fix sample encoding for export

src/export_edf.jl

@@ -96,18 +96,87 @@ function onda_samples_to_edf_header(samples::AbstractVector{<:Samples};
                           is_contiguous, edf_record_metadata(samples)...)
 end
 
+"""
+    reencode_samples(samples::Samples, sample_type::Type{<:Integer}=Int16)
+
+Re-compute encoding parameters for `samples` so that they can be encoded as
+`sample_type`.  The default `sample_type` is `Int16` which is the target for EDF
+format.
+
+This uses the actual signal extrema, choosing a resolution/offset that maps them
+to `typemin(sample_type), typemax(sample_type`.
+
+Returns an encoded `Samples`, possibly with updated info.  If the current
+encoded values can be represented with `sample_type`, nothing is changed.  If
+they cannot, the `sample_type`, `sample_resolution_in_unit`, and
+`sample_offset_in_unit` fields are changed to reflect the new encoding.
+"""
+function reencode_samples(samples::Samples, sample_type::Type{<:Integer}=Int16)
+    # if we can fit the encoded values in `sample_type` without any changes,
+    # return as-is.
+    #
+    # first, check at the type level since this is cheap and doesn't require
+    # re-encoding possibly decoded values
+    current_type = Onda.sample_type(samples.info)
+    typemin(current_type) >= typemin(sample_type) &&
+        typemax(current_type) <= typemax(sample_type) &&
+        return encode(samples)
+
+    # next, check whether the encoded values are <: Integers that lie within the
+    # range representable by `sample_type` and can be converted directly.
+    if Onda.sample_type(samples.info) <: Integer
+        smin, smax = extrema(samples.data)
+        if !samples.encoded
+            smin, smax = Onda.encode_sample.(Onda.sample_type(samples.info),
+                                             samples.info.sample_resolution_in_unit,
+                                             samples.info.sample_offset_in_unit,
+                                             (smin, smax))
+        end
+        if smin >= typemin(sample_type) && smax <= typemax(sample_type)
+            # XXX: we're being a bit clever here in order to not allocate a
+            # whole new sample array, plugging in the new sample_type, re-using
+            # the old encodoed samples data, and skipping validation.  this is
+            # okay in _this specific context_ since we know we're actually
+            # converting everything to Int16 in the actual export.
+            samples = encode(samples)
+            new_info = SamplesInfoV2(Tables.rowmerge(samples.info; sample_type))
+            return Samples(samples.data, new_info, true; validate=false)
+        end
+    end
+
+    # at this point, we know the currently _encoded_ values cannot be
+    # represented losslessly as Int16, so we need to re-encode.  We'll pick new
+    # encoding parameters based on the actual signal values, in order to
+    # maximize the dynamic range of Int16 encoding.
+    samples = decode(samples)
+    smin, smax = extrema(samples.data)
+
+    emin, emax = typemin(sample_type), typemax(sample_type)
+
+    # re-use the import encoding calculator here:
+    # need to convert all the min/max to floats due to possible overflow
+    mock_header = (; digital_minimum=Float64(emin), digital_maximum=Float64(emax),
+                   physical_minimum=Float64(smin), physical_maximum=Float64(smax),
+                   samples_per_record=0) # not using this
+
+    donor_info = edf_signal_encoding(mock_header, 1)
+    sample_resolution_in_unit = donor_info.sample_resolution_in_unit
+    sample_offset_in_unit = donor_info.sample_offset_in_unit
+
+    new_info = Tables.rowmerge(samples.info;
+                               sample_resolution_in_unit,
+                               sample_offset_in_unit,
+                               sample_type)
+
+    new_samples = Samples(samples.data, SamplesInfoV2(new_info), samples.encoded)
+    return encode(new_samples)
+end
+
 function onda_samples_to_edf_signals(onda_samples::AbstractVector{<:Samples}, seconds_per_record::Float64)
     edf_signals = Union{EDF.AnnotationsSignal,EDF.Signal{Int16}}[]
     for samples in onda_samples
         # encode samples, rescaling if necessary
-        if sizeof(sample_type(samples.info)) > sizeof(Int16)
-            decoded_samples = Onda.decode(samples)
-            scaled_resolution = samples.info.sample_resolution_in_unit * (sizeof(sample_type(samples.info)) / sizeof(Int16))
-            encode_info = SamplesInfoV2(Tables.rowmerge(samples.info; sample_type=Int16, sample_resolution_in_unit=scaled_resolution))
-            samples = encode(Onda.Samples(decoded_samples.data, encode_info, false))
-        else
-            samples = Onda.encode(samples)
-        end
+        samples = reencode_samples(samples, Int16)
         signal_name = samples.info.sensor_type
         extrema = SignalExtrema(samples)
         for channel_name in samples.info.channels
@@ -118,7 +187,9 @@ function onda_samples_to_edf_signals(onda_samples::AbstractVector{<:Samples}, se
                                                  extrema.physical_min, extrema.physical_max,
                                                  extrema.digital_min, extrema.digital_max,
                                                  "", sample_count)
-            sample_data = vec(samples[channel_name, :].data)
+            # manually convert here in case we have input samples whose encoded
+            # values are convertible losslessly to Int16:
+            sample_data = Int16.(vec(samples[channel_name, :].data))
             padding = Iterators.repeated(zero(Int16), (sample_count - (length(sample_data) % sample_count)) % sample_count)
             edf_signal_samples = append!(sample_data, padding)
             push!(edf_signals, EDF.Signal(edf_signal_header, edf_signal_samples))
@@ -150,6 +221,18 @@ input `Onda.Samples`.
 The ordering of `EDF.Signal`s in the output will match the order of the input
 collection of `Samples` (and within each channel grouping, the order of the
 samples' channels).
+
+!!! note
+
+    EDF signals are encoded as Int16, while Onda allows a range of different
+    sample types, some of which provide considerably more resolution than Int16.
+    During export, re-encoding may be necessary if the encoded Onda samples
+    cannot be represented directly as Int16 values.  In this case, new encoding
+    (resolution and offset) will be chosen based on the minimum and maximum
+    values actually present in each _signal_ in the input Onda Samples.  Thus,
+    it may not always be possible to losslessly round trip Onda-formatted
+    datasets to EDF and back.
+
 """
 function onda_to_edf(samples::AbstractVector{<:Samples}, annotations=[]; kwargs...)
     edf_header = onda_samples_to_edf_header(samples; kwargs...)

