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Image Data and Display

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  1. Image Data and Display

  2. For Class Consistency % source ~rvrpci/.simg726.rc

  3. Quiz #2 Topics • mkdir • chmod • cd • grep • ci and co

  4. PBMPLUS FORMAT and xv • Digital image format concepts • PBMPLUS image interchange format. • Displaying digital image • xv image display

  5. PBMPLUS Image Data Types • Bilevel Image Data Type • Black and White • Monochrome Image Data Type • Greyscale • RGB Color Image Data Type • Color

  6. Two PBMPLUS Representations • All PBMPLUS data formats have the following representations • ASCII Format • (for Human Consumption) • RAW Format • (for Computer Consumption)

  7. Displaying Images • Use xv utility for display and documentation purposes. • Note that xv is an X client • Should NEVER be used for image processing • USE ONLY FOR DISPLAY PURPOSES • To invoke xv % xv & % xv filename.pgm &

  8. Portable Bit Map (PBM) • Bilevel Image Data Type • (Black and White) • Used to represent printed black and white imagery such as documents and faxes. • Uses 0’s (zeroes) to represent white • (no ink deposited on paper) • Uses 1’s (ones) to represent black • (ink deposited on paper)

  9. Let us digress – The vi Problem • vi practice and creation of a bilevel image. • 7”x10” graph paper divided into 10 squares per inch. • Cell not covered by ink • value of zero (0). • Cell fully or partially covered by ink • value of one (1). • You will have a total of 700 pixels to enter.

  10. Problem #1 Solution • vi - Brute Force Solution 1. Is the current pixel 0 (zero) or 1 (one)? 2. Type the appropriate character 3. Repeat steps 1 and 2 until done

  11. Problem #1 Solution • vi- Smart Solution 1. Type the vi command “70i0” “seventy, i - for insert, 0 (zero)” 2. Hit the ESCAPE key to get you out of insert mode. 3. Type the vi command “o” to open a new line 4. Hit the ESCAPE key to get you out of insert mode. 5. Move back up to the line of zeroes and use the yy (yank command) to make a copy of the line of 70 zeroes.

  12. Problem #1 Solution • vi- Smart Solution 6. Type the vi command “p”10 times 7. Move back up to the top line of zeroes and use the 10yy (yank command) to make a copy of 10 lines of 70 zeroes per line. 8. Type the vi command “p”10 times 9.You will now have a page of 700 zeroes.

  13. Problem #1 Solution • vi- Smart Solution 10. You can navigate to the areas that need to be changed to “1” and use the “R” command to replace contiguous set of characters. 11. Hit the ESCAPE key to get you out of insert mode. 12. Navigate to next section and repeat steps 10 -12 until done. 13. Save the file out and exit vi :wq signature.dat

  14. Yet another vi Digression • To show line number in vi, execute the following command :set number • To disable line numbers in vi, execute the following command :set nonumber

  15. Viewing current vi settings :set all noautoindent nomodelines noshowmode autoprint nonumber noslowopen noautowrite nonovice tabstop=8 nobeautify nooptimize taglength=0 directory=/var/tmp paragraphs=IPLPPPQPP LIpplpipnpbtags=tags /usr/lib/tags noedcompatible prompt tagstack noerrorbells noreadonly term=vt220 noexrc redraw noterse flash remap timeout hardtabs=8 report=5 ttytype=vt220 noignorecase scroll=11 warn nolisp sections=NHSHH HUuhsh+c window=23 nolist shell=/bin/csh wrapscan magic shiftwidth=8 wrapmargin=0 mesg noshowmatch nowriteany

  16. Saving vi Preferences • Preferences such as :set number can be saved in the file .exrc in your home directory (~)

  17. A vi Command to Always Remember • To replace all occurrences or a string in a file with new string. :%s/string1/string2/g OR :%s/string1/string2/gc (Will ask you for confirmation)

  18. The Super-smart Solution • In UNIX % repeat 70 echo -n 0 >> one_line; echo >> one_line; repeat 100 cat one_line >> signature.dat

  19. Let’s Create another image • Put the signature.dat away for the time being and create a simpler image • Call it bilevel.pbm

  20. Portable Bit Map (PBM) • Bilevel Image Data Type • For the ASCII file format, the file header is given by P1 • width and height of the image. • Comments are indicated by the # character P1 # This is a 16 column x 3 row # PBM ASCII image # Created by using vi 16 3 001010100011010000111110 010010000101001001011100

  21. Portable Bit Map (PBM) • Make a copy of bilevel.pbm and edit the copy to look like the following, P1 #This is a 16 column x 3 row PBM ASCII #image # 16 3 0010101000110100 0011111001001000 0101001001011100

  22. Portable Bit Map (PBM) • When displayed looks like P1 # This is a 16 column x 3 row PBM ASCII # image # 16 3 0010101000110100 0011111001001000 0101001001011100

  23. How to Add a PBMPLUS Header to an Image File • If its an ASCII file you can use vi • Use the cat command to concatenate a header from a file or the keyboard (standard input - stdio)

  24. Put a header on signature.dat and display in xv • Method #1 • Using a text editor, input the appropriate header values.

