Exif Formats (TIFF and JPG)

Exif is a standard for image files created with digital cameras and other input devices. The standard is set by the Japan Electronic Industry Development Association, and formally it is called the Digital Still Camera Image File Format Standard.

Exif files contain either uncompressed TIFF images or compressed JPEG images. In addition, these files can contain many comment fields of various types. You can use the LFile::ReadComment function to read comments in an existing file. Before writing a file, you can use the LFileSettings::SetComment function to create an array of comments to be saved in the file.

LEADTOOLS reads and writes the following Exif formats:

TIFF. This is a tag-based file format designed to promote universal interchanges of digital image data. You can save any image size.
JPG. This is the JPEG format with YUV 4:2:2 sampling. You can save any image size.
For more information, refer to Compression Using LEAD and JPEG Formats.

An Exif JPG file can also contain a stamp (thumbnail) image, which is a small copy of the main image. The stamp size has been restricted to 160x120x24. When saving Exif files, the StampWidth, StampHeight, and StampBits members of the SAVEFILEOPTION structure will be ignored and 160 (StampWidth), 120 (StampHeight) and 24 (StampBits) will be used instead. That limitation has been imposed in order to conform with the ExifR98 interoperability rules imposed by Japanese digital camera manufacturers.

If you are working with uncompressed (TIFF) Exif files, the stamp size is (width x height x 24 bpp), with no limitations on width and height.

NOTE: To save a region inside a TIFF file, you must have an unlocked Document, Vector, or Medical Imaging license.

To load a stamp image from a file, use the LFile::ReadStamp function.

NOTE: LEADTOOLS will currently write version 2.21 of these files. But it can read earlier or later versions as the file format is designed to be backward compatible.

File constants associated with these file formats are:

Constant	Read Support	Write Support	Description
FILE_EXIF	24 BPP	24 BPP	[96] Exif file containing a TIFF image, with no compression and with RGB color space.
FILE_EXIF_YCC	24 BPP	24 BPP	[97] Exif file containing a TIFF image, with no compression and with YCbCr color space.
FILE_EXIF_JPEG_422	24 BPP	24 BPP	[98] Exif file containing a JPEG compressed image and YUV 4:2:2 color space.
FILE_EXIF_JPEG_411	24 BPP	24 BPP	[101] Exif file containing a JPEG compressed image and YUV 4:1:1 color space.