test/export.jl

@@ -14,7 +14,7 @@
     exported_edf = onda_to_edf(samples_to_export, annotations)
     @test exported_edf.header.record_count == 200
     offset = 0
-    for signal_name in signal_names
+    @testset "export $signal_name" for signal_name in signal_names
         samples = only(filter(s -> s.info.sensor_type == signal_name, onda_samples))
         channel_names = samples.info.channels
         edf_indices = (1:length(channel_names)) .+ offset
@@ -97,19 +97,18 @@
         # new UUID for each annotation created during import
         @test all(getproperty.(nt.annotations, :id) .!= getproperty.(ann_sorted, :id))
 
-        for (samples_orig, signal_round_tripped) in zip(onda_samples, nt.signals)
+        @testset "$(samples_orig.info.sensor_type)" for (samples_orig, signal_round_tripped) in zip(onda_samples, nt.signals)
             info_orig = samples_orig.info
             info_round_tripped = SamplesInfoV2(signal_round_tripped)
-            for p in setdiff(propertynames(info_orig),
-                             (:edf_channels, :sample_type, :sample_resolution_in_unit))
-                @test getproperty(info_orig, p) == getproperty(info_round_tripped, p)
-            end
-            if info_orig.sample_type == "int32"
-                resolution_orig = info_orig.sample_resolution_in_unit * 2
-            else
-                resolution_orig = info_orig.sample_resolution_in_unit
+
+            # anything else, the encoding parameters may change on export
+            if info_orig.sample_type == "int16"
+                @test info_orig == info_round_tripped
             end
-            @test resolution_orig ≈ info_round_tripped.sample_resolution_in_unit
+
+            samples_rt = Onda.load(signal_round_tripped)
+            @test all(isapprox.(decode(samples_orig).data, decode(samples_rt).data;
+                                atol=info_orig.sample_resolution_in_unit))
         end
 
         # don't import annotations
@@ -122,4 +121,110 @@
         @test_logs (:warn, r"No annotations found in") store_edf_as_onda(exported_edf2, mktempdir(), uuid; import_annotations=true)
     end
 
