Update docs

Author: thisisaaronland

README.md

@@ -8,14 +8,16 @@ The blog post [Updating EXIF metadata in JavaScript (and WebAssembly)](https://m
 
 ## Important
 
-As of this writing the majority of EXIF tags are _not_ supported. Currently only EXIF tags of types `ASCII` and `BYTE` are supported. This is not ideal but I am still trying to get familiar with the requirements of the `go-exif` package. Contributions and patches for the other remaining EXIF tag types is welcomed.
+As of this writing the majority of EXIF tags are _not_ supported. Currently only EXIF tags of with the following EXIF types are supported: `ASCII`, `BYTE`, `RATIONAL` and `SRATIONAL` are supported. This is not ideal but I am still trying to get familiar with the requirements of the `go-exif` package. Contributions and patches for the other remaining EXIF tag types is welcomed.
 
 ## Documentation
 
 [![Go Reference](https://pkg.go.dev/badge/github.com/sfomuseum/go-exif-update.svg)](https://pkg.go.dev/github.com/sfomuseum/go-exif-update)
 
 ### Example
 
+_Error handling removed for the sake of brevity._
+
 ```
 package main
 
@@ -41,10 +43,36 @@ func main() {
 		update.UpdateExif(fh, os.Stdout, exif_props)
 	}
 }
+```
+
+The properties passed to the [UpdateExif](https://pkg.go.dev/github.com/sfomuseum/go-exif-update#UpdateExif) method are assumed to be suitably typed to be used as input for the [exif.SetStandardWithName](https://pkg.go.dev/github.com/dsoprea/go-exif/v3#IfdBuilder.SetStandardWithName) method. For anything other than simple strings this can become a fairly involved process. I am still trying the understand the `go-exif` documentation and requirements so any guidance I have to offer remains limited.
+
+This package also provides a convenience [PrepareAndUpdateExif](https://pkg.go.dev/github.com/sfomuseum/go-exif-update#PrepareUpdateExif) method which attempts to translate EXIF property values in to their corresponding `go-exif` type before invoking the `UpdateExif` method. For example:
 
 ```
+	exif_props := map[string]interface{}{
+		"FNumber": "11/1",	// FNumber is stored as a `RATIONAL` value rather than as a string (or `ASCI`)
+	}
+	
+	for _, path := range paths {
 
-_Error handling removed for the sake of brevity._
+		fh, _ := os.Open(path)
+		defer fh.Close()
+
+		update.PrepareAndUpdateExif(fh, os.Stdout, exif_props)
+	}
+```
+
+### Non-standard tags
+
+The `PrepareAndUpdateExif` method also supports a limited set of custom non-standard tags. These are provided to simplify the process of assigning multiple or complex EXIF tags.
+
+The list of currently supported non-standard tags is:
+
+| Name | Value | Description | Notes |
+| --- | --- | --- | --- |
+| `X-Latitude` | float64 | Assign a decimal latitude value in to its corresponding `GPSLatitude` and `GPSLatitudeRef` properties. | |
+| `X-Longitude` | float64 | Assign a decimal longitude value in to its corresponding `GPSLongitude` and `GPSLongitudeRef` properties. | |
 
 ## Tools
 
@@ -86,6 +114,8 @@ Copyright true
 ImageWidth false
 ```
 
+_As of this writing non-standard tags, described above, are not considered when processing tags._
+
 ### tags-supported
 
 Command-line tool that prints a list of EXIF tag names, sorted alphabetically, that are supported by the sfomuseum/go-exif-update package.
@@ -98,6 +128,8 @@ Usage:
 	./bin/tags-supported
 ```
 
+_As of this writing non-standard tags, described above, are not considered when listing supported tags._
+
 ### update-exif
 
