exifdescriptor.java

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        // '4' multi-spot, '5' multi-segment, '6' partial, '255' other
        int meteringMode = _directory.getInt(ExifDirectory.TAG_METERING_MODE);
        switch (meteringMode) {
            case 0:
                return "Unknown";
            case 1:
                return "Average";
            case 2:
                return "Center weighted average";
            case 3:
                return "Spot";
            case 4:
                return "Multi-spot";
            case 5:
                return "Multi-segment";
            case 6:
                return "Partial";
            case 255:
                return "(Other)";
            default:
                return "";
        }
    }

    public String getSubjectDistanceDescription() throws MetadataException
    {
        if (!_directory.containsTag(ExifDirectory.TAG_SUBJECT_DISTANCE)) return null;
        Rational distance = _directory.getRational(ExifDirectory.TAG_SUBJECT_DISTANCE);
        java.text.DecimalFormat formatter = new DecimalFormat("0.0##");
        return formatter.format(distance.doubleValue()) + " metres";
    }

    public String getCompressionLevelDescription() throws MetadataException
    {
        if (!_directory.containsTag(ExifDirectory.TAG_COMPRESSION_LEVEL)) return null;
        Rational compressionRatio = _directory.getRational(ExifDirectory.TAG_COMPRESSION_LEVEL);
        String ratio = compressionRatio.toSimpleString(_allowDecimalRepresentationOfRationals);
        if (compressionRatio.isInteger() && compressionRatio.intValue() == 1) {
            return ratio + " bit/pixel";
        } else {
            return ratio + " bits/pixel";
        }
    }

    public String getThumbnailLengthDescription()
    {
        if (!_directory.containsTag(ExifDirectory.TAG_THUMBNAIL_LENGTH)) return null;
        return _directory.getString(ExifDirectory.TAG_THUMBNAIL_LENGTH) + " bytes";
    }

    public String getThumbnailOffsetDescription()
    {
        if (!_directory.containsTag(ExifDirectory.TAG_THUMBNAIL_OFFSET)) return null;
        return _directory.getString(ExifDirectory.TAG_THUMBNAIL_OFFSET) + " bytes";
    }

    public String getYResolutionDescription() throws MetadataException
    {
        if (!_directory.containsTag(ExifDirectory.TAG_Y_RESOLUTION)) return null;
        Rational resolution = _directory.getRational(ExifDirectory.TAG_Y_RESOLUTION);
        return resolution.toSimpleString(_allowDecimalRepresentationOfRationals) +
                " dots per " +
                getResolutionDescription().toLowerCase();
    }

    public String getXResolutionDescription() throws MetadataException
    {
        if (!_directory.containsTag(ExifDirectory.TAG_X_RESOLUTION)) return null;
        Rational resolution = _directory.getRational(ExifDirectory.TAG_X_RESOLUTION);
        return resolution.toSimpleString(_allowDecimalRepresentationOfRationals) +
                " dots per " +
                getResolutionDescription().toLowerCase();
    }

    public String getExposureTimeDescription()
    {
        if (!_directory.containsTag(ExifDirectory.TAG_EXPOSURE_TIME)) return null;
        return _directory.getString(ExifDirectory.TAG_EXPOSURE_TIME) + " sec";
    }

    public String getShutterSpeedDescription() throws MetadataException
    {
        // I believe this method to now be stable, but am leaving some alternative snippets of
        // code in here, to assist anyone who's looking into this (given that I don't have a public CVS).

        if (!_directory.containsTag(ExifDirectory.TAG_SHUTTER_SPEED)) return null;
//        float apexValue = _directory.getFloat(ExifDirectory.TAG_SHUTTER_SPEED);
//        int apexPower = (int)Math.pow(2.0, apexValue);
//        return "1/" + apexPower + " sec";
        // TODO test this method
        // thanks to Mark Edwards for spotting and patching a bug in the calculation of this
        // description (spotted bug using a Canon EOS 300D)
        // thanks also to Gli Blr for spotting this bug
        float apexValue = _directory.getFloat(ExifDirectory.TAG_SHUTTER_SPEED);
        if (apexValue<=1) {
            float apexPower = (float)(1/(Math.exp(apexValue*Math.log(2))));
            long apexPower10 = Math.round((double)apexPower * 10.0);
            float fApexPower = (float) apexPower10 / 10.0f;
            return fApexPower + " sec";
        } else {
            int apexPower = (int)((Math.exp(apexValue*Math.log(2))));
            return "1/" + apexPower + " sec";
        }

/*
        // This alternative implementation offered by Bill Richards
        // TODO determine which is the correct / more-correct implementation
        double apexValue = _directory.getDouble(ExifDirectory.TAG_SHUTTER_SPEED);
        double apexPower = Math.pow(2.0, apexValue);

        StringBuffer sb = new StringBuffer();
        if (apexPower > 1)
            apexPower = Math.floor(apexPower);

        if (apexPower < 1) {
            sb.append((int)Math.round(1/apexPower));
        } else {
            sb.append("1/");
            sb.append((int)apexPower);
        }
        sb.append(" sec");
        return sb.toString();
*/