+    @testset "re-encoding" begin
+        _flatten_union(T::Union) = vcat(T.a, _flatten_union(T.b))
+        _flatten_union(T::Type) = T
+
+        onda_types = _flatten_union(Onda.LPCM_SAMPLE_TYPE_UNION)
+
+        onda_ints = filter(x -> x <: Integer, onda_types)
+        onda_floats = filter(x -> x <: AbstractFloat, onda_types)
+        @test issetequal(union(onda_ints, onda_floats), onda_types)
+
+        # test that we can encode ≈ the full range of values expressible in each
+        # possible Onda sample type.
+        @testset "encoding $T" for T in onda_types
+            info = SamplesInfoV2(; sensor_type="x",
+                                 channels=["x"],
+                                 sample_unit="microvolt",
+                                 sample_resolution_in_unit=2,
+                                 sample_offset_in_unit=1,
+                                 sample_type=T,
+                                 sample_rate=1)
+
+            if T <: AbstractFloat
+                min = nextfloat(typemin(T))
+                max = prevfloat(typemax(T))
+                data = range(min, max; length=9)
+            else
+                min = typemin(T)
+                max = typemax(T)
+                step = max ÷ T(8) - min ÷ T(8)
+                data = range(min, max; step)
+            end
+
+            data = reshape(data, 1, :)
+            samples = Samples(data, info, true)
+
+            # for  r e a s o n s  we need to be a bit careful with just how large
+            # the values are that we're trying to use; EDF.jl (and maybe EDF
+            # generally, unclear) can't handle physical min/max more than like
+            # 1e8 (actually for EDF.jl it's 99999995 because Float32 precision).
+            # so, we try to do typemax/min of the encoded type, and if that
+            # leads to physical min/max that are too big, we clamp and
+            # re-encode.
+            if !all(<(1e10) ∘ abs ∘ float, decode(samples).data)
+                @info "clamped decoded $(T) samples to ±1e10"
+                min_d, max_d = -1e10, 1e10
+                data_d = reshape(range(min_d, max_d; length=9), 1, :)
+                samples = Onda.encode(Samples(data_d, info, false))
+            end
+
+            signal = only(OndaEDF.onda_samples_to_edf_signals([samples], 1.0))
+
+            @test vec(decode(samples).data) ≈ EDF.decode(signal)
+        end
+
+        @testset "skip reencoding" begin
+            info = SamplesInfoV2(; sensor_type="x",
+                                 channels=["x"],
+                                 sample_unit="microvolt",
+                                 sample_resolution_in_unit=2,
+                                 sample_offset_in_unit=1,
+                                 sample_type=Int32,
+                                 sample_rate=1)
+
+            data = Int32[typemin(Int16) typemax(Int16)]
+
+            samples = Samples(data, info, true)
+            # data is re-used if already encoded
+            @test OndaEDF.reencode_samples(samples, Int16).data === samples.data
+            signal = only(OndaEDF.onda_samples_to_edf_signals([samples], 1.0))
+            @test EDF.decode(signal) == vec(decode(samples).data)
+
+            # make sure it works with decoded too
+            signal2 = only(OndaEDF.onda_samples_to_edf_signals([Onda.decode(samples)], 1.0))
+            @test EDF.decode(signal2) == vec(decode(samples).data)
+            # to confirm quantization settings are the same
+            @test signal.header == signal2.header
+
+            # bump just outside the range representable as Int16
+            samples.data .+= Int32[-1 1]
+            new_samples = OndaEDF.reencode_samples(samples, Int16)
+            @test new_samples != samples
+            @test decode(new_samples).data == decode(samples).data
+
+            signal = only(OndaEDF.onda_samples_to_edf_signals([samples], 1.0))
+            @test EDF.decode(signal) == vec(decode(samples).data)
+            # to confirm quantization settings are changed
+            @test signal.header != signal2.header
+
+
+            uinfo = SamplesInfoV2(Tables.rowmerge(info; sample_type="uint64"))
+            data = UInt64[0 typemax(Int16)]
+            samples = Samples(data, uinfo, true)
+            @test OndaEDF.reencode_samples(samples, Int16).data === samples.data
+            signal = only(OndaEDF.onda_samples_to_edf_signals([samples], 1.0))
+            @test EDF.decode(signal) == vec(decode(samples).data)
+
+            samples.data .+= UInt64[0 1]
+            new_samples = OndaEDF.reencode_samples(samples, Int16)
+            @test new_samples != samples
+            @test decode(new_samples).data == decode(samples).data
+
+            signal = only(OndaEDF.onda_samples_to_edf_signals([samples], 1.0))
+            @test EDF.decode(signal) == vec(decode(samples).data)
+        end
+    end
+
 end