Although JPEGView has been designed primarily as an image viewer, it also sports the ability to convert image files between the standard JFIF format and the Macintosh’s own QuickTime JPEG format, as well as options for creating previews, for pre-calculating color quantization, and for saving cropped image files. Note that only JPEG-compressed files may be saved with JPEGView; other compression schemes are supported only for viewing. You will know whether you are able to save the current image by checking the Save As… item under the File menu; if it is dimmed, then JPEGView cannot save the active image.
File formats in the save dialog
When you choose the Save As… item from the File menu, you are presented with a standard save file dialog, with a few extra options appended to the bottom. Anything that looks familiar works as usual. The remaining options allow you to choose the output file format or to include additional data with the image file. Additionally, by checking the “Close when finished” box, you can instruct JPEGView to immediately put away the image after it has finished saving it.
There are three output file formats that JPEGView currently supports: QuickTime PICT, JFIF, and PICT0. More details concerning the properties of the PICT and JFIF file formats can be found in the File Formats and File Types section elsewhere in this documentation. The oddball format available here is the PICT0 format, which is the same format that is specified for color startup screens on the Macintosh.
Now, before you rush out and try to create a startup screen in this way, be warned that unfortunately it doesn’t work. The system will try to load the startup screen before QuickTime is loaded, and you’ll only end up with an ugly black and white icon. In fact, I was just about to remove support for PICT0 altogether until I heard that a PICT0 file can be properly used by the shareware extension DeskPict as a backdrop for your desktop. In fact, since this is the only known use of a compressed PICT0, JPEGView saves such files with the proper file type (SCRN) needed by DeskPict.
Under certain circumstances, JPEGView won’t allow you to save an image in JFIF format. This most commonly occurs when you try to save a cropped or a banded image. Both of these types of images have been modified in such a way that is not easily transported to the JFIF format. The only way to remedy the situation would be to decompress and then recompress the image using a third-party image manipulation tool. For banded images, this would seam the bands together into a single stream; for cropped images, this would permanently remove the hidden area of the cropped image.
Saving modified images
One of JPEGView’s more useful features is the ability to save cropped JPEG files as QuickTime PICTs without the need for recompressing the data. This is possible because the PICT file format stores not only the image data itself, but also information describing which portion of the image is to be displayed. Although this means that you save no space on your hard drive when you save a cropped image, it also means that you can at any time remove the cropping from the image, with no ill effects. Further, you save the time and quality degradation that accompanies the recompression of the image once the cropping is finished.
If you have selected either PICT or JFIF output for your image, you can choose to create and save a preview image. This preview image is simply a smaller representation of the full image, allowing you to quickly see what the image is without having to decompress the whole thing first. QuickTime automatically supports viewing of PICT preview images in the Open dialog; however, there is currently no official support for viewing JFIF preview images in the same way.
Finally, if you have told JPEGView to calculate a custom palette with its two-pass quantization, then you will be given the option to save that palette with a PICT or PICT0 image. What this means is that when opening this image in the future, JPEGView and certain other image viewers can detect and make use of this palette without having to slog through the time-consuming quantization. Note that you must configure JPEGView properly in order to prevent the two-pass quantization from being used all the time; see the section Preferences Settings for details on how this is accomplished.
The final result
Once you have entered a filename and have chosen your desired options, click on the Save button to perform the operation. If you chose to create a preview, a progress dialog will appear to keep you updated on the status of the preview creation; otherwise, JPEGView will perform the save operation quickly and quietly. The final image file will have a simple JPEGView icon, rather than the custom tiny picture that is automatically produced by some other QuickTime image utilities. The primary advantage of the simple icon is speed, though I would be willing to allow the creation of these custom icons in a future version, if there was sufficient demand.