 Command-line tool for updating the EXIF properties in one or more JPEG images.
@@ -130,6 +162,26 @@ Exif.Image.Artist                            Ascii       4  Bob
 Exif.Image.Copyright                         Ascii       6  Alice
 ```
 
+This tool uses the `PrepareAndUpdateExif` method and supports non-standard tags, both described above. For example:
+
+```
+$> ./bin/update-exif \
+	-property X-Latitude=37.61799 \
+	-property X-Longitude=-122.384864 \
+	-property Artist=Walrus \
+	fixtures/walrus.jpg \
+
+> walrus-exif.jpg
+
+$> exiv2 -pa walrus-exif.jpg 
+Exif.Image.GPSTag                            Long        1  45
+Exif.GPSInfo.GPSLongitude                    Rational    3  122deg 23' 5"
+Exif.GPSInfo.GPSLongitudeRef                 Ascii       2  West
+Exif.GPSInfo.GPSLatitude                     Rational    3  37deg 37' 4"
+Exif.GPSInfo.GPSLatitudeRef                  Ascii       2  North
+Exif.Image.Artist                            Ascii       7  Walrus
+```
+
 ### update-exif-wasm-demo
 
 HTTP server for demonstrating the use of the update_exif WebAssembly binary.
@@ -197,44 +249,102 @@ An abbreviated version of the code to use the `update_exif.wasm` binary in JavaS
 
 For a complete example consult the [www/javascript/index.js](www/javascript/index.js) file.
 
+The WASM binary included with tool uses the `PrepareAndUpdateExif` method and supports non-standard tags, both described above.
+
 ## Supported tags
 
 The following EXIF tags are supported by this package. This list was generated by the `tags-supported` tool.
 
