In previous articles, we saw how to retrieve Image metadata and information. In this post we shall see how Sanselan guesses the Image format. We shall take it in two steps

• First we shall look at the ImageFormat class
• Then, we shall look into the implementation guessFormat() API

ImageFormat class

org.apache.sanselan.ImageFormat Class has three members name, extension and actual. Name and extension are same, however I am not sure I understand the use of actual variable.

The class has list of formats (including Unknown) supported by the library. They are all instances of ImageFormat class. The list is

1. IMAGE_FORMAT_UNKNOWN
2. IMAGE_FORMAT_PNG
3. IMAGE_FORMAT_GIF
4. IMAGE_FORMAT_ICO
5. IMAGE_FORMAT_TIFF
6. IMAGE_FORMAT_JPEG
7. IMAGE_FORMAT_BMP
8. IMAGE_FORMAT_PSD
9. IMAGE_FORMAT_PBM
10. IMAGE_FORMAT_PGM
11. IMAGE_FORMAT_PPM
12. IMAGE_FORMAT_PNM
13. IMAGE_FORMAT_TGA
14. IMAGE_FORMAT_JBIG2

guessFormat API – Under the hood

The guessFormat() API looks at the initial 2 to 4 bytes, also known as magic numbers, to determine the Image Format.

Algorithm is as follows:

• Read first two bytes
• Match with existing set of magic numbers and determine format
• It use byte 3 and 4 to determine format for JBig2

The list of magic numbers for different formats is as follows

In addition to this IMAGE_FORMAT_JBIG2 format, byte 3 must be equal to 0x42 and byte 4 must be equal to 0x32.

Based on this table, Sanselan recognizes the Image format. If the magic numbers don’t match from the one in the table, it returns IMAGE_FORMAT_UNKNOWN

References

Sanselan.java

In this article we shall see how to get Image metadata using Apache Sanselan.

Let’s see how the code looks

public static void main(String[] args) {
    String imageFile = args[0];
    try {
         // Metadata details
         IImageMetadata meta = Sanselan.getMetadata(new File(imageFile));
 
         System.out.println("--- Image Metadata ----");
         System.out.println(meta);
     } catch (ImageReadException e) {
         e.printStackTrace();
     } catch (IOException e) {
         e.printStackTrace();
     }
}

Most of the work is done in single line ?

getMetadata() API returns the IImageMetadata details. The toString() method of actual instance class of IImageMetadata prints the image information in a formatted fashion. The instance depends upon the format of the image.

Running the program on one the images shipped with Sanselan source produced this output

--- Image Metadata ----
Exif metadata:
Root:
Image Description: '’'
Make: 'Oregon Scientific'
Model: 'DS6639'
Orientation: 1
XResolution: 72
YResolution: 72
Resolution Unit: 2
Software: 'Adobe Photoshop 7.0'
Modify Date: '2008:07:13 21:05:34'
YCbCr Positioning: 2
Exif Offset: 228

Exif:
Exposure Time: 10/10266 (0.001)
FNumber: 28/10 (2.8)
Exposure Program: 2
ISO: 55
Exif Version: 48, 50, 50, 48
Date Time Original: '2003:10:20 09:01:29'
Create Date: '2003:10:20 09:01:29'
Components Configuration: 1, 2, 3, 0
Compressed Bits Per Pixel: 2
Brightness Value: 9
Exposure Compensation: 0
Max Aperture Value: 3
Metering Mode: 1
Light Source: 0
Flash: 0
Focal Length: 864/100 (8.64)
Subject Location: 27556, 57533, 60147, 20319
Flashpix Version: 48, 49, 48, 48
Color Space: 1
Exif Image Width: 300
Exif Image Length: 225
File Source: 3
Scene Type: 1
Custom Rendered: 0
Exposure Mode: 0
White Balance: 1
Digital Zoom Ratio: 1
Focal Length In 3 5mm Format: 42
Scene Capture Type: 0
Gain Control: 0
Contrast: 0
Saturation: 0
Sharpness: 0

Sub: (jpegImageData)
Compression: 6
XResolution: 72
YResolution: 72
Resolution Unit: 2
Jpg From Raw Start: 838
Jpg From Raw Length: 6258

Photoshop (IPTC) metadata:
Caption/Abstract: ?

In this article we shall see how to get Image Information using Apache Sanselan.

Let’s see how the code looks

public static void main(String[] args) {
String imageFile = args[0];
System.out.println("Image File = "+imageFile);
try {
ImageInfo imageInfo = Sanselan.getImageInfo(new File(imageFile));
System.out.println(imageInfo);
} catch (ImageReadException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
}

Most of the work is done in single line

getImageInfo() API returns the ImageInfo details. The toString() method of ImageInfo class prints the image information in a formatted fashion.

Running the program on one the images shipped with Sanselan source produced this output

The ImageInfo class can be used programtically to arrange files, or for other purposes as well

References

Sanselan Source

Sanselan Wiki