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Rolando V. Raqueño Tuesday, April 18, 202311
Quiz #6 Topics
• cut• paste• sort• tail• head
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Rolando V. Raqueño Tuesday, April 18, 202322
Numbering SystemsDECIMAL BINARY OCTAL HEXADECIMAL(Base 10) (Base 2) (Base 8) (Base 16)
0 0 0 01 1 1 12 10 2 23 11 3 34 100 4 45 101 5 56 110 6 67 111 7 78 1000 10 89 1001 11 910 1010 12 A11 1011 13 B12 1100 14 C13 1101 15 D14 1110 16 E15 1111 17 F
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Rolando V. Raqueño Tuesday, April 18, 202333
Converting Between Bases
• 42 base 10 converted to base 10,
• 42 base 10 converted to base 8,
4210 4 101 40 2 100 2 4210
4210 5 81 40 2 80 2 528
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Rolando V. Raqueño Tuesday, April 18, 202344
Converting Between Bases
• 42 base 10 converted to base 2,
• 42 base 10 converted to base 16,
4210 125 32 0 24 0 123 8 0 22 0 121 2 0 20 0 1010102
4210 2 161 32 a 160 10 2a16
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Rolando V. Raqueño Tuesday, April 18, 202355
Number Base Conversion using bc
• To convert decimal to binaryobase=242101010
• To convert octal to hexadecimalobase=16ibase=8522A
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Rolando V. Raqueño Tuesday, April 18, 202366
Negative Number Representation
DECIMAL DECIMAL BINARY(Base 10) (4-digit) (4-digit)
-8 9992 1000-7 9993 1001-6 9994 1010-5 9995 1011-4 9996 1100-3 9997 1101-2 9998 1110-1 9999 11110 0 00001 1 00012 2 00103 3 00114 4 01005 5 01016 6 01107 7 0111
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Rolando V. Raqueño Tuesday, April 18, 202377
Converting a Negative Number into Binary using 2’s Complement
• To convert -42 into a negative binary value – Determine the number of bits to represent (e.g.
16 bits)– Convert the absolute value (42) into binary
0000000000101010
– Take the 1’s complement of the number1111111111010101
– Add 1 to the number1111111111010110
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Rolando V. Raqueño Tuesday, April 18, 202388
Floating Point Representation
• Sets of bits are separated into – mantissa
– exponent field
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Rolando V. Raqueño Tuesday, April 18, 202399
Another Example of Unformatted Output (e.pro)
pro e
openw, lun, 'e.dat', /get_lun e = exp(1.0) writeu,lun, e free_lun, lun
end
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Rolando V. Raqueño Tuesday, April 18, 20231010
Octal Interpretation of e.dat (big endian)
% od -b e.dat0000000 100 055 370 1240000004
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Rolando V. Raqueño Tuesday, April 18, 20231111
Binary Interpretation of e.dat (big endian)
% bc -lobase=2ibase=8100100000055101101370111110001241010100
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Rolando V. Raqueño Tuesday, April 18, 20231212
Binary Interpretation of e.dat (big endian)
01000000 00101101 11111000 01010100
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Rolando V. Raqueño Tuesday, April 18, 20231313
(SINGLE PRECISION) - IEEE (ANSI/IEEE Std 754-
1985)
+-+--------+-----------------------+ |S| exp | fraction | +-+--------+-----------------------+ ^ ^ Bit31 Bit0
A formula that gives the value of this float is:
Value=(-1)**S X 1.fraction X 2**(exp-127)
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Rolando V. Raqueño Tuesday, April 18, 20231414
Binary Interpretation of e.dat (big endian)
01000000 00101101 11111000 01010100
[Bit 31]S = 0[Bits 30:23] exp = 1000000 0 = 128 (decimal)[Bits 22:0]fraction = 0101101 11111000 01010100
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Rolando V. Raqueño Tuesday, April 18, 20231515
(SINGLE PRECISION) - IEEE (ANSI/IEEE Std 754-
1985)Value=(-1)**S X 1.fraction X 2**(exp-127)
2**(128-127)= 2
% bc -libase=21.0101101 11111000 010101001.35914087295532226562500ibase=10102*1.359140872955322265625002.71828174591064453125000
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Rolando V. Raqueño Tuesday, April 18, 20231616
Floating Point Interpretation of e.dat (big endian)
% od -f e.dat0000000 2.7182817e+000000004
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Rolando V. Raqueño Tuesday, April 18, 20231717
Debugging in IDL
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Rolando V. Raqueño Tuesday, April 18, 20231818
Basic IDL Debugging Commands
breakpoint
.step (.s)
.stepover (.so)
.continue
.return
.out
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Rolando V. Raqueño Tuesday, April 18, 20231919
mean.pro
10 ;- 11 ;
12 function mean,x
