updated expressions logic per feedback

Signed-off-by: Lydia Zheng <[email protected]>

Author: lydia-zheng

src/doc/oiiotool.rst

@@ -163,7 +163,9 @@ contents of an expression may be any of:
     information from when the file was read from disk.
   * `STATS` : a multi-line string containing the image statistics that would
     be printed with `oiiotool -stats`.
-
+  * `IS_CONSTANT`: metadata to check if the image pixels are of constant color, returns 1 if true, and 0 if false.
+  * `IS_BLACK`: metadata to check if the image pixels are all black, a subset of IS_CONSTANT. Also returns 1 if true, and 0 if false.
+  
 * *imagename.'metadata'*
 
   If the metadata name is not a "C identifier" (initial letter followed by

src/oiiotool/expressions.cpp

@@ -317,6 +317,32 @@ Oiiotool::express_parse_atom(const string_view expr, string_view& s,
                 result = out.str();
                 if (result.size() && result.back() == '\n')
                     result.pop_back();
+
+            } else if (metadata == "IS_CONSTANT") {
+                std::vector<float> color((*img)(0, 0).nchannels());
+                if (ImageBufAlgo::isConstantColor((*img)(0, 0), 0.0f, color)) {
+                    result = "1";
+                } else {
+                    result = "0";
+                }
+
+
+            } else if (metadata == "IS_BLACK") {
+                std::vector<float> color((*img)(0, 0).nchannels());
+                // Check constant first to guard against false positive average of 0 with negative values i.e. -2, 1, 1
+                if (ImageBufAlgo::isConstantColor((*img)(0, 0), 0.0f, color)) {
+                    // trusting that the constantcolor check means all channels have the same value, so we only check the first channel
+                    if (color[0] == 0.0f) {
+                        result = "1";
+                    }
+                    else {
+                        result = "0";
+                    }
+                } else {
+                    // Not even constant color case -> We don't want those to count as black frames.
+                    result = "0";
+                }
+
             } else if (using_bracket) {
                 // For the TOP[meta] syntax, if the metadata doesn't exist,
                 // return the empty string, and do not make an error.