NDPluginPvxs does not work with ImageJ with compressed arrays

[MarkRivers]

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

31-Dec-2025 12:30:51.982: color mode is not an int
31-Dec-2025 12:30:51.982: handleEvents caught exception java.lang.NullPointerException

and the images do not update.

When sending uncompressed arrays the images do update, but this error message is still present for each image received:

31-Dec-2025 12:30:53.080: color mode is not an int
31-Dec-2025 12:30:53.180: color mode is not an int
31-Dec-2025 12:30:53.282: color mode is not an int

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
        epics:nt/NTAttribute:1.0
            string name Int8
            any value
                long  -8
            string[] tags []
            string descriptor Int8 attribute
            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 3
            string source myAttrFunct1
        epics:nt/NTAttribute:1.0
            string name UInt8
            any value
                ulong  8
            string[] tags []
            string descriptor UInt8 attribute
            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 3
            string source myAttrFunct1
        epics:nt/NTAttribute:1.0
            string name Int16
            any value
                long  -16
            string[] tags []
            string descriptor Int16 attribute
            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 3
            string source myAttrFunct1
        epics:nt/NTAttribute:1.0
            string name UInt16
            any value
                ulong  16
            string[] tags []
            string descriptor UInt16 attribute
            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 3
            string source myAttrFunct1
        epics:nt/NTAttribute:1.0
            string name Int32
            any value
                long  -32
            string[] tags []
            string descriptor Int32 attribute
            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 3
            string source myAttrFunct1
        epics:nt/NTAttribute:1.0
            string name UInt32
            any value
                ulong  32
            string[] tags []
            string descriptor UInt32 attribute
            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 3
            string source myAttrFunct1
        epics:nt/NTAttribute:1.0
            string name Int64
            any value
                long  -64
            string[] tags []
            string descriptor Int64 attribute
            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 3
            string source myAttrFunct1
        epics:nt/NTAttribute:1.0
            string name UInt64
            any value
                ulong  64
            string[] tags []
            string descriptor UInt64 attribute
            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 3
            string source myAttrFunct1
        epics:nt/NTAttribute:1.0
            string name Float32
            any value
                double  32
            string[] tags []
            string descriptor Float32 attribute
            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 3
            string source myAttrFunct1
        epics:nt/NTAttribute:1.0
            string name Float64
            any value
                double  64
            string[] tags []
            string descriptor Float64 attribute
            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 3
            string source myAttrFunct1

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
        epics:nt/NTAttribute:1.0
            string name Int8
            any value
                byte  -8
            string descriptor Int8 attribute
            int sourceType 3
            string source myAttrFunct1
        epics:nt/NTAttribute:1.0
            string name UInt8
            any value
                ubyte  8
            string descriptor UInt8 attribute
            int sourceType 3
            string source myAttrFunct1
        epics:nt/NTAttribute:1.0
            string name Int16
            any value
                short  -16
            string descriptor Int16 attribute
            int sourceType 3
            string source myAttrFunct1
        epics:nt/NTAttribute:1.0
            string name UInt16
            any value
                ushort  16
            string descriptor UInt16 attribute
            int sourceType 3
            string source myAttrFunct1
        epics:nt/NTAttribute:1.0
            string name Int32
            any value
                int  -32
            string descriptor Int32 attribute
            int sourceType 3
            string source myAttrFunct1
        epics:nt/NTAttribute:1.0
            string name UInt32
            any value
                uint  32
            string descriptor UInt32 attribute
            int sourceType 3
            string source myAttrFunct1
        epics:nt/NTAttribute:1.0
            string name Int64
            any value
                long  -64
            string descriptor Int64 attribute
            int sourceType 3
            string source myAttrFunct1
        epics:nt/NTAttribute:1.0
            string name UInt64
            any value
                ulong  64
            string descriptor UInt64 attribute
            int sourceType 3
            string source myAttrFunct1
        epics:nt/NTAttribute:1.0
            string name Float32
            any value
                float  32
            string descriptor Float32 attribute
            int sourceType 3
            string source myAttrFunct1
        epics:nt/NTAttribute:1.0
            string name Float64
            any value
                double  64
            string descriptor Float64 attribute
            int sourceType 3
            string source myAttrFunct1
    string descriptor
    alarm_t alarm
        int severity 0
        int status 0
        string message
    time_t timeStamp 2025-12-31 12:47:19.827
        long secondsPastEpoch 1767206839
        int nanoseconds 826855001
        int userTag 0
    display_t display
        double limitLow 0
        double limitHigh 0
        string description
        string format
        string units

This shows the reason for the ColorMode error: PVA says the value is "int 0" but PVXS says it is "long 0".

Most of the attributes have the wrong datatype. For example the attribute named UInt8 has the value "ubyte 8" with PVA but "ulong 8" with PVXS.

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

[MarkRivers]

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

I believe 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.

[MarkRivers]

The problem with the compression is indeed the datatype parameter stored in codec.parameters.

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

ADCore/ADApp/ntndArrayConverterSrc/ntndArrayConverter.cpp

Line 25 in a44677e

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 a44677e

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/a9ce8e27adf27a2087a70ae6d22b2b7ea4a00894/ImageJ/EPICS_areaDetector/NTNDCodec.java#L89

PVXS does not appear to support the ScalarType enum. I guess this means we need to define it in ntndArrayConverterPvxs so we can do the required mapping?

It also appears to me that PVXS does not support storing fields like Int8, UInt8, etc. It seems to only support these types:

//! selector for union FieldStorage::store
enum struct StoreType : uint8_t {
    Null,     //!< no associate storage
    Bool,     //!< bool
    UInteger, //!< uint64_t
    Integer,  //!< int64_t
    Real,     //!< double
    String,   //!< std::string
    Compound, //!< Value
    Array,    //!< shared_array<const void>
};

That would explain why the datatypes of the attributes in the example above are mostly "long" rather than the types that are used with PVA.

Is this correct? If so, then it breaks existing clients which are expecting a richer set of datatypes.

[MarkRivers]

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

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).

I had expected that PVXS was just a different implementation of pvAccess, and that it would use the same network protocol as PVA. This is not the case. Clients like ImageJ need to be rewritten to work with PVXS rather than PVA.

Note that ImageJ also cannot display color images with PVXS because ImageJ expects the ColorMode attribute to be an "int", but PXVS sends it as a "long".