5(2) 10
how do they get the third part x = (32)5/4
kinnecy Reply
make 5/4 into a mixed number, make that a decimal, and then multiply 32 by the decimal 5/4 turns out to be
can someone help me with some logarithmic and exponential equations.
Jeffrey Reply
sure. what is your question?
okay, so you have 6 raised to the power of 2. what is that part of your answer
I don't understand what the A with approx sign and the boxed x mean
it think it's written 20/(X-6)^2 so it's 20 divided by X-6 squared
I'm not sure why it wrote it the other way
I got X =-6
ok. so take the square root of both sides, now you have plus or minus the square root of 20= x-6
oops. ignore that.
so you not have an equal sign anywhere in the original equation?
is it a question of log
I rally confuse this number And equations too I need exactly help
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Commplementary angles
Idrissa Reply
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salut. from Algeria
A soccer field is a rectangle 130 meters wide and 110 meters long. The coach asks players to run from one corner to the other corner diagonally across. What is that distance, to the nearest tenths place.
Kimberly Reply
Jeannette has $5 and $10 bills in her wallet. The number of fives is three more than six times the number of tens. Let t represent the number of tens. Write an expression for the number of fives.
August Reply
What is the expressiin for seven less than four times the number of nickels
Leonardo Reply
How do i figure this problem out.
how do you translate this in Algebraic Expressions
linda Reply
why surface tension is zero at critical temperature
I think if critical temperature denote high temperature then a liquid stats boils that time the water stats to evaporate so some moles of h2o to up and due to high temp the bonding break they have low density so it can be a reason
Need to simplify the expresin. 3/7 (x+y)-1/7 (x-1)=
Crystal Reply
. After 3 months on a diet, Lisa had lost 12% of her original weight. She lost 21 pounds. What was Lisa's original weight?
Chris Reply
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Source:  OpenStax, Ece 320 - spring 2003. OpenStax CNX. Jan 22, 2004 Download for free at http://cnx.org/content/col10096/1.2
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