Editing Text Images (section)

== bitmap images ==
You probably have heard before that bitmap images are grids of pixels, where
* resolution: the number of horizontal and vertical pixels. E.g. 1920x1080 is 1920 pixels wide and 1080 high
* color depth: the number of bits used to indicate the color of a single pixel

for a good introduction to bit maps see: See Bourke, Paul. n.d. ‘A Beginners Guide to Bitmaps’. Accessed 2 January 2018. http://paulbourke.net/dataformats/bitmaps/.


===Resolutions: ===

Color depth - (use microscope) 
* [[Binary image|1-bit color]] (2<sup>1</sup> = 2 colors): '''monochrome''', often black and white, compact [[Macintosh]]es, [[Atari ST]].
* 2-bit color (2<sup>2</sup> = 4 colors): [[Color Graphics Adapter|CGA]], gray-scale early [[NeXTstation]], color Macintoshes, Atari ST.
* 3-bit color (2<sup>3</sup> = 8 colors): many early home computers with TV displays, including the [[ZX Spectrum]] and [[BBC Micro]]
* 4-bit color (2<sup>4</sup> = 16 colors): as used by [[Enhanced Graphics Adapter|EGA]] and by the least common denominator VGA standard at higher resolution, color Macintoshes, Atari ST, [[Commodore 64]], [[Amstrad CPC]].
* 5-bit color (2<sup>5</sup> = 32 colors): [[Original Amiga chipset]]
* 6-bit color (2<sup>6</sup> = 64 colors): Original Amiga chipset
* [[8-bit color]] (2<sup>8</sup> = 256 colors): most early color Unix workstations, [[VGA]] at low resolution, [[Super VGA]], color Macintoshes, [[Atari TT]], [[Advanced Graphics Architecture|Amiga AGA chipset]], [[Falcon030]], [[Acorn Archimedes]].
* 12-bit color (2<sup>12</sup> = 4096 colors): some [[Silicon Graphics]] systems, Color NeXTstation systems, and [[Amiga]] systems in [[Hold And Modify|HAM]] mode.
* '''8-bit color''': A very limited but true direct color system, there are 3 bits (8 possible levels) for each of the R and G components, and the two remaining bits in the byte pixel to the B component (four levels), enabling 256 (8 × 8 × 4) different colors.
* Grey scale (8-bit)
* True color (24-bit): Usually, true color is defined to mean 256 shades of red, green, and blue, for a total of 224, or alternately 2563, or 16,777,216 color variations. The human eye can discriminate up to ten million colors
<ref>https://en.wikipedia.org/wiki/Color_depth</ref>


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===converting resolution===
with Imagemagick

to 100px wide
 convert myimage.jpg -resize 100x output.jpg 

to 100px  hight
 convert myimage.jpg -resize x100 output.jpg 

to 100x100px (image will loose its proportion; hence the "!" so imagemagick is sure that you wanna do that:)
 convert myimage.jpg -resize 100x100! output.jpg 

===converting color (bit depth)===

convert an image into monochrome (1 bit depth) image: 2color values (b/w)
 convert myimage.jpg -colorspace gray -depth 1 out.png

(2 bit depth) image: 4 color values
 convert myimage.jpg -colorspace gray -depth 2 out.png

(3 bit depth) image: 8 color values
 convert myimage.jpg -colorspace gray -depth 3 out.png

(4 bit depth) image: 16 color values
 convert myimage.jpg -colorspace gray -depth 4 out.png

(8 bit depth) image: 256 color values
 convert myimage.jpg -colorspace gray -depth 4 out.png


How can we be certain about this? How do can we see the grid that forms a bitmap image?
* magnify any digital screen 
* a Plain-text bitmap: where you can read each pixel: X PixMap (XPM)
  
[https://en.wikipedia.org/wiki/X_PixMap X PixMap (XPM)] is a plain-text bitmap image format, where each color is assigned a character, which is mapped onto the text space.

 convert myimage.jpg out.xpm


<source lang="c">
/* XPM */
static char *output[] = {
/* columns rows colors chars-per-pixel */
"50 73 2 1 ",
"  c black",
". c white",
/* pixels */
"                                                  ",
"                                                  ",
"                                                  ",
"                                                  ",
"               ................                   ",
"           ......   . .. . . .......              ",
"          .. .           .         ...            ",
"         . .   .. .            .     ..           ",
"        .. . .    .    .  .     .     .           ",
"        .   .      .    .   .    . .  ..          ",
"        .  .        .  .       .    . .           ",
"        ...          ..      .       ..           ",
"       ...              .. .         ...          ",
"        ..                            .           ",
"        .                             ..          ",
"        ..                            .           ",
"        .                             ..          ",
"       ...      .                     .           ",
"        .     .                       .           ",
"       ..                             .           ",
"       ..  .    .                   . .           ",
"        .    .                        .           ",
"       ..  .  .....                   .           ",
"        .    ..   ..                  .           ",
"        .   .       ..            .   .           ",
"       .  ..         .               ..           ",
"       .. .    .     .            .....           ",
"          .   ...     .          .    .           ",
"       .  .   ....   ..          .    ..          ",
"       . ..   ....              .      .          ",
"        . .          .          .    ....         ",
"       .  .          .          ..   ...          ",
"          .          .           .    ..          ",
"       ..  .        .            .     .          ",
"       .   .       ..            .    .           ",
"       .    ..   ..               ..  ..          ",
"       ..     ...                  ... .          ",
"      ..                               ..         ",
"      .                  .  .       .   .         ",
"     .  .  ..                           .         ",
"     .  . ....                     .    .         ",
"     .    ..  ...   .              ..  ..         ",
"     .. .  ..  .....   . ..   .   ...  .          ",
"      .    ... ..  ....          ....  .          ",
"       .    .....   ......     ...... .           ",
"       ..    . ..... .  ......... ... .           ",
"        ..   .........   .. .  ...... .           ",
"         .    ..   ....................           ",
"         .     ..   . ............... .           ",
"          .     .. ..   ............. .           ",
"           .      ..    .   .  .....  .           ",
"           ...  .  ...  .  .. ......  .           ",
"            ... .    .............    .           ",
"              ..   .       ..          .          ",
"               ...   ..                           ",
"                 ...     .    .       ..          ",
"                   ..            .    .           ",
"                     ..               .           ",
"                       ....          ..           ",
"                          .....  ....             ",
"                              .....               ",
"                                                  ",
"                                     .            ",
"                   ..   .            ...          ",
"        ...  .. ..  ... .. .. ...... ...          ",
"        ............................  ..          ",
"        ...... ................. ...  .           ",
"        ......  ... ... ..... .... .. .           ",
"        ..                                        ",
"        .                                         ",
"                                                  ",
"                                                  ",
"                                                  "
};

</source>




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