JPEGView/Resources/Help Text/12.JPEGView Q&A

JPEGView Questions and Answers


Why canÕt my friends read the JPEG files I give them?

The problem with transferring JPEG files from the Macintosh to another system is twofold.  First, most Macintosh JPEG files are stored as QuickTime PICTs, rather than as standard JFIF files.  So, if youÕre running into difficulties, first make sure you use JPEGView to save any JPEG image as a JFIF image.  The second problem has to do with file transfers; if you save custom icons or custom color sets with your JFIF image, it creates resources in the JFIF file that might cause problems when transferring those files.  To be absolutely safe, make sure that you turn off custom icons and custom color sets before saving your JFIF file (previews are still okay, however).


Why doesnÕt the JPEGView JFIF Preview icon show up when I start my system?

The JPEGView JFIF Preview extension isnÕt really a standard extension, in that it doesnÕt execute any code at startup.  Rather, it is a QuickTime component, which means that QuickTime looks for it in the Extensions folder, and automatically loads and uses it whenever it needs to view a JFIF preview.  Since it doesnÕt execute anything at startup, the extension doesnÕt display an icon at the bottom of your screen.  However, it is still working to provide access to JFIF previews.


Why doesnÕt JPEGView have scroll bars?

JPEGView doesnÕt use scroll bars for two very good reasons: first, with scroll bars you have to have enough memory to buffer the entire decompressed image at full resolution, which makes the memory requirements phenomenally high for 24-bit JPEG images; and second, JPEGView implements a Crop & Zoom feature which provides the same functionality as scroll bars but with several important advantages.  The section in the Hints and Tips chapter entitled ÒMake good use of the Crop & Zoom featureÓ explains these advantages in more detail.


Why does JPEGView crash when loading corrupted JPEG images?

This problem with terrible crashes was a result of loose error checking in the QuickTime 1.0 JPEG decoder.  This is not Ñ I repeat Ñ not my fault!  The solution is quite simply to upgrade to the latest version of QuickTime (version 1.6.1 as of December 1993), which is far more robust in handling damaged JPEGs.  And yes, there are some images out there that are bound to crash the new version on occasion.  NobodyÕs perfect!


Where can I get the latest version of QuickTime?

AppleÕs plan for QuickTime seems to include making it as widely available as possible.  If you have ftp access, just ftp to ftp.apple.com, login as ÒanonymousÓ, and give your email address as a password.  The latest version should be in the /dts/mac/sys.soft/quicktime directory.  Otherwise, you may want to check with your local Apple dealer (bring a blank floppy with you), who might be willing to copy it for you.  Also, check your local BBS systems.


Where can I get a copy of AppleScript?

Unlike QuickTime, AppleScript does not come absolutely free.  At present, the only two viable avenues for obtaining AppleScript are by ordering it from APDA, in which case it will cost you $20 plus tax and shipping, or by picking up the very recent and very well-written The Tao of AppleScript, written by Derrick Schneider and published by Hayden Books.  This latter option is probably the best for those just getting started with AppleScript, as it includes not only a good introduction to the AppleScript commands and functionality, but also a copy of the AppleScript extension and some scripting software for $25.


Why canÕt JPEGView convert between formats other than JFIF and QuickTime?
Why canÕt JPEGView create new images?
Why canÕt JPEGView map my image onto a complex three-dimensional object?

JPEGView is called JPEGView for a very good reason: it was written as an image viewer, not as an image conversion package.  Its ability to convert between JFIF and QuickTime PICT format is simply there as a convenient means of adding/removing the QuickTime PICT header; no additional compression or decompression of the image is involved.  Its features in the Save dialog Ñ saving cropped PICTs and saving reduced color sets Ñ are all there for the purpose of improving the on-screen viewing of JPEG images.  And its ability to add previews and icons to images is implemented to allow you to see in advance what you will be viewing on your screen.  One of the primary reasons for adding GIF support was to lessen the need to convert all GIF files to JPEGs.  All of this adds up to sharpen the focus of JPEGView as an application; I think youÕll find that its special features, low memory requirements, and overall stability are a direct result of keeping its feature set under control.


Why are my windows filled with strange patterns of dots?

Because JPEGView has marked that window for slow updating, meaning that the image is going to need to be decompressed again before it can be displayed.  See the section on ÒFast and Slow Window UpdatesÓ in the Viewing Images chapter for a precise description of whatÕs going on.


Why donÕt some of my JPEGView documents have icons?

If you upgraded from a previous version of JPEGView, which did not handle some of the more recent types of image files, then the Finder doesnÕt realize that the new version supports them.  To solve this, simply rebuild your desktop by holding down the Command () and Option keys during startup.


Why does JPEGView run out of memory during a slide show?

When JPEGView runs a slide show, it needs to have enough memory to hold two compressed images in memory simultaneously, in addition to any memory needed for color reduction and for the JPEGView code itself.  The reason for this is that while the current slide is displayed, JPEGView will prepare the next image for display, in order to help minimize the delay between slides.  Thus, to ensure that you have enough memory to run your slide show, make sure you give JPEGView enough memory to hold the two largest compressed images in memory, plus about 500k of overhead.


Why are the progress percentages so erratic with PICT images?

This is one of QuickTimeÕs ÒfeaturesÓ: you tell it what subroutine to call for progress updates, and itÕs supposed to call it regularly.  Unfortunately, this doesnÕt always happen as regularly as IÕd like, but thereÕs nothing I can do to fix it.  CÕest la vie.  QuickTime 1.0 is particularly notorious for this problem; QuickTime 1.5 and later shows a marked improvement, but things could still be better.


What is banding?

Banding is a technique used by AppleÕs QuickTime to allow you to compress large JPEG images in a small amount of memory.  Essentially, it involves dividing the image vertically into several strips, or Òbands,Ó and compressing them separately.  Unfortunately, this also makes them rather difficult to reassemble, except in the context of the QuickTime PICT format.  For this reason, banded images cannot be converted to JFIF files.


Where can I get JPEG pictures?

On the Internet, you can now find JPEG pictures via anonymous FTP at the Washington University archives (wuarchive.wustl.edu).  Simply log in as ÒanonymousÓ, give your email address as a password, and begin poking around.  Additionally, those with Usenet access should check out the alt.binaries.pictures newsgroups, which are becoming more and more dominated by full-color JPEG images every day. 

Where can I get GIF pictures?

If youÕre on the Internet, youÕre in luck: check out the GIF archives of wuarchive.wustl.edu via anonymous FTP (give your email address as the password).  There are also quite a lot of BBS systems that carry GIF files.  Look around and youÕre bound to find some!