feat(oiiotool): oiiotool new expression eval tokens IS_CONSTANT, IS_BLACK

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 +317,28 @@ 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.

testsuite/oiiotool-control/ref/out.txt

@@ -326,6 +326,10 @@ TOP = ../common/grid.tif, BOTTOM = ../common/tahoe-tiny.tif
 Stack holds [1] = ../common/tahoe-small.tif
 filename=../common/tahoe-tiny.tif file_extension=.tif file_noextension=../common/tahoe-tiny
 MINCOLOR=0,0,0 MAXCOLOR=0.745098,1,1 AVGCOLOR=0.101942,0.216695,0.425293
+Testing expressions IS_BLACK, IS_CONSTANT:
+  grey is-black? 0 is-constant? 1
+  black is-black? 1 is-constant? 1
+  gradient is-black? 0 is-constant? 0
 Testing NIMAGES:
   0
   1

testsuite/oiiotool-control/run.py

@@ -183,6 +183,14 @@
                      "--echo \"filename={TOP.filename} file_extension={TOP.file_extension} file_noextension={TOP.file_noextension}\" " +
                      "--echo \"MINCOLOR={TOP.MINCOLOR} MAXCOLOR={TOP.MAXCOLOR} AVGCOLOR={TOP.AVGCOLOR}\"")
 
+command += oiiotool ("--echo \"Testing expressions IS_BLACK, IS_CONSTANT:\" " +
+                     "--pattern:type=uint16 constant:color=0.5,0.5,0.5 4x4 3 " +
+                     "--echo \"  grey is-black? {TOP.IS_BLACK} is-constant? {TOP.IS_CONSTANT}\" " +
+                     "--pattern:type=uint16 constant:color=0,0,0 4x4 3 " +
+                     "--echo \"  black is-black? {TOP.IS_BLACK} is-constant? {TOP.IS_CONSTANT}\" " +
+                     "--pattern:type=uint16 fill:left=0,0,0:right=1,1,1 4x4 3 " +
+                     "--echo \"  gradient is-black? {TOP.IS_BLACK} is-constant? {TOP.IS_CONSTANT}\" "
+                    )
 command += oiiotool (
     "--echo \"Testing NIMAGES:\" " +
     "--echo \"  {NIMAGES}\" " +