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Modification to resolution handling in TIFF reader / writer #4185

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Modification to resolution handling in TIFF reader / writer #4185

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54b203b
Modified TIFF reader to set resolution to zero if no resolution set w…
ruven Oct 6, 2024
0034ff8
Resolution only set when saving as PNG if resolution is really known
ruven Oct 6, 2024
86c49c3
Made default X/Y resolution zero for Vips images rather than 1.0
ruven Oct 6, 2024
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4 changes: 2 additions & 2 deletions libvips/foreign/tiff2vips.c
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Original file line number Diff line number Diff line change
Expand Up @@ -541,8 +541,8 @@ get_resolution(TIFF *tiff, VipsImage *out)
/* We used to warn about missing res data, but it happens so
* often and is so harmless, why bother.
*/
x = 1.0;
y = 1.0;
x = 0.0;
y = 0.0;
}

out->Xres = x;
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14 changes: 8 additions & 6 deletions libvips/foreign/vips2tiff.c
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Original file line number Diff line number Diff line change
@@ -1,4 +1,4 @@
/* TIFF PARTS:

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Run clang-format on libvips/foreign/vips2tiff.c 

File libvips/foreign/vips2tiff.c does not conform to Custom style guidelines. (lines 890, 894, 895)
* Copyright (c) 1988, 1990 by Sam Leffler.
* All rights reserved.
*
Expand Down Expand Up @@ -885,13 +885,15 @@
!wtiff->tile)
wtiff->we_compress = FALSE;

/* Don't write mad resolutions (eg. zero), it confuses some programs.
/* Only set resolution if we actually have one. Also, mad resolutions (eg. zero) confuse some programs.
*/
TIFFSetField(tif, TIFFTAG_RESOLUTIONUNIT, wtiff->resunit);
TIFFSetField(tif, TIFFTAG_XRESOLUTION,
VIPS_FCLIP(0.01, wtiff->xres, 1000000));
TIFFSetField(tif, TIFFTAG_YRESOLUTION,
VIPS_FCLIP(0.01, wtiff->yres, 1000000));
if(wtiff->xres || wtiff->yres){
TIFFSetField(tif, TIFFTAG_RESOLUTIONUNIT, wtiff->resunit);
/* Scale resolution by the subsampling factor of the current level
*/
if(wtiff->xres) TIFFSetField(tif, TIFFTAG_XRESOLUTION, (wtiff->xres/layer->sub));
if(wtiff->yres) TIFFSetField(tif, TIFFTAG_YRESOLUTION, (wtiff->yres/layer->sub));
}

if (wtiff_embed_xmp(wtiff, tif) ||
wtiff_embed_iptc(wtiff, tif) ||
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10 changes: 6 additions & 4 deletions libvips/foreign/vipspng.c
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@@ -1,4 +1,4 @@
/* Load/save png image with libpng

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File libvips/foreign/vipspng.c does not conform to Custom style guidelines. (lines 1168, 1169, 1170)
*
* 28/11/03 JC
* - better no-overshoot on tile loop
Expand Down Expand Up @@ -1163,11 +1163,13 @@
in->Xsize, in->Ysize, bitdepth, color_type, interlace_type,
PNG_COMPRESSION_TYPE_DEFAULT, PNG_FILTER_TYPE_DEFAULT);

/* Set resolution. libpng uses pixels per meter.
/* Set resolution if known. libpng uses pixels per meter.
*/
png_set_pHYs(write->pPng, write->pInfo,
VIPS_RINT(in->Xres * 1000), VIPS_RINT(in->Yres * 1000),
PNG_RESOLUTION_METER);
if(in->Xres && in->Yres){
png_set_pHYs(write->pPng, write->pInfo,
VIPS_RINT(in->Xres * 1000), VIPS_RINT(in->Yres * 1000),
PNG_RESOLUTION_METER);
}

/* Metadata
*/
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4 changes: 2 additions & 2 deletions libvips/iofuncs/image.c
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Expand Up @@ -1344,8 +1344,8 @@ vips_image_init(VipsImage *image)
image->Ysize = 1;
image->Bands = 1;

image->Xres = 1.0;
image->Yres = 1.0;
image->Xres = 0.0;
image->Yres = 0.0;

image->fd = -1; /* since 0 is stdout */
image->sslock = vips_g_mutex_new();
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