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imageviewer: jpegp: improve downscale quality

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Use simple area-averaging for smoother images.

Change-Id: I7ac2db05262500041286404c97a615e4b3a43194
This commit is contained in:
Roman Artiukhin 2025-12-31 19:21:56 +02:00 • committed by Solomon Peachy
parent 64e0ced696
commit 7d067ca798
1 changed files with 32 additions and 3 deletions
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35
apps/plugins/imageviewer/jpegp/jpegp.c
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@ -229,9 +229,38 @@ static int get_image(struct image_info *info, int frame, int ds)
j->Components[2].du[j->Components[2].du_width * ((y / v2) / 8)] + 8 * ((y / v2) & 7);
for (x = 0; x < max_x; x += ds)
{
TCOEF c0 = C0[(x / h0 / 8) * 64 + ((x / h0) & 7)];
TCOEF c1 = C1[(x / h1 / 8) * 64 + ((x / h1) & 7)];
TCOEF c2 = C2[(x / h2 / 8) * 64 + ((x / h2) & 7)];
int c0, c1, c2;
if (ds == 1)
{
c0 = C0[(x / h0 / 8) * 64 + ((x / h0) & 7)];
c1 = C1[(x / h1 / 8) * 64 + ((x / h1) & 7)];
c2 = C2[(x / h2 / 8) * 64 + ((x / h2) & 7)];
}
else
{
/* Box filter downsampling (area averaging):
Average a ds*ds block of Y/U/V samples per output pixel
for simple anti-aliasing without extra buffers */
int sumY = 0, sumU = 0, sumV = 0;
int dx, dy;
int area = ds * ds;
for (dy = 0; dy < ds; dy++)
{
TCOEF *C0_dy = j->Components[0].du[j->Components[0].du_width * (((y + dy) / v0) / 8)] + 8 * (((y + dy) / v0) & 7);
TCOEF *C1_dy = j->Components[1].du[j->Components[1].du_width * (((y + dy) / v1) / 8)] + 8 * (((y + dy) / v1) & 7);
TCOEF *C2_dy = j->Components[2].du[j->Components[2].du_width * (((y + dy) / v2) / 8)] + 8 * (((y + dy) / v2) & 7);
for (dx = 0; dx < ds; dx++)
{
int sx = x + dx;
sumY += C0_dy[((sx / h0 / 8) * 64) + ((sx / h0) & 7)];
sumU += C1_dy[((sx / h1 / 8) * 64) + ((sx / h1) & 7)];
sumV += C2_dy[((sx / h2 / 8) * 64) + ((sx / h2) & 7)];
}
}
c0 = (sumY + area/2) / area;
c1 = (sumU + area/2) / area;
c2 = (sumV + area/2) / area;
}
// ITU BT.601 full-range YUV-to-RGB integer approximation
{