An introduction to OS 4 picture datatypes
by Oliver Roberts

The concept of datatypes made its debut on AmigaOS in Release 3.0, making it possible for applications to read virtually any type of data file (pictures, sound, movies, and so on) with ease, for which a suitable datatype class is available, through a common object-orientated API. To a certain extent, this helped alleviate the need for application writers to spend time developing their own custom decoding routines and also meant that applications could load any type of data transparently without needing to modify the application at all.

Arguably, the most common and important type of data file handled by datatypes are pictures, and with this being my area of expertise, this article concentrates on this area. These days we take datatypes for granted, but imagine if you were restricted to using ILBM images! Seems unlikely, albeit until AmigaOS 3.0 this was not so unthinkable, when applications had to deal with decoding image data themselves - the datatype system in turn made it extremely easy for applications to load images using the users' preferred image file formats.

Picture datatypes are used in various OS 4 components more than ever before - not only just for Workbench backdrops and by Multiview, but the new Intuition GUI relies on datatypes to load images too. Datatypes are also utilised by IBrowse, which will always fall back to attempting to load an image via datatypes if it cannot handle an image itself (it's not uncommon for websites to use inline BMP images, for example).

In the past, the trend has been that picture datatype classes have been developed and supplied by third parties, with the only type of picture readable on a vanilla installation of AmigaOS 3.1 being ILBM images (and then only up to 8-bit). Obviously, being the traditional file format used for images on the Amiga, this type of file had to be supported. Unfortunately, it was then left up to the user to find and install third party datatypes to allow him/her to view other types of images through the datatype system. Thankfully, AmigaOS 3.5 and 3.9 did provide JPEG and GIF datatypes, although neither of these made use of the PowerPC processor which was supported in the OS at that time by the inclusion of WarpUp - this was a disappointment to many BlizzardPPC and CyberstormPPC users, including myself.

JPEG images in particular use a CPU intensive compression scheme. Back then, I was not satisfied with any of the existing JPEG datatypes, and knew it was possible to make a JPEG datatype utilising the PPC which could decode images much faster. And that is where my involvement in developing picture datatypes began in earnest four years ago, with the end result being the Warp Datatypes (WarpDTs). Over the years, the WarpDTs have matured from simply being a fast PPC JPEG and PNG datatype solution into a whole family of datatypes using the same fundamental engine and design principles, rock solid stability, greatly improved support for far more types of images and extensive support for both 68K and PPC.

In my opinion, it is very important that OS 4 provides support for commonly used image types, including not only ILBM, but JPEG and PNG especially. Consequently, brand new JPEG, PNG, TIFF and BMP datatypes have been specifically developed for OS 4 (these are accompanied by PPC ports of the existing GIF and ILBM datatypes, and of course the picture datatype superclass). Needless to say, these four new datatypes are heavily based on the WarpDT code, so therefore share a very similar feature set. Additionally, since the datatypes are targeted specifically for OS 4, it has allowed certain assumptions to be made, making it possible to streamline various parts of code, increasing efficiency and speed.

Everyone is no doubt familiar with JPEG images, but probably less so with PNG - a flexible modern file format offering some unique and impressive features, originally cited as a replacement to GIF. However, PNG is much more than that. Unlike JPEG, PNG offers lossless compression, which offers far better compression ratios than the relatively simple RLE compression used by ILBM files. Obviously, better compression implies a speed trade off, although this is really a comparative non-issue for PPC implementations. Despite its advantageous qualities, PNG is often conveyed as being unpopular, largely due to slow take up and limited support by other OS and software vendors. However, Amiga users have been fortunate in that many existing applications embraced the PNG image format early on. Until this time AmigaOS has not provided PNG support, but with the addition of a PNG datatype as standard for OS 4, hopefully developers and users will feel more comfortable in using PNG as a viable format for image storage.

Although TIFF and BMP files are not commonly used to store images by AmigaOS applications, they are used frequently on other platforms, so with OS 4 supporting these types of images it means that users can easily transfer images from other systems to their Amiga, without having to worry about converting them to a different image format. Third-party TIFF support for AmigaOS has always been somewhat sub-standard, with other datatypes only being able to load a small subset of TIFF files, being very slow or just plain broken. In contrast, due to its WarpTIFF origins, the OS 4 TIFF datatype offers by far the largest coverage of the TIFF specification available for AmigaOS and moreover is able to load images efficiently, at speed.

Given that the WarpDTs are so highly optimised and are comparatively fast even on 68K, the OS 4 datatypes should be an absolute dream to use on the AmigaOne, and I for one am looking forward to this prospect. And what's more, the OS 4 datatypes are largely already completed, and are being tested on the CyberstormPPC version of OS 4 without any problems.

Anyway, I hope you have enjoyed my take on this distinct slice of the OS 4 feature set. For more information on the WarpDTs and/or if you would like to try out the latest versions for AmigaOS 3.x, see the WarpDT pages.