13 n = n_elements(x)
14 answer = sum(x)/double(n)
15 return, answer
16 end
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Rolando V. Raqueño Tuesday, April 18, 20232020
Breakpoints
IDL> breakpoint, ‘mean.pro’, 12
IDL> help,/breakpoint
Breakpoints:
Index Module Line File
----- ------ ---- ----
0 MEAN 12 mean.pro
IDL> breakpoint, /clear, 0
OR
IDL> breakpoint, /clear, ‘mean.pro’, 12
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Rolando V. Raqueño Tuesday, April 18, 20232121
.step
• Used after a breakpoint is reached
• Single step through commands
• If statement is a function or procedure– Will enter into it
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Rolando V. Raqueño Tuesday, April 18, 20232222
.stepover
• Similar to .step • Executes functions and procedures to
completion without stopping inside the function
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Rolando V. Raqueño Tuesday, April 18, 20232323
.return
• Continues execution until a return statement is encountered.
• Useful in checking the return value of an inner (nested) function in a function composition
• e.g.
sqrt(variance(x))
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Rolando V. Raqueño Tuesday, April 18, 20232424
.out
• Continues execution out of the current routine.
• Useful in leaving a routine that you stepped into, but have determined that all is working properly and want to return to the calling routine.
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Rolando V. Raqueño Tuesday, April 18, 20232525
mean.pro
10 ;- 11 ; 12 function mean,x 13 n = n_elements(x) 14 answer = sum(x)/double(n) 15 return, answer 16 end
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Rolando V. Raqueño Tuesday, April 18, 20232626
Mystery Images
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Rolando V. Raqueño Tuesday, April 18, 20232727
Given an image of unknown origin
• Dimensions of the image?– Most importantly the number of samples
• Aspect ratio of the image? • Number of bytes per pixel?• Number of bands of the image?• Number of bits per pixel?• External or internal compression applied
– gzip– tiff or jpeg
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Rolando V. Raqueño Tuesday, April 18, 20232828
Know the imaging instrument
• Find out what kind of image capture device– Framing Camera with filters
• Band Sequential Images (BSQ)
– Flatbed of Pushbroom scanner• Band interleaved by line (BIL)
– Line Scanner• Band interleaved by pixel (BIP)
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Rolando V. Raqueño Tuesday, April 18, 20232929
Tools at your disposal for dissecting the image
% file% anytopnm % more% ls -l% bc -l% od% dd% strings% rawtopgm or cat% xv
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Rolando V. Raqueño Tuesday, April 18, 20233030
file
• Uses information in /etc/magic to determine the type of a file.
• Common outputs from the file command% file irod.img.gz
irod.img.gz: gzip compressed data - deflate method , original file name , max compression
% file readme
readme: ascii text
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Rolando V. Raqueño Tuesday, April 18, 20233131
File (more examples)
% file RIT_bip.imgRIT_bip.img: data
% file modtran4.batmodtran4.bat: executable c-shell script
bean% file maincode.exemaincode.exe: ELF 32-bit MSB executable SPARC Version 1, dynamically linked, not stripped
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Rolando V. Raqueño Tuesday, April 18, 20233232
File (image examples)Don’t always believe the extensions
bean% file feep.tif
feep.tif: TIFF file, big-endian
bean% file feep.pgm
feep.pgm: PGM ascii file
bean% file AVIRIS_RIT.jpg
AVIRIS_RIT.jpg: JPEG file
bean% file rotate.pbm
rotate.pbm: PGM raw file
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Rolando V. Raqueño Tuesday, April 18, 20233333
anytopnm
• Shell script that does a brute force test on images and converts to pnm format
% anytopnm mystery_file > mystery_file.pnm
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Rolando V. Raqueño Tuesday, April 18, 20233434
od
• Can be used to quickly check the minimum and maximum values in a file
• Stupid UNIX Trick% od –d –v image.raw | cut –c10- | tr –s “ “ “\012” | sort –nu | head
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Rolando V. Raqueño Tuesday, April 18, 20233535
Xv and NetPBM
• Xv want multi-byte NetPBM files in little-endian form
• N.B. NetPBM utilities behave inconsistently for multi-byte data
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Rolando V. Raqueño Tuesday, April 18, 20233636
Can you guess the dimensions of the image?
