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ii-pix
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Add comments and tidy up some more

This commit is contained in:
kris 2021-03-15 17:22:14 +00:00
parent 101d974d50
commit 527f6504f7
2 changed files with 107 additions and 24 deletions
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118
dither.pyx
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@ -9,7 +9,9 @@ from libc.stdlib cimport malloc, free
# TODO: use a cdef class
# C representation of dither_pattern.DitherPattern data, for efficient access.
cdef struct Dither:
float* pattern # Flattened dither pattern
int x_shape
int y_shape
@ -21,24 +23,29 @@ cdef float clip(float a, float min_value, float max_value) nogil:
return min(max(a, min_value), max_value)
# Compute left-hand bounding box for dithering at horizontal position x.
cdef int dither_bounds_xl(Dither *dither, int x) nogil:
cdef int el = max(dither.x_origin - x, 0)
cdef int xl = x - dither.x_origin + el
return xl
#Compute right-hand bounding box for dithering at horizontal position x.
cdef int dither_bounds_xr(Dither *dither, int x_res, int x) nogil:
cdef int er = min(dither.x_shape, x_res - x)
cdef int xr = x - dither.x_origin + er
return xr
# Compute upper bounding box for dithering at vertical position y.
cdef int dither_bounds_yt(Dither *dither, int y) nogil:
cdef int et = max(dither.y_origin - y, 0)
cdef int yt = y - dither.y_origin + et
return yt
# Compute lower bounding box for dithering at vertical position y.
cdef int dither_bounds_yb(Dither *dither, int y_res, int y) nogil:
cdef int eb = min(dither.y_shape, y_res - y)
cdef int yb = y - dither.y_origin + eb
@ -49,11 +56,22 @@ cdef int dither_bounds_yb(Dither *dither, int y_res, int y) nogil:
@cython.wraparound(False)
@functools.lru_cache(None)
def lookahead_options(object screen, int lookahead, unsigned char last_pixel_nbit, int x):
"""Compute all possible n-bit palette values for upcoming pixels, given x coord and state of n pixels to the left.
Args:
screen: python screen.Screen object
lookahead: how many pixels to lookahead
last_pixel_nbit: n-bit value representing n pixels to left of current position, which determine available
colours.
x: current x position
Returns: matrix of size (2**lookahead, lookahead) containing all 2**lookahead possible vectors of n-bit palette
values accessible at positions x .. x + lookahead
"""
cdef unsigned char[:, ::1] options_nbit = np.empty((2 ** lookahead, lookahead), dtype=np.uint8)
cdef int i, j, xx, p
cdef unsigned char output_pixel_nbit
cdef unsigned char[::1] palette_choices_nbit
cdef unsigned char[:, ::1] palette_choices_rgb
cdef object palette = screen.palette
cdef dict palette_rgb = palette.RGB
@ -61,27 +79,36 @@ def lookahead_options(object screen, int lookahead, unsigned char last_pixel_nbi
output_pixel_nbit = last_pixel_nbit
for j in range(lookahead):
xx = x + j
# Two possible n-bit palette choices at position xx, given state of n pixels to left.
# TODO: port screen.py to pyx
palette_choices_nbit, _ = screen.pixel_palette_options(output_pixel_nbit, xx)
palette_choices_nbit = screen.pixel_palette_options(output_pixel_nbit, xx)
output_pixel_nbit = palette_choices_nbit[(i & (1 << j)) >> j]
options_nbit[i, j] = output_pixel_nbit
return options_nbit
# Look ahead a number of pixels and compute choice for next pixel with lowest total squared error after dithering.
#
# Args:
# dither: error diffusion pattern to apply
# palette_rgb: matrix of all n-bit colour palette RGB values
# image_rgb: RGB image in the process of dithering
# x: current horizontal screen position
# y: current vertical screen position
# options_nbit: matrix of (2**lookahead, lookahead) possible n-bit colour choices at positions x .. x + lookahead
# lookahead: how many horizontal pixels to look ahead
# distances: matrix of (24-bit RGB, n-bit palette) perceptual colour distances
# x_res: horizontal screen resolution
#
# Returns: index from 0 .. 2**lookahead into options_nbit representing best available choice for position (x,y)
#
@cython.boundscheck(False)
@cython.wraparound(False)
cdef int dither_lookahead(Dither* dither, float[:, ::1] palette_rgb,
float[:, :, ::1] image_rgb, int x, int y, unsigned char[:, ::1] options_nbit, int lookahead,
unsigned char[:, ::1] distances, int x_res):
