The two most important factors in image file formats that affect their ability to support large images are as follows:

• Maximum allowed image dimensions. This usually depends on the integer format used for storing image dimensions.
• File size limitation. This usually depends on the integer format used for storing lengths or offsets to various data in the file. If a file is stored compressed, image size after decompression may be greater than the maximum supported file size.
  • Some file formats have limitations on blocks (chunks, strips) of pixel data, but allow multiple such blocks to exist in a file, and thus avoid the limitation on the file size.

The table below lists some of the popular file formats and their capabilities for storing gigabyte-sized images.

Image Format	Max Available Image Dimensions (width x height, in pixels)	Approximate Max Image Size, When Uncompressed (for a 24-bit RGB image)	Approximate File Size Limit
JPEG, EXIF-JPEG	65535 x 65535	12 Gb	None
TIFF, EXIF-TIFF	2^32-1 x 2^32-1	3 * 2^24 Tb	4 Gb 1
JP2, JPX	2^32-1 x 2^32-1	3 * 2^24 Tb	None
PSB	300 000 x 300 000	250Gb	None
PSD	30 000 x 30 000	25Gb	4 Gb
BMP	2^31-1x 2^31-1	3 * 2^20Tb	4 Gb
PNG	2^32-1 x 2^32 - 1	3* 2^24Tb	None
DICOM	65535 x 65535	12 Gb	2 Gb
PBM / PGM / PPM / PNM	None	None	None
TGA	65535 x 65535	12 Gb	4 Gb

¹ TIFF format uses 32-bit unsigned integers to store data offsets and sizes. As a result, a strip of pixel data in a TIFF image cannot be stored at an offset greater than 4 Gb, and its size formally cannot be greater than 4 Gb. Thus, the size of the largest compliant TIFF image can be a bit less than 8 Gb. This assumes that two strips of nearly 4 Gb size are used.

ImageGear supports the reading and writing of single-page, single-strip, single-tiled uncompressed TIFF images where strip byte counts are greater than 4 Gb. If the size of a strip exceeds 4 Gb, ImageGear writes 0 to the StripBytes tag. The reader can calculate strip size from image dimensions in such a case.
Note, though, that such files are formally incompliant and may not be supported by other readers.

When writing a gigabyte-sized TIFF image, make sure to keep the IMAGE_BEFORE_IFD TIFF control parameter set to its default value of FALSE.