    }

    public String getFNumberDescription() throws MetadataException
    {
        if (!_directory.containsTag(ExifDirectory.TAG_FNUMBER)) return null;
        Rational fNumber = _directory.getRational(ExifDirectory.TAG_FNUMBER);
        return "F" + SimpleDecimalFormatter.format(fNumber.doubleValue());
    }

    public String getYCbCrPositioningDescription() throws MetadataException
    {
        if (!_directory.containsTag(ExifDirectory.TAG_YCBCR_POSITIONING)) return null;
        int yCbCrPosition = _directory.getInt(ExifDirectory.TAG_YCBCR_POSITIONING);
        switch (yCbCrPosition) {
            case 1: return "Center of pixel array";
            case 2: return "Datum point";
            default:
                return String.valueOf(yCbCrPosition);
        }
    }

    public String getOrientationDescription() throws MetadataException
    {
        if (!_directory.containsTag(ExifDirectory.TAG_ORIENTATION)) return null;
        int orientation = _directory.getInt(ExifDirectory.TAG_ORIENTATION);
        switch (orientation) {
            case 1: return "Top, left side (Horizontal / normal)";
            case 2: return "Top, right side (Mirror horizontal)";
            case 3: return "Bottom, right side (Rotate 180)";
            case 4: return "Bottom, left side (Mirror vertical)";
            case 5: return "Left side, top (Mirror horizontal and rotate 270 CW)";
            case 6: return "Right side, top (Rotate 90 CW)";
            case 7: return "Right side, bottom (Mirror horizontal and rotate 90 CW)";
            case 8: return "Left side, bottom (Rotate 270 CW)";
            default:
                return String.valueOf(orientation);
        }
    }

    public String getResolutionDescription() throws MetadataException
    {
        if (!_directory.containsTag(ExifDirectory.TAG_RESOLUTION_UNIT)) return "";
        // '1' means no-unit, '2' means inch, '3' means centimeter. Default value is '2'(inch)
        int resolutionUnit = _directory.getInt(ExifDirectory.TAG_RESOLUTION_UNIT);
        switch (resolutionUnit) {
            case 1: return "(No unit)";
            case 2: return "Inch";
            case 3: return "cm";
            default:
                return "";
        }
    }

    public String getSensingMethodDescription() throws MetadataException
    {
        if (!_directory.containsTag(ExifDirectory.TAG_SENSING_METHOD)) return null;
        // '1' Not defined, '2' One-chip color area sensor, '3' Two-chip color area sensor
        // '4' Three-chip color area sensor, '5' Color sequential area sensor
        // '7' Trilinear sensor '8' Color sequential linear sensor,  'Other' reserved
        int sensingMethod = _directory.getInt(ExifDirectory.TAG_SENSING_METHOD);
        switch (sensingMethod) {
            case 1:
                return "(Not defined)";
            case 2:
                return "One-chip color area sensor";
            case 3:
                return "Two-chip color area sensor";
            case 4:
                return "Three-chip color area sensor";
            case 5:
                return "Color sequential area sensor";
            case 7:
                return "Trilinear sensor";
            case 8:
                return "Color sequential linear sensor";
            default:
                return "";
        }
    }

    public String getComponentConfigurationDescription() throws MetadataException
    {
        int[] components = _directory.getIntArray(ExifDirectory.TAG_COMPONENTS_CONFIGURATION);
        String[] componentStrings = {"", "Y", "Cb", "Cr", "R", "G", "B"};
        StringBuffer componentConfig = new StringBuffer();
        for (int i = 0; i < Math.min(4, components.length); i++) {
            int j = components[i];
            if (j > 0 && j < componentStrings.length) {
                componentConfig.append(componentStrings[j]);
            }
        }
        return componentConfig.toString();
    }

    /**
     * Takes a series of 4 bytes from the specified offset, and converts these to a
     * well-known version number, where possible.  For example, (hex) 30 32 31 30 == 2.10).
     * @param components the four version values
     * @return the version as a string of form 2.10
     */
    public static String convertBytesToVersionString(int[] components)
    {
        StringBuffer version = new StringBuffer();
        for (int i = 0; i < 4 && i < components.length; i++) {
            if (i == 2) version.append('.');
            String digit = String.valueOf((char)components[i]);
            if (i == 0 && "0".equals(digit)) continue;
            version.append(digit);
        }
        return version.toString();
    }

    /**
     * The Windows specific tags uses plain Unicode
     */
    private String getUnicodeDescription(int tag) throws MetadataException
    {
         if (!_directory.containsTag(tag)) return null;
         byte[] commentBytes = _directory.getByteArray(tag);
         try {
             // decode the unicode string
             // trim it, as i'm seeing a junk character on the end
            return new String(commentBytes, "UTF-16LE").trim();
         }
         catch (UnsupportedEncodingException ex) {
            return null;
         }
    }

    public String getWindowsAuthorDescription() throws MetadataException
    {
       return getUnicodeDescription(ExifDirectory.TAG_WIN_AUTHOR);
    }

    public String getWindowsCommentDescription() throws MetadataException
    {
       return getUnicodeDescription(ExifDirectory.TAG_WIN_COMMENT);
    }

    public String getWindowsKeywordsDescription() throws MetadataException
    {
       return getUnicodeDescription(ExifDirectory.TAG_WIN_KEYWORDS);
    }

    public String getWindowsTitleDescription() throws MetadataException
    {
       return getUnicodeDescription(ExifDirectory.TAG_WIN_TITLE);
    }

    public String getWindowsSubjectDescription() throws MetadataException
    {
       return getUnicodeDescription(ExifDirectory.TAG_WIN_SUBJECT);
    }
}