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recognize greys in 8-color quantization

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nick black 2021-07-08 23:37:07 -04:00
parent a7779c5024
commit b96dc6d1bc
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GPG Key ID: 5F43400C21CBFACC
3 changed files with 25 additions and 2 deletions
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21
src/lib/internal.h
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@ -497,6 +497,21 @@ nfbcellidx(const ncplane* n, int row, int col){
return fbcellidx(logical_to_virtual(n, row), n->lenx, col);
}
// is the rgb value greyish (excluding white and black)?
static inline bool
rgb_greyish_p(unsigned r, unsigned g, unsigned b){
const unsigned GREYMASK = 0xf8;
if((r & GREYMASK) == (g & GREYMASK) && (g & GREYMASK) == (b & GREYMASK)){
if(r < 16){
return false; // black
}else if(r > 240){
return false; // white
}
return true;
}
return false;
}
// For our first attempt, O(1) uniform conversion from 8-bit r/g/b down to
// ~2.4-bit 6x6x6 cube + greyscale (assumed on entry; I know no way to
// even semi-portably recover the palette) proceeds via: map each 8-bit to
@ -504,10 +519,9 @@ nfbcellidx(const ncplane* n, int row, int col){
// otherwise, c / 42.7 to map to 6 values.
static inline int
rgb_quantize_256(unsigned r, unsigned g, unsigned b){
const unsigned GREYMASK = 0xf8;
// if all 5 MSBs match, return grey from 24-member grey ramp or pure
// black/white from original 16 (0 and 15, respectively)
if((r & GREYMASK) == (g & GREYMASK) && (g & GREYMASK) == (b & GREYMASK)){
if(rgb_greyish_p(r, g, b)){
// 256 / 26 == 9.846
int gidx = r * 5 / 49 - 1;
if(gidx < 0){
@ -536,6 +550,9 @@ rgb_quantize_8(unsigned r, unsigned g, unsigned b){
static const int MAGENTA = 5;
static const int CYAN = 6;
static const int WHITE = 7;
if(rgb_greyish_p(r, g, b)){
return WHITE;
}
if(r < 128){ // we have no red
if(g < 128){ // we have no green
if(b < 128){

3
src/poc/cjkscroll.c
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@ -17,6 +17,9 @@ int main(void){
struct ncplane* n = notcurses_stddim_yx(nc, &dimy, &dimx);
wchar_t wc = 0x4e00;
ncplane_set_scrolling(n, true);
ncplane_set_styles(n, NCSTYLE_BOLD);
ncplane_putstr(n, "This program is *not* indicative of real scrolling speed.\n");
ncplane_set_styles(n, NCSTYLE_NONE);
while(true){
struct timespec req = { .tv_sec = 0, .tv_nsec = 1000000, };
nanosleep(&req, NULL);

3
src/poc/scroll.c
View File

@ -16,6 +16,9 @@ int main(void){
struct ncplane* n = notcurses_stddim_yx(nc, &dimy, &dimx);
char c = 'A';
ncplane_set_scrolling(n, true);
ncplane_set_styles(n, NCSTYLE_BOLD);
ncplane_putstr(n, "This program is *not* indicative of real scrolling speed.\n");
ncplane_set_styles(n, NCSTYLE_NONE);
while(true){
struct timespec req = { .tv_sec = 0, .tv_nsec = 1000000, };
nanosleep(&req, NULL);