m3_lightmeter/lib/utils/ev_from_bytes.dart

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import 'dart:math' as math;
import 'package:exif/exif.dart';
import 'package:flutter/foundation.dart';
import 'package:m3_lightmeter_resources/m3_lightmeter_resources.dart';
Future<double> evFromImage(Uint8List bytes) async {
final tags = await readExifFromBytes(bytes);
final iso = double.tryParse("${tags["EXIF ISOSpeedRatings"]}");
final apertureValueRatio = (tags["EXIF FNumber"]?.values as IfdRatios?)?.ratios.first;
final speedValueRatio = (tags["EXIF ExposureTime"]?.values as IfdRatios?)?.ratios.first;
if (iso == null || apertureValueRatio == null || speedValueRatio == null) {
throw ArgumentError(
'Error parsing EXIF: ${tags.keys.join(', ')}',
[
if (iso == null) 'EXIF ISOSpeedRatings',
if (apertureValueRatio == null) 'EXIF FNumber',
if (speedValueRatio == null) 'EXIF ExposureTime',
].join(', '),
);
}
final aperture = apertureValueRatio.numerator / apertureValueRatio.denominator;
final speed = speedValueRatio.numerator / speedValueRatio.denominator;
return log2(math.pow(aperture, 2)) - log2(speed) - log2(iso / 100);
}