WebP/Lossy: Add a missing clamp

The spec says that the AC dequantization factor for Y2 data should
be at least 8, so do that.

This only has a very small effect (only the first two AC table
entries are < 8 after multiplying with 155 / 100, so this would
have only a small effect on brightness), and this case is hit
exactly 0 times in all my test images.  But it's still good to match
the spec.

1 files changed, 2 insertions, 2 deletions

diff --git a/Userland/Libraries/LibGfx/ImageFormats/WebPLoaderLossy.cpp b/Userland/Libraries/LibGfx/ImageFormats/WebPLoaderLossy.cpp
index 0714f94e57..811620fdbd 100644
--- a/Userland/Libraries/LibGfx/ImageFormats/WebPLoaderLossy.cpp
+++ b/Userland/Libraries/LibGfx/ImageFormats/WebPLoaderLossy.cpp
@@ -609,7 +609,7 @@ i16 dequantize_value(i16 value, bool is_dc, QuantizationIndices const& quantizat
     //  can be found in related lookup functions in dixie.c (Section 20.4)."
     // Apparently spec writing became too much work at this point. In section 20.4, in dequant_init():
     // * For y2, the output (!) of dc_qlookup is multiplied by 2, the output of ac_qlookup is multiplied by 155 / 100
-    // * Also for y2, ac_qlookup is at least 8 for lower table entries (XXX!)
+    // * Also for y2, ac_qlookup is at least 8 for lower table entries
     // * For uv, the dc_qlookup index is clamped to 117 (instead of 127 for everything else)
     //   (or, alternatively, the value is clamped to 132 at most)
 
@@ -646,7 +646,7 @@ i16 dequantize_value(i16 value, bool is_dc, QuantizationIndices const& quantizat
         if (is_dc)
             dequantization_factor *= 2;
         else
-            dequantization_factor = (dequantization_factor * 155) / 100;
+            dequantization_factor = max((dequantization_factor * 155) / 100, 8);
     }
 
     return dequantization_factor * value;