Implement Header Sniffing For Magickload Tga (#2533)

Add TGA sniffing

libvips/foreign/magick.c

@@ -52,12 +52,24 @@
 
 #if defined(HAVE_MAGICK6) || defined(HAVE_MAGICK7)
 
-/* ImageMagick can't detect some formats, like ICO, by examining the contents --
+/* ImageMagick can't detect some formats, like ICO and TGA, by examining the contents --
- * ico.c simply does not have a recogniser.
+ * ico.c and tga.c simply do not have recognisers.
  *
  * For these formats, do the detection ourselves.
- *
  * Return an IM format specifier, or NULL to let IM do the detection.
+ *
+ * For sniffing TGAs, we check that there is at least enough room for the header and that
+ * the preamble contains valid values:
+ * -----------------------------------------------------------
+ * |0x00 | 0-255 idlength, skip                              |
+ * |0x01 | 0-1, color map present                            |
+ * |0x02 | Any of (0, 1, 2, 3, 9, 10, 11), Image type        |
+ * -----------------------------------------------------------
+ *
+ * References:
+ * * https://www.dca.fee.unicamp.br/~martino/disciplinas/ea978/tgaffs.pdf
+ * * http://www.paulbourke.net/dataformats/tga/
+ * * https://en.wikipedia.org/wiki/Truevision_TGA#Technical_details
  */
 static const char *
 magick_sniff( const unsigned char *bytes, size_t length )
@@ -68,6 +80,16 @@ magick_sniff( const unsigned char *bytes, size_t length )
 		bytes[2] == 1 &&
 		bytes[3] == 0 )
 		return( "ICO" );
+  if( length >= 18 &&
+    (bytes[1] == 0 || bytes[1] == 1) && (
+    bytes[2] == 0  ||
+    bytes[2] == 1  ||
+    bytes[2] == 2  ||
+    bytes[2] == 3  ||
+    bytes[2] == 9  ||
+    bytes[2] == 10 ||
+    bytes[2] == 11) )
+    return( "TGA" );
 
 	return( NULL );
 }

test/test-suite/helpers/helpers.py

@@ -41,6 +41,8 @@ DICOM_FILE = os.path.join(IMAGES, "dicom_test_image.dcm")
 BMP_FILE = os.path.join(IMAGES, "MARBLES.BMP")
 NIFTI_FILE = os.path.join(IMAGES, "avg152T1_LR_nifti.nii.gz")
 ICO_FILE = os.path.join(IMAGES, "favicon.ico")
+TGA_FILE = os.path.join(IMAGES, "targa.tga")
+SGI_FILE = os.path.join(IMAGES, "silicongraphics.sgi")
 AVIF_FILE = os.path.join(IMAGES, "avif-orientation-6.avif")
 HEIC_FILE = os.path.join(IMAGES, "heic-orientation-6.heic")
 RGBA_FILE = os.path.join(IMAGES, "rgba.png")

test/test-suite/test_foreign.py

@@ -10,7 +10,7 @@ from helpers import \
     JPEG_FILE, SRGB_FILE, MATLAB_FILE, PNG_FILE, TIF_FILE, OME_FILE, \
     ANALYZE_FILE, GIF_FILE, WEBP_FILE, EXR_FILE, FITS_FILE, OPENSLIDE_FILE, \
     PDF_FILE, SVG_FILE, SVGZ_FILE, SVG_GZ_FILE, GIF_ANIM_FILE, DICOM_FILE, \
-    BMP_FILE, NIFTI_FILE, ICO_FILE, AVIF_FILE, TRUNCATED_FILE, \
+    BMP_FILE, NIFTI_FILE, ICO_FILE, TGA_FILE, SGI_FILE, AVIF_FILE, TRUNCATED_FILE, \
     GIF_ANIM_EXPECTED_PNG_FILE, GIF_ANIM_DISPOSE_BACKGROUND_FILE, \
     GIF_ANIM_DISPOSE_BACKGROUND_EXPECTED_PNG_FILE, \
     GIF_ANIM_DISPOSE_PREVIOUS_FILE, \
@@ -664,6 +664,22 @@ class TestForeign:
         assert im.width == 16
         assert im.height == 16
 
+        # libvips has its own sniffer for TGA, test that
+        with open(TGA_FILE, 'rb') as f:
+            buf = f.read()
+        im = pyvips.Image.new_from_buffer(buf, "")
+        assert im.width == 433
+        assert im.height == 433
+
+        # Test SGI/RGB files to sanity check that sniffers 
+        # aren't too broad
+        with open(SGI_FILE, 'rb') as f:
+            buf = f.read()
+        im = pyvips.Image.new_from_buffer(buf, "")
+        assert im.width == 433
+        assert im.height == 433
+        
+
         # load should see metadata like eg. icc profiles 
         im = pyvips.Image.magickload(JPEG_FILE)
         assert len(im.get("icc-profile-data")) == 564