Add tags ScaleFactorTo35mmEquivalent, FieldOfView

First composite values. Only the simple variants of these values where we have FocalLengthIn35mmFilm that can be used for the calculation.

#488 #491

Author: mattiasw

dist/exif-reader.js

@@ -0,0 +1,75 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
+
+export default {
+    get,
+};
+
+function get(tags, expanded) {
+    const compositeTags = {};
+    let hasCompositeTags = false;
+
+    const focalLength = getTagValue(tags, 'FocalLength', expanded);
+    const focalLengthIn35mmFilm = getTagValue(tags, 'FocalLengthIn35mmFilm', expanded);
+
+    const scaleFactorTo35mmEquivalent = getScaleFactorTo35mmEquivalent(focalLength, focalLengthIn35mmFilm);
+    if (scaleFactorTo35mmEquivalent) {
+        compositeTags.ScaleFactorTo35mmEquivalent = scaleFactorTo35mmEquivalent;
+        hasCompositeTags = true;
+    }
+
+    const fieldOfView = getFieldOfView(focalLengthIn35mmFilm);
+    if (fieldOfView) {
+        compositeTags.FieldOfView = fieldOfView;
+        hasCompositeTags = true;
+    }
+
+    if (hasCompositeTags) {
+        return compositeTags;
+    }
+
+    return undefined;
+}
+
+function getTagValue(tags, tagName, expanded) {
+    if (expanded && tags.exif && tags.exif[tagName]) {
+        return tags.exif[tagName].value;
+    }
+    if (!expanded && tags[tagName]) {
+        return tags[tagName].value;
+    }
+    return undefined;
+}
+
+function getScaleFactorTo35mmEquivalent(focalLength, focalLengthIn35mmFilm) {
+    if (focalLength && focalLengthIn35mmFilm) {
+        try {
+            const value = focalLengthIn35mmFilm / (focalLength[0] / focalLength[1]);
+            return {
+                value,
+                description: value.toFixed(1),
+            };
+        } catch (error) {
+            // Ignore.
+        }
+    }
+    return undefined;
+}
+
+function getFieldOfView(focalLengthIn35mmFilm) {
+    const FULL_FRAME_SENSOR_WIDTH_MM = 36;
+
+    if (focalLengthIn35mmFilm) {
+        try {
+            const value = 2 * Math.atan(FULL_FRAME_SENSOR_WIDTH_MM / (2 * focalLengthIn35mmFilm)) * (180 / Math.PI);
+            return {
+                value,
+                description: value.toFixed(1) + ' deg',
+            };
+        } catch (error) {
+            // Ignore.
+        }
+    }
+    return undefined;
+}

dist/exif-reader.js.map

@@ -29,6 +29,7 @@ import PngTags from './png-tags.js';
 import Vp8xTags from './vp8x-tags.js';
 import GifFileTags from './gif-file-tags.js';
 import Thumbnail from './thumbnail.js';
+import Composite from './composite.js';
 import exifErrors from './errors.js';
 
 export default {
@@ -419,6 +420,15 @@ export function loadView(
         }
     }
 
+    const composite = Composite.get(tags, expanded);
+    if (composite) {
+        if (expanded) {
+            tags.composite = composite;
+        } else {
+            tags = objectAssign({}, tags, composite);
+        }
+    }
+
     const thumbnail = (Constants.USE_JPEG || Constants.USE_WEBP)
         && Constants.USE_EXIF
         && Constants.USE_THUMBNAIL

src/composite.js

@@ -295,12 +295,12 @@ export default {
         }
     },
     0xa405: {
-        'name': 'FocalLengthIn35mmFilm',
+        'name': 'FocalLengthIn35mmFilm', // Sometimes called FocalLengthIn35mmFormat.
         'description': (value) => {
             if (value === 0) {
                 return 'Unknown';
             }
-            return value;
+            return value + ' mm';
         }
     },
     0xa406: {

src/exif-reader.js

@@ -0,0 +1,35 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
+
+import {expect} from 'chai';
+import Composite from '../../src/composite';
+
+describe('composite', () => {
+    it('should return undefined when there is nothing to calculate', () => {
+        expect(Composite.get({}, false)).to.be.undefined;
+        expect(Composite.get({exif: {}}, true)).to.be.undefined;
+    });
+
+    it('should calculate ScaleFactorTo35mmEquivalent', () => {
+        const tags = {FocalLength: {value: [4500, 1000]}, FocalLengthIn35mmFilm: {value: 24}};
+        const expected = {
+            value: 5.333333333333333,
+            description: '5.3'
+        };
+
+        expect(Composite.get(tags, false).ScaleFactorTo35mmEquivalent).to.deep.equal(expected);
+        expect(Composite.get({exif: tags}, true).ScaleFactorTo35mmEquivalent).to.deep.equal(expected);
+    });
+
+    it('should calculate FieldOfView', () => {
+        const tags = {FocalLengthIn35mmFilm: {value: 24}};
+        const expected = {
+            value: 73.73979529168804,
+            description: '73.7 deg'
+        };
+
+        expect(Composite.get(tags, false).FieldOfView).to.deep.equal(expected);
+        expect(Composite.get({exif: tags}, true).FieldOfView).to.deep.equal(expected);
+    });
+});

src/tag-names-exif-ifd.js

@@ -32,6 +32,7 @@ describe('exif-reader', function () {
         ExifReaderRewireAPI.__ResetDependency__('Vp8xTags');
         ExifReaderRewireAPI.__ResetDependency__('GifFileTags');
         ExifReaderRewireAPI.__ResetDependency__('Thumbnail');
+        ExifReaderRewireAPI.__ResetDependency__('Composite');
     });
 
     it('should throw an error if the passed buffer is non-compliant', () => {
@@ -598,6 +599,19 @@ describe('exif-reader', function () {
         expect(ExifReader.loadView({}, {expanded: true})).to.deep.equal({...myTags, file: {FileType: {value: 'webp', description: 'WebP'}}});
     });
 
+    it('should calculate composite values', () => {
+        const myTags = {MyExifTag: 42};
+        const compositeTags = {MyCompositeTag: 4711};
+        rewireForLoadView({tiffHeaderOffset: OFFSET_TEST_VALUE}, 'Tags', myTags);
+        ExifReaderRewireAPI.__Rewire__('Composite', {
+            get() {
+                return compositeTags;
+            }
+        });
+
+        expect(ExifReader.loadView()).to.deep.equal({...myTags, ...compositeTags});
+    });
+
     describe('gps group', () => {
         it('should not create a "gps" group if there are no GPS values', () => {
             const myTags = {MyExifTag: 43};

test/unit/composite-spec.js

@@ -424,7 +424,7 @@ describe('tag-names-exif-ifd', () => {
     it('should report correct name and description for FocalLengthIn35mmFilm', () => {
         expect(TagNamesExifIfd[0xa405].name).to.equal('FocalLengthIn35mmFilm');
         expect(TagNamesExifIfd[0xa405].description(0)).to.equal('Unknown');
-        expect(TagNamesExifIfd[0xa405].description(4711)).to.equal(4711);
+        expect(TagNamesExifIfd[0xa405].description(4711)).to.equal('4711 mm');
     });
 
     it('should report correct name and description for SceneCaptureType', () => {