The JPEG format was developed to provide a high degree of compression for images. It is a "lossy" compression method, meaning that some color information from the original is lost. When saving JPEG files, ThumbsPlus allows you to specify the intended quality of the image. Several other formats, including .J6I (Ricoh camera) and .PMP (Sony camera) are standard JFIF files with a header. ThumbsPlus can usually locate the JFIF header and process these files.
JPEG is generally appropriate for photographed or scanned images, and works best for 24-bit sources. JPEG is generally inappropriate for any type of line-drawn art.
The JFIF specification describes a standard way to incorporate JPEG images in disk files; only JFIF images are supported by ThumbsPlus. Some software (notably GIF2JPG, by Handmade Software), writes non-JFIF files which ThumbsPlus cannot handle.
ThumbsPlus incorporates the Independent JPEG Group's source code (release 6). This includes support for reading and writing progressive JPEG files.
ThumbsPlus allows several loading options for JPEG files. When using a 256-color display, the JPEG file may be reduced to 256 colors during loading. This is not recommended if the image is going to be edited; too much color information is lost with dithering. See Options | File Loading - JPEG.
IPTC/NAA information, stored by Adobe Photoshop and other software, can be extracted from JPEG files and displayed in File | Properties - Info. ThumbsPlus retains the information if the file is written or converted to TIFF format.
For more information on saving in the JFIF format, see JPEG Save Options.