Hints and Tips

Here are some useful techniques you can use to get the most out of JPEGView.


You can sacrifice quality and system response time for speed.

There are several techniques you can use to make JPEGView open and display images more quickly; however, as with all things, there are tradeoffs involved.  If you donÕt mind sacrificing a little bit of picture quality, you can gain a great deal of speed.  First, if youÕre working on a color system, set the default display quality to Normal (under the Drawing preferences); although JPEGViewÕs new dithering routines give superior quality, they are somewhat slower than the built-in routines that Apple provides.  Returning to normal quality will make scaling and dithering of images go faster.

If you are on a 256-color system, you can also gain a lot of speed by turning off two-pass color reduction (choose ÒNeverÓ under the ÒAutomatically reduce images to 16 or 256 colorsÓ options in the Drawing preferences).  Your images will look much grainier, but they only need to be decompressed once to be displayed.  Alternatively, if you donÕt mind working in grayscales, you can open the Monitors controls panel, and select ÒGrayscalesÓ.  JPEGView never does two-pass color reduction when displaying images on a grayscale device, and you get excellent quality with 256 grays.

Finally, if you donÕt mind slowing other applications down to a halt, you can set the ÒTime given to other applicationsÓ option to ÒMinimalÓ (under the Miscellany preferences).  This causes JPEGView to hog more of the processor time for drawing, making it work faster overall.


If you have memory, use it!  

Increase JPEGViewÕs memory as much as you can afford to (using the Get Info box from the Finder).  JPEGView comes initially set to use only 1024K of memory; although this is adequate for most basic operations, there is a great advantage to be gained by increasing the available memory.   When JPEGView has enough free memory, it will store an off-screen copy of the uncompressed image displayed on your screen, which will be used to redraw obscured parts of the window instantaneously.  If there is not enough free memory for this extra copy, JPEGView will have to decompress the image again before it can update an obscured window. 
 
In addition, if you use two-pass color reduction and give JPEGView enough memory for a 24-bit image the size of your screen, the image will only need to be decompressed once.  To give you an idea of how much memory is needed for optimal performance, here is a table of minimum recommended memory sizes for various monitor setups.  To determine how much memory you should give to JPEGView, take the value in the table appropriate for your monitor and add to that the compressed size of the largest image you would like to view.

For 256 colors with no color reduction:
   ¥ 12Ó monitors: 500K
   ¥ 13Ó monitors: 600K
   ¥ 16Ó/full-page monitors: 850K
   ¥ 21Ó/two-page monitors: 1300K

For 256 colors with color reduction, or for Millions of colors:
   ¥ 12Ó monitors: 1100K
   ¥ 13Ó monitors: 1600K
   ¥ 16Ó/full-page monitors: 2500K
   ¥ 21Ó/two-page monitors: 4300K

Note again that these memory values are not hard minimums; rather, they are the minimum memory needed to show optimum performance on single images.  The default allocation of 1024K is adequate for viewing almost any image less than 500K compressed, albeit with some speed degradation.

Also, note that if you have virtual memory, you should never give JPEGView more memory than the amount of real, physical RAM you have in your system.  Otherwise, your hard drive is going to go nuts while JPEGView tries to access more memory than you have!


Make good use of the Crop & Zoom feature in the View menu. 
 
There is a lot of power hidden in this innocuously titled feature!  In fact, the primary reason for it being there, believe it or not, is that it is a replacement for scroll bars.  With most image viewing utilities on the Macintosh, you are initially shown only a portion of the image, which you then must scroll around in, looking for whatever details youÕre interested in.  If youÕre lucky, maybe it will let you automatically scale the image to fit on your screen.  

JPEGView takes exactly the opposite approach: you are given the full image first, scaled to fit on your screen, with the option of zooming in on any part of that image.  To do this, you simply click and drag a selection rectangle on your image, and then select Crop & Zoom from the Edit menu.  Additionally, when used in conjunction with the Select Screen Area option in the Edit menu, you can automatically select a screen-sized chunk of the image to view at full resolution by simply dragging the selection rectangle anywhere in your image.  

This approach has three important advantages: first, you gain back all the screen area taken up by those annoying scroll bars in the window; second, you are not required to have enough memory to buffer the entire decompressed image at full resolution; and finally, rather than scrolling around helplessly wondering what you are looking for, you can see with your own eyes the full image and move the selection rectangle over the interesting portions.  It may not be the method youÕre used to, but I believe it is far more powerful than the standard scroll bars.


Create a folder of aliases to use for your slide show.

This technique allows you to choose exactly which images you want to display in your slide show without having to reshuffle your image collection.  Simply make aliases of all the images you want to have in your slide show, drag them all into a separate folder, and run the slide show from that folder.  JPEGView will automatically resolve the aliases and display the images as you would expect.


Make sure you convert JPEGs to JFIF format before posting and trading them!  

When swapping JPEG pictures with others Ñ and especially when uploading JPEGs to public access sites! Ñ always make sure you save the image as a JFIF file; otherwise, only Macintosh users will be able to read the file and youÕre liable to make some others upset!  You should also save JFIF images without custom icons and reduced color information Ñ this extra information tends to confuse some file transfer utilities!


Be careful if you are converting your GIFs to JPEGs!  

A heated and never-ending debate has been filling the Usenet over whether converting GIF files to JPEGs is a good idea.  Those opposed to the idea claim that JPEG was not designed to work with 256 (or fewer) color pictures and that JPEG only makes bad pictures look worse.  Proponents feel that the space savings gained more than makes up for any quality degradation, which becomes minimal for high-quality GIFs.  So, whoÕs right and whoÕs wrong?  Unfortunately, it depends on the GIF image.  For line drawings, cartoons, and GIFs with very few colors (16 or less), conversion to JPEG is usually a bad idea, as GIF compresses such images very well and JPEG will likely create some unwanted ÒnoiseÓ in the image.  For high-quality, 256-color GIF images, JPEG compression does pretty well and introduces little visible loss in image quality.  For other images, a judgement can only be made on an image-by-image basis.  The conversion issue is by no means clear-cut.