• Try to guess the number of rows (width) first.– Possible guesses
•256•512•2^n•2^n+2^(n-1)
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Rolando V. Raqueño Tuesday, April 18, 20233737
Can you guess the aspect ratio of the image?
• wc -c or ls -l – determine how many bytes are in the image
• Square root of the image size – Multiple of a perfect square
• Assume that the image is greyscale & square– use rawtopgm
% rawtopgm 512 512 image.raw > image.pgm
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Rolando V. Raqueño Tuesday, April 18, 20233838
Square Gray Scale Image
• Used rawtopgm to create a pgm file and then use xv to display
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Rolando V. Raqueño Tuesday, April 18, 20233939
A convenient little trick
• If you are just experimenting with a mystery image
% rawtopgm 512 512 image.raw | xv -
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Rolando V. Raqueño Tuesday, April 18, 20234040
Does it have a header?
• Not a perfect square– go ahead and try to display it as if it were a
square image to see if it has a header.
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Rolando V. Raqueño Tuesday, April 18, 20234141
Square Grey Scale image with a header
• This structure means you have a header in the file that is causing a uniform shift
• You can fix this by using dd
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Rolando V. Raqueño Tuesday, April 18, 20234242
Square image no header
• Your guess on the width of the image is short by one pixel
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Rolando V. Raqueño Tuesday, April 18, 20234343
Square image no header
• Your guess on the width of the image is long by one pixel
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Rolando V. Raqueño Tuesday, April 18, 20234444
Square image no header
• You probably guessed a little too low on the width of this image
• (off by 6 pixels)
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Rolando V. Raqueño Tuesday, April 18, 20234545
Square Image with no header
• Your probably guessed a little too high on the width of the image
• (off by 6 pixels)
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Rolando V. Raqueño Tuesday, April 18, 20234646
A color image displayed as greyscale image
• Correct dimensions– 256x256x3 BIP
• Incorrectly assumed– 443x443 image with
header
• N.B. 196608/3=256^2
• Indicates a multiband image
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Rolando V. Raqueño Tuesday, April 18, 20234747
Multiband Assumption
• Once multiband image is assumed– Need to determine interleaving– Can be deduced by displaying first band– This assumes you have a guess of image
dimension
• Extract the first band out using dd
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Rolando V. Raqueño Tuesday, April 18, 20234848
First band of color image file assumed to be BSQ
• Assume a square image for first band
• Color image file obviously not BSQ
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Rolando V. Raqueño Tuesday, April 18, 20234949
Square color image displayed as a greyscale (3:1 aspect ratio)
• Original image 3x256x256
• Displayed it as a greyscale 768x256
• To get insight into interleaving structure.
• BIP file would look like the left image
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Rolando V. Raqueño Tuesday, April 18, 20235050
Square color image displayed as greyscale( 3:1 aspect ratio)
• This is how a BIL image would behave• What we have here is the individual bands
side by side
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Rolando V. Raqueño Tuesday, April 18, 20235151
• This is how a BSQ file would behave
Square color image displayed as greyscale( 3:1 aspect ratio)
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Rolando V. Raqueño Tuesday, April 18, 20235252
Multibyte pixel image
• Need to be careful about the endian of the machine on which the image was written
• Can use dd to swap bytes for short integer images (2-bytes per pixel) or the swap_endian function in IDL
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Rolando V. Raqueño Tuesday, April 18, 20235353
Mystery Image Examples
• Check Webpage for sources of examples.
• An example will be given for the midterm exam.