JPEGView doesn’t 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 Hints and Tips entitled “Make good use of the Crop & Zoom feature” 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 — I repeat — not my fault! The solution is quite simply to upgrade to QuickTime 1.5, 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. Nobody’s perfect!
• Where can I get the latest version of QuickTime?
Apple’s 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 “anonymous”, and give your email address as a password. The latest version should be in the /dts/mac/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.
• Why can’t JPEGView convert between formats other than JFIF and QuickTime?
• Why can’t JPEGView create new images?
• Why can’t JPEGView print my images?
• Why can’t 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 As dialog — saving cropped PICTs and saving quantized image palettes — are all there for the purpose of improving the on-screen viewing of JPEG images. And its ability to add previews to QuickTime PICT 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 you’ll find that its special features, low memory requirements, and overall stability are a direct result of keeping its feature set under control.
• Why don’t my windows update when I uncover them?
This is a feature of JPEGView’s slow window updating. See the section on “Fast and Slow Window Updates” in the Viewing Images section of this documentation for a precise description of what’s going on.
• Why is dithering giving me crummy results on some images?
In brief, because Apple’s built-in dithering seems to have trouble with images when the system’s colors are matched pretty closely with what colors are in the image. For a more detailed explanation, see the Hints and Tips section titled “Avoid dithering, if possible”.
• Why don’t my JPEGView GIF documents have icons?
If you upgraded from a previous version of JPEGView, which did not handle GIF files, then the Finder doesn’t 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 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 quantization and for the JPEGView code itself. The reason for this is that while the current slide is displayed, JPEGView likes to 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 256k of overhead.
• Why aren’t the system colors restored when I switch out of JPEGView?
The Macintosh supports a fairly sophisticated means of managing the colors that are available to an application. JPEGView, unlike most applications, is rather picky about which colors it gets, which is why you always see the colors change when you load up an image with a custom palette. Other applications, most notably the Finder, don’t really care which colors they get. Thus, when you switch from JPEGView to another application which doesn’t need any special colors, the system will notice that and do nothing to change the colors back to the default system colors. This is normal behavior, not a bug in JPEGView.
• Why are progress updates so erratic with JPEG images?
This is one of QuickTime’s “features”: you tell it what subroutine to call for progress updates, and it’s supposed to call it regularly. Unfortunately, this doesn’t always happen as regularly as I’d like, but there’s nothing I can do to fix it. C’est la vie. QuickTime 1.0 is particularly notorious for this problem; QuickTime 1.5 shows a marked improvement, but things could be better.
• Why can’t I select an area to zoom in a full screen window?
The very nature of a “full screen window” violates Apple’s rules for how applications are supposed to do things, primarily because it removes the menu bar from the screen. In order to prevent confusion when using these windows, I have set it up so that clicking the mouse button restores the menu bar and allows you access to the menus. The tradeoff here is that any mouse clicks received in a full screen window must bring the menu bar forward and therefore cannot be used to make a selection.
• What is banding?
Banding is a technique used by Apple’s QuickTime to allow you to compress large JPEG images in a small amount of memory. Essentially, all it involves is dividing the image vertically into several strips, or “bands,” 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, there is currently only one known FTP site which officially carries JPEG files and, unfortunately, it is very small and in Finland. For now at least, the BBS community is probably the best place to look. Additionally, those with Usenet access can check out the alt.binaries.pictures newsgroups, which carry an unending stream of both JPEG and GIF files. Already JPEG is becoming more and more prominent in these forums, and it is not unreasonable to expect more sources to appear for such images in the very near future.
• Where can I get GIF pictures?
If you’re on the Internet, you’re 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 you’re bound to find some!
