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Fix: 24 bit image with non-zero alpha mask treated fine (#1457)

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* bytes per pixel

* Fix alpha condition

* has_alpha logic

* Fixes condition bpp

* Minor
This commit is contained in:
Victor Sokolov
2025-07-11 16:08:56 +04:00
committed by GitHub
parent c3eb1b9633
commit 61f08c20ac
1 changed files with 16 additions and 11 deletions
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27
vips/bmpload.c
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@@ -32,7 +32,8 @@ typedef struct _VipsForeignLoadBmp {
uint32_t num_colors;
int bands;
int bands; // target image bands
int bytes_per_pixel; // source image bytes per pixel (not used when bpp<8)
bool top_down; // true if image is vertically reversed
bool rle; // true if image is compressed with RLE
@@ -201,20 +202,23 @@ vips_foreign_load_bmp_header(VipsForeignLoad *load)
int bands = 3; // 3 bands by default (RGB)
// Let's determine if the image has an alpha channel
bool has_alpha = FALSE;
bool has_alpha = bpp == 32;
// If the info header is V4 or V5, check for alpha channel explicitly
if (info_header_len > BMP_BITMAP_INFO_HEADER_LEN) {
// If the info header is V4 or V5, check for alpha channel mask explicitly.
// If it's non-zero, then the target image should have an alpha channel.
if ((has_alpha) && (info_header_len > BMP_BITMAP_INFO_HEADER_LEN)) {
has_alpha = GUINT32_FROM_LE(*(uint32_t *) (info_header + 48)) != 0;
}
else {
has_alpha = (bpp == 32); // otherwise, rely on the bpp value
}
// Target image should have alpha channel only in case source image has alpha channel
// AND source image alpha mask is not zero
if (has_alpha) {
bands = 4;
}
// Source image bytes per pixel. It does not depend on the alpha mask, just on the bpp.
int bytes_per_pixel = bpp >= 8 ? bpp / 8 : 1; // bytes per pixel in the source image
if (height < 0) {
height = -height;
top_down = TRUE;
@@ -332,6 +336,7 @@ vips_foreign_load_bmp_header(VipsForeignLoad *load)
bmp->bmask = bmask;
bmp->amask = amask;
bmp->bytes_per_pixel = bytes_per_pixel;
bmp->y_pos = 0;
bmp->dx = 0; // In sequential access this indicates that we need to skip n lines
@@ -360,7 +365,7 @@ static int
vips_foreign_load_bmp_24_32_generate_strip(VipsRect *r, VipsRegion *out_region, VipsForeignLoadBmp *bmp)
{
// Align the row size to 4 bytes, as BMP rows are 4-byte aligned.
int row_size = (bmp->bands * r->width + 3) & (~3);
int row_size = (bmp->bytes_per_pixel * r->width + 3) & (~3);
VipsPel *src;
VipsPel *dest;
@@ -385,7 +390,7 @@ vips_foreign_load_bmp_24_32_generate_strip(VipsRect *r, VipsRegion *out_region,
}
dest += bmp->bands;
src += bmp->bands;
src += bmp->bytes_per_pixel;
}
bmp->y_pos += 1;
@@ -401,7 +406,7 @@ static int
vips_foreign_load_bmp_16_generate_strip(VipsRect *r, VipsRegion *out_region, VipsForeignLoadBmp *bmp)
{
// Align the row size to 4 bytes, as BMP rows are 4-byte aligned, 16 bpp = 2 bytes per pixel
int row_size = (2 * r->width + 3) & (~3);
int row_size = (bmp->bytes_per_pixel * r->width + 3) & (~3);
VipsPel *src;
VipsPel *dest;
@@ -424,7 +429,7 @@ vips_foreign_load_bmp_16_generate_strip(VipsRect *r, VipsRegion *out_region, Vip
dest[2] = (uint8_t) (pixel & bmp->bmask) << 3;
dest += bmp->bands;
src += 2; // 2 bytes per pixel for 16 bpp
src += bmp->bytes_per_pixel; // 2 bytes per pixel for 16 bpp
}
bmp->y_pos += 1;