cdef int i, j, k, l
# Don't bother dithering past the lookahead horizon or edge of screen.
cdef int xxr = min(x + lookahead, x_res)
cdef int lah_shape1 = xxr - x
cdef int lah_shape2 = 3
cdef float *lah_image_rgb = <float *> malloc(lah_shape1 * lah_shape2 * sizeof(float))
cdef float[3] quant_error
cdef unsigned char bit4
cdef int best
@ -90,6 +117,17 @@ cdef int dither_lookahead(Dither* dither, float[:, ::1] palette_rgb,
cdef long flat, dist
cdef long r, g, b
# Don't bother dithering past the lookahead horizon or edge of screen.
cdef int xxr = min(x + lookahead, x_res)
cdef int lah_shape1 = xxr - x
cdef int lah_shape2 = 3
cdef float *lah_image_rgb = <float *> malloc(lah_shape1 * lah_shape2 * sizeof(float))
# For each 2**lookahead possibilities for the on/off state of the next lookahead pixels, apply error diffusion
# and compute the total squared error to the source image. Since we only have two possible colours for each
# given pixel (dependent on the state already chosen for pixels to the left), we need to look beyond local minima.
# i.e. it might be better to make a sub-optimal choice for this pixel if it allows access to much better pixel
# colours at later positions.
for i in range(1 << lookahead):
# Working copy of input pixels
for j in range(xxr - x):
@ -127,8 +165,20 @@ cdef int dither_lookahead(Dither* dither, float[:, ::1] palette_rgb,
return best
# Perform error diffusion to a single image row.
#
# Args:
# dither: dither pattern to apply
# xl: lower x bounding box
# xr: upper x bounding box
# x: starting horizontal position to apply error diffusion
# image: array of shape (image_shape1, 3) representing RGB pixel data for a single image line, to be mutated.
# image_shape1: horizontal dimension of image
# quant_error: RGB quantization error to be diffused
#
cdef void apply_one_line(Dither* dither, int xl, int xr, int x, float[] image, int image_shape1,
float[] quant_error) nogil:
cdef int i, j
cdef float error_fraction
@ -138,9 +188,21 @@ cdef void apply_one_line(Dither* dither, int xl, int xr, int x, float[] image, i
image[i * image_shape1 + j] = clip(image[i * image_shape1 + j] + error_fraction * quant_error[j], 0, 255)
# Perform error diffusion across multiple image rows.
#
# Args:
# dither: dither pattern to apply
# x_res: horizontal image resolution
# y_res: vertical image resolution
# x: starting horizontal position to apply error diffusion
# y: starting vertical position to apply error diffusion
# image: RGB pixel data, to be mutated
# quant_error: RGB quantization error to be diffused
#
@cython.boundscheck(False)
@cython.wraparound(False)
cdef void apply(Dither* dither, int x_res, int y_res, int x, int y, float[:,:,::1] image, float[] quant_error):
cdef int i, j, k
cdef int yt = dither_bounds_yt(dither, y)
@ -160,10 +222,21 @@ cdef void apply(Dither* dither, int x_res, int y_res, int x, int y, float[:,:,::
image[i,j,k] = clip(image[i,j,k] + error_fraction * quant_error[k], 0, 255)
