oiiotool: -i:native=1, fix --native behavior, fix convert datatype (#4708)

A constellation of closely related fixes and additions related to
oiiotool `-i` behavior:

* When using `-i:now=1` to force for immediate read rather than using an
ImageCache, it would "forget" any prior setting of `--native`. This is
fixed now to correctly combine desire for bypassing the cache with
hinting to maintain native data type.

* When restricting channel subset with `-i:ch=...`, use of the
`--native` flag was incorrect in some cases -- it would use the overall
best single data format of all channels, rather than restricting that to
the selected channel range. So, for example, if you said `-i:ch=R,G,B,A`
and those channels were all `half`, but channel 17 (not selected) was
`float`, you would get a conversion to float rather than keeping the
selected channels at their native half. The solution here is that the
type chosen for `--native` behavior should only consider the selected
channel subset, not all channels.

* Add a new `-i` modifier: `:native=1`, allowing you to select the
"native" behavior on a per-input-file basis (the existing `--native`
command sets the default).

Signed-off-by: Larry Gritz <lg@larrygritz.com>

Author: lgritz

src/doc/oiiotool.rst

@@ -1180,8 +1180,13 @@ Reading images
 
     Optional appended modifiers include:
 
+      `:native=` *int*
+        If nonzero, read the image in as close as possible to its "native"
+        format, versus oiiotool's default of converting all images to float
+        internally. This also turns on "now". (Added in release 3.0.6.0.)
       `:now=` *int*
-        If 1, read the image now, before proceeding to the next command.
+        If nonzero, read the image now, before proceeding to the next command
+        (bypassing the ImageCache, even for big images).
       `:autocc=` *int*
         Enable or disable `--autocc` for this input image (the default is to use
         the global setting).

src/oiiotool/imagerec.cpp

@@ -335,8 +335,16 @@ ImageRec::read(ReadPolicy readpolicy, string_view channel_set)
                 if (m_input_dataformat != ib->nativespec().format)
                     m_subimages[s].m_was_direct_read = false;
                 forceread = true;
-            } else if (readpolicy & ReadNative)
-                convert = ib->nativespec().format;
+            } else if (readpolicy & ReadNative) {
+                if (channel_set.size()) {
+                    convert = TypeUnknown;
+                    for (int c = chbegin; c < chend; ++c)
+                        convert = TypeDesc::basetype_merge(
+                            convert, ib->nativespec().channelformat(c));
+                } else {
+                    convert = ib->nativespec().format;
+                }
+            }
             if (!forceread && convert != TypeDesc::UINT8
                 && convert != TypeDesc::UINT16 && convert != TypeDesc::HALF
                 && convert != TypeDesc::FLOAT) {

src/oiiotool/oiiotool.cpp

@@ -5176,6 +5176,7 @@ input_file(Oiiotool& ot, cspan<const char*> argv)
     auto fileoptions     = ot.extract_options(command);
     int printinfo        = fileoptions.get_int("info", ot.printinfo);
     bool readnow         = fileoptions.get_int("now", 0);
+    bool native          = fileoptions.get_int("native", int(ot.nativeread));
     bool autocc          = fileoptions.get_int("autocc", ot.autocc);
     bool autoccunpremult = fileoptions.get_int("unpremult", ot.autoccunpremult);
     std::string infoformat = fileoptions.get_string("infoformat",
@@ -5261,6 +5262,7 @@ input_file(Oiiotool& ot, cspan<const char*> argv)
             ot.input_channel_set = channel_set;
             readnow              = true;
         }
+        readnow |= native;
 
         if (substitute) {
             ot.push(ImageRecRef(new ImageRec(substitute)));
@@ -5273,9 +5275,10 @@ input_file(Oiiotool& ot, cspan<const char*> argv)
             if (ot.input_config_set)
                 ot.curimg->configspec(ot.input_config);
             ot.curimg->input_dataformat(input_dataformat);
-            if (readnow)
-                ot.read(ReadNoCache, channel_set);
-            else
+            if (readnow) {
+                ReadPolicy policy = native ? ReadNativeNoCache : ReadNoCache;
+                ot.read(policy, channel_set);
+            } else
                 ot.read_nativespec();
             if (ot.first_input_dimensions.format == TypeUnknown) {
                 ot.first_input_dimensions.copy_dimensions(
@@ -6561,7 +6564,7 @@ Oiiotool::getargs(int argc, char* argv[])
 
     ap.separator("Commands that read images:");
     ap.arg("-i %s:FILENAME")
-      .help("Input file (options: autocc=, ch=, info=, infoformat=, now=, type=, unpremult=)")
+      .help("Input file (options: autocc=, ch=, info=, infoformat=, native=, now=, type=, unpremult=)")
       .OTACTION(input_file);
     ap.arg("--iconfig %s:NAME %s:VALUE")
       .help("Sets input config attribute (options: type=...)")