 A Guide to Web Image Compression Software: HVS JPEGSoftware type: GIF/JPEG optimisers
Impressions:HVS JPEG is one of the better JPEG compressors, but it is also one of the more expensive. It comes as a Photoshop filter plugin, which means it should work with other graphics packages such as Paintshop Pro etc. The current demo program comes with a time limit on it. The Digital Frontiers people seem to have changed their minds from the previous demo, which would not allow you to export a modified image. The time limit version is a much better idea, allowing realistic comparison with other packages. Installation is simple, just copy a few files into the plugins directory. The program comes with a detailed help file and a PDF-format manual which tells you all you need to know. The program interface is good and easy to use. It allows you to compare a compressed image with the original, but not simultaneously - you need to switch between the two images, unlike programs such as Ulead Smartsaver and Web Graphics Optimizer, which show both original images and compressed image(s) together. Personally I like to see both images at once. There are two features that distinguish HVS JPEG from its competitors. The first is the ability to use different Q-tables as the basis for quality setting in the compressed image. The second is a pre-filtering option that sets up images to minimise compression artifacts. Q-tables are a reference used in the JPEG compression process that determine what things are compressed and how. HVS JPEG comes with three generic pre-optimised Q-tables, and the option to calculate an optimum Q-table for the particular image you are compressing. The three supplied tables are the standard JPEG Q-table (that the other packages presumably use), one optimised for portraits and other images with slowly varying colour and texture, and one for images with more rapid variation of texture. In general, selecting the right Q-table option correctly will give the best result for any particular picture, but, as I found and as the manual says, sometimes one of the other options does a better job than the one you might expect to use, so a little experimentation is called for. The second distinctive feature of HVS JPEG is the use of pre-filters to minimise artifacts. It presents you with a "sharp-soft" slider to set the scale of the softening, and a "strong-weak" slider, to set the level of the effect. There seem to be two ways of reducing colour smearing, blotchiness and "wrinklies" around high contrast boundaries, characteristic of over-compression. The first is to select certain areas of an image for lower compression - thereby ducking the problem. PiCoBello and JPEG Pro (and soon, I think, Pegasus) use this process. HVS JPEG takes the second approach, by softening edges before compression, to minimise the wrinklies. In my initial trials, while it gave slightly smaller file sizes, it didn't do such a good job as the area-select method. However, the benefits you get from either method will depend a lot on skill. If you're looking for quick compression, you probably won't use either method. Personally, I like to be able to tweak images. I still have a lot of experimenting to do with both methods. As soon as you try your initial compression in HVS JPEG, you realise that it is very much more computationally intense than other packages. This is due at least in part to Digital Frontiers' "human visual systems" approach to optimising images. I'm not sure what to make of this, and I think the effects may be fairly subtle for some images. I found the processing calculations take several seconds longer than average for a typical 40K image. As a general rule, it also produces better results than the other packages, with the exception, usually, of Pegasus' RapidVue. However, HVS JPEG has an easier interface than RapidVue. Then again, RapidVue is a lot cheaper... I suspect I'll use both at different times. I would definitely include HVS JPEG 2.0 in any shortlist of programs to trial. It is a more complex program than many of the others, but the more you use it, the better the results you'll get. Links to information about web graphics compression, palettes and related matters of interest. Back to graphics review page Back to the main entry page This information is Copyright © 1998 David Nicholls. These pages may be linked to, provided you don't embed them in frames, but may not be reproduced in any form without permission in writing from the author. |
HVS JPEG 2.0