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stb_image: JPEG: Convert RGB to grayscale properly

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This commit is contained in:
Jeremy Sawicki 2017-03-02 18:06:10 -08:00
parent 59a5a155b4
commit 552c548a0e
1 changed files with 14 additions and 6 deletions
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20
stb_image.h
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@ -3596,7 +3596,7 @@ static stbi_uc *load_jpeg_image(stbi__jpeg *z, int *out_x, int *out_y, int *comp
// determine actual number of components to generate // determine actual number of components to generate
n = req_comp ? req_comp : z->s->img_n; n = req_comp ? req_comp : z->s->img_n;
if (z->s->img_n == 3 && n < 3) if (z->s->img_n == 3 && n < 3 && z->rgb != 3)
decode_n = 1; decode_n = 1;
else else
decode_n = z->s->img_n; decode_n = z->s->img_n;
@ -3674,11 +3674,19 @@ static stbi_uc *load_jpeg_image(stbi__jpeg *z, int *out_x, int *out_y, int *comp
out += n; out += n;
} }
} else { } else {
stbi_uc *y = coutput[0]; if (z->rgb == 3) {
if (n == 1) for (i=0; i < z->s->img_x; ++i) {
for (i=0; i < z->s->img_x; ++i) out[i] = y[i]; out[0] = stbi__compute_y(coutput[0][i], coutput[1][i], coutput[2][i]);
else out[1] = 255;
for (i=0; i < z->s->img_x; ++i) *out++ = y[i], *out++ = 255; out += n;
}
} else {
stbi_uc *y = coutput[0];
if (n == 1)
for (i=0; i < z->s->img_x; ++i) out[i] = y[i];
else
for (i=0; i < z->s->img_x; ++i) *out++ = y[i], *out++ = 255;
}
} }
} }
stbi__cleanup_jpeg(z); stbi__cleanup_jpeg(z);