NDPluginPvxs does not use the correct ScalerType enum when for the codec.parameters value when sending compressed NDArrays

[MarkRivers]

NDPluginPvxs does not work with ImageJ when the NDArrays are compressed. ImageJ reports the following errors:

31-Dec-2025 12:30:51.982: handleEvents caught exception java.lang.NullPointerException

and the images do not update.

This is the output of pvget, which does have the data and report the correct compression.

(base) [epics@corvette ADSimDetector]$ pvget 13SIM1:Pva1:Image
13SIM1:Pva1:Image epics:nt/NTNDArray:1.0
    union value
        ubyte[]  [0,0,2,164,31,85,1,0,108,31,170,1,0,108,15,255,0,108,31,85,255,0,108,15,0,1,255,239,31,153,1,0,108,31,204,1,0,108,31,102,1,0,108,31,51,
1,0,108,15,255,1,108,31,153,255,1,108,31,204,255,1,108,31,102,255,1,108,47,51,30,1,0,108,31,15,1,0,108,31,135,1,0,108,31,195,1,0,108,31,225,1,0,108,
31,240,1,0,108,31,120,1,0,108,31,60,1,0,108,47,31,224,2,0,107,47,15,240,2,0,107,47,7,248,2,0,107,47,3,252,2,0,107,47,1,254,2,0,107,47,0,255,2,0,107,47,
...
    codec_t codec
        string name bslz4
        any parameters
            long  1
    long compressedSize 86556
    long uncompressedSize 1048576
    int uniqueId 4300
    time_t dataTimeStamp 2025-12-31 12:35:14.685
        long secondsPastEpoch 1767206114
        int nanoseconds 685011863
    time_t timeStamp 2025-12-31 12:35:14.685
        long secondsPastEpoch 1767206114
        int nanoseconds 685011894
    dimension_t[] dimension
        dimension_t
            int size 1024
            int offset 0
            int fullSize 1024
            int binning 1
            boolean reverse false
        dimension_t
            int size 1024
            int offset 0
            int fullSize 1024
            int binning 1
            boolean reverse false
    epics:nt/NTAttribute:1.0[] attribute
        epics:nt/NTAttribute:1.0
            string name ColorMode
            any value
                long  0
            string[] tags []
            string descriptor Color mode
            alarm_t alarm
                int severity 0
                int status 0
                string message
            time_t timeStamp
                long secondsPastEpoch 0
                int nanoseconds 0
                int userTag 0
            int sourceType 0
            string source Driver
      ...

NDPluginPVA does not have these issues. It correctly displays the compressed images in ImageJ with no error messages.

This is the output of pvget when I switch back to using NDPluginPVA.

(base) [epics@corvette ADSimDetector]$ pvget 13SIM1:Pva1:Image
13SIM1:Pva1:Image epics:nt/NTNDArray:1.0
    union value
        ubyte[]  [0,0,2,155,31,85,1,0,108,31,170,1,0,108,15,255,0,108,31,85,255,0,108,15,0,1,255,239,31,102,1,0,108,31,51,1,0,108,31,153,1,0,108,31,204,1,0,108,15,255,
1,108,31,102,255,1,108,31,51,255,1,108,31,153,255,1,108,47,204,135,1,0,108,31,195,1,0,108,31,225,1,0,108,31,240,1,0,108,31,120,1,0,108,31,60,1,0,108,31,30,1,0,108,31,15,1,0,108,47,7,248,2,0,107,47,3,252,2,0,107,47,1,254,2,0,107,47,0,255,2,0,107,47,128,127,2,0,107,47,192,63,2,0,107,47,224,31,2,0,107,4
...
    codec_t codec
        string name bslz4
        any parameters
            int  5
    long compressedSize 86556
    long uncompressedSize 1048576
    dimension_t[] dimension
        dimension_t
            int size 1024
            int offset 0
            int fullSize 1024
            int binning 1
            boolean reverse false
        dimension_t
            int size 1024
            int offset 0
            int fullSize 1024
            int binning 1
            boolean reverse false
    int uniqueId 270
    time_t dataTimeStamp 2025-12-31 12:47:19.827
        long secondsPastEpoch 1767206839
        int nanoseconds 826854944
        int userTag 0
    epics:nt/NTAttribute:1.0[] attribute
        epics:nt/NTAttribute:1.0
            string name ColorMode
            any value
                int  0
            string descriptor Color mode
            int sourceType 0
            string source Driver
...

The reason for the failure to display the compressed images is that the codec "parameters" are "int 5" for PVA but "long 1" for PVXS.

The codec parameters value should be ScalarType enum as defined here:
https://docs.epics-controls.org/projects/pvdata-cpp/en/latest/doxygen/namespaceepics_1_1pv_data.html#ad70edb4f86fc7bb84d73c5e44f344125

The unsigned 8 bit integer data type, which is the case here, has enum value 5 (pvUByte). That is what PVA is using. PVXS is using 1, which is a different set of enums, where 0= signed byte, 1=unsigned byte, etc.

ntndArrayConverter.cpp defines this mapping from the NDArray datatype to the PVA datatype:

ADCore/ADApp/ntndArrayConverterSrc/ntndArrayConverter.cpp

Line 25 in 6e950ed

static const ScalarType NDDataTypeToScalar[NDFloat64 + 1] = {

That is used to set the codec.parameters in the 4 lines starting here:

ADCore/ADApp/ntndArrayConverterSrc/ntndArrayConverter.cpp

Line 416 in 6e950ed

uncompressedType->putFrom<int32>(NDDataTypeToScalar[src->dataType]);

ntndArrayConverterPvxs is not doing that, it is putting the NDArray datatype into codec.parameters here:

ADCore/ADApp/ntndArrayConverterSrc/ntndArrayConverterPvxs.cpp

Line 345 in a44677e

m_value["codec.parameters"] = (int32_t) src->dataType;

That will not work, because ImageJ is using the Java version of PVA, and uses the same ScalarType enum that the C++ version uses:

https://github.com/areaDetector/ADViewers/blob/f2f811eb47ccb29ecf094d5628d1528fa2b8fa3c/ImageJ/EPICS_areaDetector/EPICS_NTNDA_Viewer.java#L89

PVXS does not support the ScalarType enum. We need to define it in ntndArrayConverterPvxs so we can do the required mapping.

[MarkRivers]

I have fixed the issue with ntndArrayConverterPvxs.cpp not using the correct PVA ScalarType enum in codec.parameters.
#5265fdf

codec.parameters is now 5 for unsigned 8-bit integers, as expected.

However, that still does not allow ImageJ to correctly display compressed arrays. The problem is that ImageJ expects codec.parameters to be an "int", but PVXS sends it as a "long" (i.e. 64-bit integer).