# Compute closest colour from array of candidate n-bit colour palette values.
#
# Args:
# pixel_rgb: source RGB colour value to be matched
# options_nbit: array of candidate n-bit colour palette values
# distances: matrix of (24-bit RGB value, n-bit colour value) perceptual colour differences
#
# Returns:
# index of options_nbit entry having lowest distance value
#
@cython.boundscheck(False)
@cython.wraparound(False)
cdef unsigned char find_nearest_colour(float[::1] pixel_rgb, unsigned char[::1] options_nbit,
unsigned char[:, ::1] options_rgb, unsigned char[:, ::1] distances):
unsigned char[:, ::1] distances):
cdef int best, dist
cdef unsigned char bit4
cdef int best_dist = 2**8
@ -180,6 +253,17 @@ cdef unsigned char find_nearest_colour(float[::1] pixel_rgb, unsigned char[::1]
return options_nbit[best]
# Dither a source image
#
# Args:
# screen: screen.Screen object
# image_rgb: input RGB image
# dither: dither_pattern.DitherPattern to apply during dithering
# lookahead: how many x positions to look ahead to optimize colour choices
# verbose: whether to output progress during image conversion
#
# Returns: tuple of n-bit output image array and RGB output image array
#
@cython.boundscheck(False)
@cython.wraparound(False)
def dither_image(screen, float[:, :, ::1] image_rgb, dither, int lookahead, unsigned char verbose):
@ -190,7 +274,6 @@ def dither_image(screen, float[:, :, ::1] image_rgb, dither, int lookahead, unsi
cdef float[:, :, ::1] options_rgb
cdef unsigned char [:, ::1] lookahead_palette_choices_nbit
cdef unsigned char [::1] palette_choices_nbit
cdef unsigned char [:, ::1] palette_choices_rgb
cdef unsigned char output_pixel_nbit
cdef float[::1] output_pixel_rgb
@ -228,20 +311,27 @@ def dither_image(screen, float[:, :, ::1] image_rgb, dither, int lookahead, unsi
for i in range(3):
input_pixel_rgb[i] = image_rgb[y,x,i]
if lookahead:
# Compute all possible 2**N choices of n-bit pixel colours for positions x .. x + lookahead
lookahead_palette_choices_nbit = lookahead_options(screen, lookahead, output_pixel_nbit, x % 4)
# Apply error diffusion for each of these 2**N choices, and compute which produces the closest match
# to the source image over the succeeding N pixels
best_idx = dither_lookahead(
&cdither, palette_rgb, image_rgb, x, y, lookahead_palette_choices_nbit, lookahead, distances,
xres)
output_pixel_nbit = lookahead_palette_choices_nbit[best_idx, 0]
else:
palette_choices_nbit, palette_choices_rgb = screen.pixel_palette_options(output_pixel_nbit, x)
output_pixel_nbit = find_nearest_colour(
input_pixel_rgb, palette_choices_nbit, palette_choices_rgb, distances)
# Choose the closest colour among the available n-bit palette options
palette_choices_nbit = screen.pixel_palette_options(output_pixel_nbit, x)
output_pixel_nbit = find_nearest_colour(input_pixel_rgb, palette_choices_nbit, distances)
# Apply error diffusion from chosen output pixel value
output_pixel_rgb = palette_rgb[output_pixel_nbit]
for i in range(3):
quant_error[i] = input_pixel_rgb[i] - output_pixel_rgb[i]
image_nbit[y, x] = output_pixel_nbit
apply(&cdither, xres, yres, x, y, image_rgb, quant_error)
for i in range(3):
image_rgb[y, x, i] = output_pixel_rgb[i]

13
screen.py
View File

@ -120,9 +120,7 @@ class DHGR140Screen(Screen):
def pixel_palette_options(self, last_pixel_nbit, x: int):
# All 16 colour choices are available at every x position.
return (
np.array(list(self.palette.RGB.keys()), dtype=np.uint8),
np.array(list(self.palette.RGB.values()), dtype=np.uint8))
return np.array(list(self.palette.RGB.keys()), dtype=np.uint8)
class DHGR560Screen(Screen):
@ -150,9 +148,7 @@ class DHGR560Screen(Screen):
other_dots[x % 4] = not other_dots[x % 4]
other_dots = tuple(other_dots)
other_pixel_nbit = self.palette.DOTS_TO_INDEX[other_dots]
return (np.array([last_pixel_nbit, other_pixel_nbit], dtype=np.uint8),
np.array([self.palette.RGB[last_pixel_nbit],
self.palette.RGB[other_pixel_nbit]], dtype=np.uint8))
return np.array([last_pixel_nbit, other_pixel_nbit], dtype=np.uint8)
# TODO: refactor to share implementation with DHGR560Screen
@ -202,10 +198,7 @@ class DHGR560NTSCScreen(Screen):
next_dots1[x % 4 + 4] = True
pixel_nbit_0 = self.palette.DOTS_TO_INDEX[tuple(next_dots0)]
pixel_nbit_1 = self.palette.DOTS_TO_INDEX[tuple(next_dots1)]
return (
np.array([pixel_nbit_0, pixel_nbit_1], dtype=np.uint8),
np.array([self.palette.RGB[pixel_nbit_0],
self.palette.RGB[pixel_nbit_1]], dtype=np.uint8))
return np.array([pixel_nbit_0, pixel_nbit_1], dtype=np.uint8)
def bitmap_to_ntsc(self, bitmap: np.ndarray) -> np.ndarray:
y_width = 12