 ```
+AnalogBalance
+AntiAliasStrength
+ApertureValue
+ApertureValue
 Artist
+AsShotPreProfileMatrix
 AsShotProfileName
+AsShotWhiteXY
+BaselineExposure
+BaselineNoise
+BaselineSharpness
+BatteryLevel
+BestQualityScale
+BlackLevel
+BlackLevelDeltaH
+BlackLevelDeltaV
 BodySerialNumber
+BrightnessValue
+BrightnessValue
 CFAPattern
 CFAPlaneColor
+CameraCalibration1
+CameraCalibration2
 CameraCalibrationSignature
 CameraOwnerName
 CameraSerialNumber
+ChromaBlurRadius
 ClipPath
+ColorMatrix1
+ColorMatrix2
+CompressedBitsPerPixel
+CompressedBitsPerPixel
 Copyright
+CurrentPreProfileMatrix
 DNGBackwardVersion
 DNGPrivateData
 DNGVersion
 DateTime
 DateTimeDigitized
 DateTimeOriginal
 DateTimeOriginal
+DefaultScale
+DigitalZoomRatio
 DocumentName
 DotRange
+ExposureBiasValue
+ExposureBiasValue
+ExposureIndex
+ExposureIndex
+ExposureTime
+ExposureTime
+FNumber
+FNumber
+FlashEnergy
+FlashEnergy
+FocalLength
+FocalLength
+FocalPlaneXResolution
+FocalPlaneXResolution
+FocalPlaneYResolution
+FocalPlaneYResolution
+ForwardMatrix1
+ForwardMatrix2
+GPSAltitude
 GPSAltitudeRef
+GPSDOP
 GPSDateStamp
+GPSDestBearing
 GPSDestBearingRef
+GPSDestDistance
 GPSDestDistanceRef
+GPSDestLatitude
 GPSDestLatitudeRef
+GPSDestLongitude
 GPSDestLongitudeRef
+GPSImgDirection
 GPSImgDirectionRef
+GPSLatitude
 GPSLatitudeRef
+GPSLongitude
 GPSLongitudeRef
 GPSMapDatum
 GPSMeasureMode
 GPSSatellites
+GPSSpeed
 GPSSpeedRef
 GPSStatus
+GPSTimeStamp
+GPSTrack
 GPSTrackRef
 GPSVersionID
 HostComputer
@@ -245,19 +355,26 @@ ImageResources
 ImageUniqueID
 InkNames
 InteroperabilityIndex
+LensInfo
 LensMake
 LensModel
 LensSerialNumber
+LensSpecification
+LinearResponseLimit
 LocalizedCameraModel
 Make
+MaxApertureValue
+MaxApertureValue
 Model
 NoiseProfile
+NoiseReductionApplied
 OriginalRawFileName
 PreviewApplicationName
 PreviewApplicationVersion
 PreviewDateTime
 PreviewSettingsDigest
 PreviewSettingsName
+PrimaryChromaticities
 ProcessingSoftware
 ProfileCalibrationSignature
 ProfileCopyright
@@ -267,27 +384,39 @@ ProfileLookTableData
 ProfileName
 ProfileToneCurve
 RawDataUniqueID
+ReductionMatrix1
+ReductionMatrix2
+ReferenceBlackWhite
 RelatedImageFileFormat
 RelatedSoundFile
 SecurityClassification
+ShadowScale
+ShutterSpeedValue
+ShutterSpeedValue
 Software
 SpectralSensitivity
 SpectralSensitivity
 SubSecTime
 SubSecTimeDigitized
 SubSecTimeOriginal
+SubjectDistance
+SubjectDistance
 TIFFEPStandardID
 TargetPrinter
 TimeZoneOffset
 UniqueCameraModel
+WhitePoint
 XClipPathUnits
 XMLPacket
 XPAuthor
 XPComment
 XPKeywords
 XPSubject
 XPTitle
+XResolution
+YCbCrCoefficients
 YClipPathUnits
+YResolution
 ```
 
 ## See also

cmd/tags-supported-wasm/main.go

@@ -20,7 +20,7 @@ func main() {
 			log.Printf("Failed to derive supported tags, %v", err)
 			return nil
 		}
-		
+
 		sort.Strings(tags_supported)
 
 		x_tags := []string{
@@ -31,7 +31,7 @@ func main() {
 		for _, t := range x_tags {
 			tags_supported = append(tags_supported, t)
 		}
-		
+
 		enc_supported, err := json.Marshal(tags_supported)
 
 		if err != nil {

cmd/update-exif/main.go

@@ -16,9 +16,6 @@ func main() {
 	var properties multi.KeyValueString
 	flag.Var(&properties, "property", "One or more {TAG}={VALUE} EXIF properties. {TAG} must be a recognized EXIF tag.")
 
-	lat := flag.Float64("latitude", 0.0, "")
-	lon := flag.Float64("longitude", 0.0, "")
-
 	flag.Usage = func() {
 		fmt.Fprintf(os.Stderr, "Command-line tool for updating the EXIF properties in one or more JPEG images. Images are not updated in place but written to STDOUT.\n\n")
 		fmt.Fprintf(os.Stderr, "Usage:\n\t%s [options] image(N) image(N) image(N)\n\n", os.Args[0])
@@ -52,15 +49,6 @@ func main() {
 		exif_props[k] = v
 	}
 
-	if *lat != 0.0 && *lon != 0.0 {
-
-		err := update.AppendGPSPropertiesWithLatitudeAndLongitude(exif_props, *lat, *lon)
-
-		if err != nil {
-			log.Fatalf("Failed to append latitude and longitude properties, %v", err)
-		}
-	}
-
 	for _, path := range paths {
 
 		fh, err := os.Open(path)

update.go

@@ -179,6 +179,24 @@ func UpdateExif(r io.Reader, wr io.Writer, exif_props map[string]interface{}) er
 	return sl.Write(wr)
 }
 
+// Return the *exifcommon.IfdIdentity and *exif.IndexedTag instances associated
+// with a given EXIF string tag name.
+func GetIndexedTagFromName(k string) (*exifcommon.IfdIdentity, *exif.IndexedTag, error) {
+
+	for _, id := range tag_paths {
+
+		t, err := ti.GetWithName(id, k)
+
+		if err != nil {
+			continue
+		}
+
+		return id, t, nil
+	}
+
+	return nil, nil, fmt.Errorf("Unrecognized tag, %s", k)
+}
+
 // Cribbed from https://github.com/dsoprea/go-exif/issues/11
 
 func setExifTag(rootIB *exif.IfdBuilder, ifdPath string, tagName string, tagValue interface{}) error {
@@ -199,21 +217,3 @@ func setExifTag(rootIB *exif.IfdBuilder, ifdPath string, tagName string, tagValu
 
 	return nil
 }
-
-// Return the *exifcommon.IfdIdentity and *exif.IndexedTag instances associated
-// with a given EXIF string tag name.
-func GetIndexedTagFromName(k string) (*exifcommon.IfdIdentity, *exif.IndexedTag, error) {
-
-	for _, id := range tag_paths {
-
-		t, err := ti.GetWithName(id, k)
-
-		if err != nil {
-			continue
-		}
-
-		return id, t, nil
-	}
-
-	return nil, nil, fmt.Errorf("Unrecognized tag, %s", k)
-}