From 6ab93935a7f886c202fc996747b1ade18aacc8d8 Mon Sep 17 00:00:00 2001
From: Andrew Murray <radarhere@users.noreply.github.com>
Date: Tue, 15 Apr 2025 22:35:12 +1000
Subject: [PATCH 1/2] Simplified code

---
 src/PIL/SgiImagePlugin.py | 28 ++++++----------------------
 1 file changed, 6 insertions(+), 22 deletions(-)

diff --git a/src/PIL/SgiImagePlugin.py b/src/PIL/SgiImagePlugin.py
index 44254b7a4..b1f57742e 100644
--- a/src/PIL/SgiImagePlugin.py
+++ b/src/PIL/SgiImagePlugin.py
@@ -82,17 +82,10 @@ class SgiImageFile(ImageFile.ImageFile):
         # zsize : channels count
         zsize = i16(s, 10)
 
-        # layout
-        layout = bpc, dimension, zsize
-
         # determine mode from bits/zsize
-        rawmode = ""
         try:
-            rawmode = MODES[layout]
+            rawmode = MODES[(bpc, dimension, zsize)]
         except KeyError:
-            pass
-
-        if rawmode == "":
             msg = "Unsupported SGI image mode"
             raise ValueError(msg)
 
@@ -156,24 +149,15 @@ def _save(im: Image.Image, fp: IO[bytes], filename: str | bytes) -> None:
     # Run-Length Encoding Compression - Unsupported at this time
     rle = 0
 
-    # Number of dimensions (x,y,z)
-    dim = 3
     # X Dimension = width / Y Dimension = height
     x, y = im.size
-    if im.mode == "L" and y == 1:
-        dim = 1
-    elif im.mode == "L":
-        dim = 2
     # Z Dimension: Number of channels
     z = len(im.mode)
-
-    if dim in {1, 2}:
-        z = 1
-
-    # assert we've got the right number of bands.
-    if len(im.getbands()) != z:
-        msg = f"incorrect number of bands in SGI write: {z} vs {len(im.getbands())}"
-        raise ValueError(msg)
+    # Number of dimensions (x,y,z)
+    if im.mode == "L":
+        dim = 1 if y == 1 else 2
+    else:
+        dim = 3
 
     # Minimum Byte value
     pinmin = 0

From 06b50389b034c4cb462366b128f7640890d48c25 Mon Sep 17 00:00:00 2001
From: Andrew Murray <radarhere@users.noreply.github.com>
Date: Tue, 15 Apr 2025 22:49:24 +1000
Subject: [PATCH 2/2] Test opening and saving errors

---
 Tests/test_file_sgi.py | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/Tests/test_file_sgi.py b/Tests/test_file_sgi.py
index da0965fa1..abf424dbf 100644
--- a/Tests/test_file_sgi.py
+++ b/Tests/test_file_sgi.py
@@ -1,5 +1,6 @@
 from __future__ import annotations
 
+from io import BytesIO
 from pathlib import Path
 
 import pytest
@@ -71,6 +72,15 @@ def test_invalid_file() -> None:
         SgiImagePlugin.SgiImageFile(invalid_file)
 
 
+def test_unsupported_image_mode() -> None:
+    with open("Tests/images/hopper.rgb", "rb") as fp:
+        data = fp.read()
+    data = data[:3] + b"\x03" + data[4:]
+    with pytest.raises(ValueError, match="Unsupported SGI image mode"):
+        with Image.open(BytesIO(data)):
+            pass
+
+
 def roundtrip(img: Image.Image, tmp_path: Path) -> None:
     out = tmp_path / "temp.sgi"
     img.save(out, format="sgi")
@@ -109,3 +119,11 @@ def test_unsupported_mode(tmp_path: Path) -> None:
 
     with pytest.raises(ValueError):
         im.save(out, format="sgi")
+
+
+def test_unsupported_number_of_bytes_per_pixel(tmp_path: Path) -> None:
+    im = hopper()
+    out = tmp_path / "temp.sgi"
+
+    with pytest.raises(ValueError, match="Unsupported number of bytes per pixel"):
+        im.save(out, bpc=3)