  25. Put a header on signature.dat and display in xv • Method #2 • Edit a file calledheader.dat containing the header information • Concatenate the header file at the beginning of signature.dat using the cat command % cat header.dat signature.dat > signature.pbm

  26. Put a header on signature.dat and display in xv • Method #3 • Concatenate the header data from the keyboard directly to the beginning of signature.dat using the cat command % cat - signature.dat > signature.pbm P1 70 100 ^D

  27. Portable Bit Map (PBM) • There is also a binary version of the PBM image type which uses a P4 header such as the one below P4 # This is a 16 column x 3 row PBM RAW # image 16 3 *4>HR\

  28. Portable Grey Map (PGM) • Monochrome Image Data Type (Greyscale) • Displayed greyscale imagery • Grey values µ brightness. • Convention opposite that of the PBM format

  29. Portable Grey Map (PGM) • Monochrome Image Data Type (Greyscale) • EXAMPLE, P2 # This is a 3 column x 2 row PGM ASCII image # With a possible maximum grey value of 255 3 2 255 42 52 62 72 82 92

  30. Portable Grey Map (PGM) • When displayed, the image is shown below P2 # This is a 3 column x 2 row PGM ASCII image # With a possible maximum grey value of 255 3 2 255 42 52 62 72 82 92

  31. Portable Grey Map (PGM) • There is also a binary version of the PGM image type which uses a P5 header such as the one below P5 # This is a 3 column x 2 row PGM Raw # image 3 2 255 *4>HR\

  32. Portable Pixel Map (PPM) • RGB Color Image Data Type (Color) • Red, Green, and Blue bands • Arranged in pixel-interleaved format or band interleaved by pixel (BIP)

  33. Portable Pixel Map (PPM) • RGB Color Image Data Type (Color) • For the ASCII file format, • P3 • width, height • maximumgrey levelpossible of the image • The pixel values are given as a triple representing the red, green, and blue components .

  34. Portable Pixel Map (PPM) • RGB Color Image Data Type (Color) • EXAMPLE, P3 3 3 255 255 0 0 0 255 0 0 0 255 128 0 0 0 128 0 0 0 128 0 0 0 128 128 128 255 255 255

  35. PPM QUESTION So what does the data*4>HR\look like as a Raw PPM Image?

  36. Conversion of Raw Files to PBMPLUS Format • Alternative to manually prepending a header file using cat command rawtopbm, rawtopgm, or rawtoppm % rawtopgm 256 256 ~rvrpci/pub/MyCat_P5.raw > MyCat.pgm

  37. Usage Note About PBMPLUS Commands • PBMPLUS commands heavily use the UNIX redirection and piping • To get help use -h option. % rawtopgm -h usage: rawtopgm [-headerskip N] [-rowskip N] [-tb|-topbottom] [<width> <height>][rawfile]

  38. Converting PNM Image File to Another Format • PNM is a generic designator for all PBM, PGM, and PPM • Convert a PBMPLUS format file into a TIFF • e.g., signature.pbm to signature.tiff. • Use the following command % pnmtotiff -none signature.pbm > signature.tiff -noneoption means not invoke LZW image compression.

  39. TIFF FILE PNM FILE 2X Scale PNM FILE RAST FILE Rudimentary Image Processing Using the PBMPLUS Utilities • Requires that all input be in some form of PBM, PGM, PPM image • Supposed we wanted to enlarge a tiff file ( e.g., signature.tiff) by a scale factor of 2x and then convert it to a SUN raster file.

  40. Rudimentary Image Processing Using the PBMPLUS Utilities • The previous process can actually be executed in one UNIX command % tifftopnm signature.tiff | pnmscale 2.0 | pnmtorast > signature.rast • In fact you can pipe the information directly to xv before writing it out to another format % tifftopnm signature.tiff | pnmscale 2.0 | pnmtorast | xv -

  41. PBMPLUS File Information • Supposed you wanted to know what the characteristics are of a particular PBMPLUS file you can give the following command % pnmfile MyCat.pgm MyCat.pgm: PGM raw, 256 by 256 maxval 255

  42. PBMPLUS Histogram Utilities • Greyscale histogram pgmhist • Color histogram ppmhist

  43. Cutting out regions of interest % pnmcut usage: pnmcut x y width height [pnmfile] % pnmcrop usage: pnmcrop [-white|-black] [-left] [-right] [-top] [-bottom] [pnmfile]

  44. Pasting or Arranging Images % pnmcat pnmcat [-white|-black] -leftright|-lr [-jtop|-jbottom] pnmfile pnmfile ... % pnmpaste pnmpaste [-replace|-or|-and |xor] frompnmfile x y [intopnmfile]

  45. You have a bunch of images... % pnmindex pnmindex [-size N] [-across N] [-colors N] [-black] pnmfile ...

  46. Color Bands Combination and Extraction % rgb3ppm rgb3toppm redpgmfile greenpgmfile bluepgmfile % ppmtorgb3 ppmtorgb3 [ppmfile] • results in .red .grn .blu

  47. Spatial Operations • pnmconvol • pnmscale • pnmrotate • pnmflip • pnmshear

  48. Greyscale/Color Operations • ppmquant • pnmdepth • ppmdither

  49. Really Useful Stuff • Doing Screen Captures under X % xwd | xwdtopnm | pnmdepth 255 | pnmtotiff > screen.tif • Your cursor will turn into crosshairs • Click on the window you want to capture

  50. Screen Capture through xv • Click on grab button • Specify a time delay • Left button grabs window • Middle button grabs a rectangle • Right button cancels