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more precise error-diffusion 

The Barbara test image has been looking right since commit 430dd67cb2.
However, t.pgm has not. This doesn't fix it, but does seem like an
improvement.

The remaining error seems to be unrelated to rounding. Adding 8 more
bits of precision has no effect.
This commit is contained in:
Kartik K. Agaram 2021-07-12 00:45:17 -07:00
parent 4e5e887e01
commit a4f36d60ef
2 changed files with 22221 additions and 33 deletions
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22190
barbara.pgm Normal file
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File diff suppressed because it is too large Load Diff

64
img.mu
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@ -27,19 +27,10 @@ fn main screen: (addr screen), keyboard: (addr keyboard), data-disk: (addr disk)
var img-storage: image
var img/esi: (addr image) <- address img-storage
load-image img, data-disk
render-image screen, img, 0/x, 0/y, 0x100/width, 0x100/height
#? render-image screen, img, 0x20/x, 0x180/y, 0x12c/width=300, 0xc8/height=200
#? render-pgm-image screen, img, 0x220/x, 0x180/y, 0x12c/width=300, 0xc8/height=200
#? render-image screen, img, 0x320/x, 0x280/y, 0x60/width=96, 0x1c/height=28
#? render-pgm-image screen, img, 0x1c0/x, 0x100/y, 0x12c/width=300, 0xc8/height=200
#? draw-box-on-real-screen 0x1bf/x, 0x102/y, 0x1c4/x, 0x104/y, 4/fg
#? render-image screen, img, 0x80/x, 0x100/y, 0x12c/width=300, 0xc8/height=200
#? set-cursor-position 0/screen, 0/x 2/y
#? render-pgm-image screen, img, 0x200/x, 0x100/y, 0x200/width, 0x200/height
#? render-image screen, img, 0/x, 0x100/y, 0x200/width, 0x200/height
#? render-image screen, img, 0/x, 0/y, 0x300/width, 0x300/height
render-image screen, img, 0x20/x, 0x80/y, 0x258/width=600, 0x190/height=400
#? render-image screen, img, 0x20/x, 0x80/y, 0x12c/width=300, 0xc8/height=200
#? render-pgm-image screen, img, 0x220/x, 0x80/y, 0x12c/width=300, 0xc8/height=200
}
fn load-image self: (addr image), data-disk: (addr disk) {
@ -501,34 +492,41 @@ fn dither-pgm-unordered _src: (addr image), _dest: (addr image) {
}
fn compute-greyscale-color-and-error errors: (addr array int), initial-color: byte, x: int, y: int, width: int -> _/eax: byte, _/esi: int {
# pseudocode:
# error += (initial-color << 16)
# nearest-color = nearest(error >> 16)
# error -= (nearest-color << 16)
# return nearest-color >> 4 + 16, error
var error/esi: int <- _read-dithering-error errors, x, y, width
# error += initial-color << 16
var color-int/eax: int <- copy initial-color
color-int <- shift-left 0x10 # we have 32 bits; we'll use 16 bits for the fraction and leave 8 for unanticipated overflow
error <- add color-int
# tmp = max(error, 0)
var tmp/eax: int <- copy error
# error += (initial-color << 16)
var tmp/eax: int <- copy initial-color
tmp <- shift-left 0x10 # we have 32 bits; we'll use 16 bits for the fraction and leave 8 for unanticipated overflow
error <- add tmp
# nearest-color = nearest(error >> 16)
var nearest-color/ecx: int <- copy error
nearest-color <- shift-right-signed 0x10
{
compare tmp, 0
compare nearest-color, 0
break-if->=
tmp <- copy 0
nearest-color <- copy 0
}
# round tmp to nearest multiple of 0x100000
# . round to nearest multiple of 0x10
{
var tmp2/ecx: int <- copy tmp
tmp2 <- and 0xfffff
compare tmp2, 0x80000
var tmp/eax: int <- copy nearest-color
tmp <- and 0xf
compare tmp, 8
break-if-<
tmp <- add 0x80000
nearest-color <- add 8
}
tmp <- and 0xf00000
# error -= tmp
nearest-color <- and 0xf0
# error -= (nearest-color << 16)
var tmp/eax: int <- copy nearest-color
tmp <- shift-left 0x10
error <- subtract tmp
# color = tmp >> 20 + 16
var color/eax: int <- copy tmp
color <- shift-right-signed 0x14
color <- add 0x10
var color-byte/eax: byte <- copy-byte color
# return (nearest-color >> 4 + 16), error
nearest-color <- shift-right 4
nearest-color <- add 0x10
var color-byte/eax: byte <- copy-byte nearest-color
return color-byte, error
}