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RISC OS 3 User Guide


RISC OS 3.7 User Guide

23 - ChangeFSI

ChangeFSI is a useful program for converting and displaying image files of various formats. These images can then be converted into sprites or JPEGs for viewing with RISC OS applications such as !Paint and !Draw.

ChangeFSI stands for 'Change Floyd Steinberg Integer' (ChangeFSI performs Floyd Steinberg error diffusion dithering).

You should make sure that your conversion and subsequent use of an image does not infringe on any copyright that the image may be under.

ChangeFSI can read image data, scale the data to improve an image, change the x and y size, sharpen an image and write the result using error diffusion dithering in one step (so it provides the best possible quality). All operations are carried out with 32-bit fixed-point numbers (three per pixel in the case of a colour picture).

Starting ChangeFSI

ChangeFSI is in the Utilities directory on your hard disc or network. To start the application, double-click on the !ChangeFSI icon.

Using ChangeFSI

  1. Display the directory that contains the file for the image to be processed.
  2. Choose whether to save the image as a sprite or JPEG file.
  3. Change to a desktop screen display mode that you wish to view and store the image in, if you're exporting to a sprite.
  4. Drag the image file's icon onto the ChangeFSI application on the icon bar.

ChangeFSI automatically converts the file to give the best possible screen image for any display mode. For example, if you choose a 32-thousand colour mode ChangeFSI will produce an image with 32 thousand colours; if you only choose a 16-colour display mode ChangeFSI will produce a 16-colour image - if the colours are nearer to the greys than the colours in the 16-colour palette, it may be that the image is displayed in monochrome on a 16-colour display, but this doesn't mean that the colour information has been lost (unless you save the image as a sprite in that mode).

ChangeFSI then attempts to convert the file to give a RISC OS sprite, or a JPEG file, displaying the result.

Note: ChangeFSI may not retain transparent sprite pixels during processing. Transparent pixels can be changed to a colour, depending on the screen mode (e.g. transparent pixels in a 16-colour sprite become white in a 256-colour sprite).

Picture formats

ChangeFSI can convert many types of images to a sprite or JPEG file. These include the PC graphics formats TIFF, PCX (though not 1 bpp images, which may be converted to blank white sprites), PIC and IMG, the Amiga format IFF, the Compuserv GIF format and the JPEG format. See the later section Image file conversion for a full list.

ChangeFSI can also convert sprites or JPEGs from one display resolution into another. Be careful, though: every time you recompress a JPEG file it loses some information. Process a file first, and only save it as a JPEG once, right at the end.

There are some JPEG files available which don't conform to the standard convention. Although some of these files are accepted by !ChangeFSI, others will not be. If you find this to be the case try setting the file's type to JPEG (C85) before giving it to !ChangeFSI.

Additional information

The information in this chapter gives an overview of how ChangeFSI works from the desktop. Additional information in the form of text files is held within the application. If you want to read these files, shift double-click on !ChangeFSI to open the application directory, then open its Documents directory and double-click on one of the text files.

Files and what's in them:

A couple of hints on memory usage

If you are short on memory, Drag the Next slot (in the Tasks display window) down to 320k. If you are converting wide images (e.g. PhotoCD images up to 3072 pixels wide) increase the Next slot to 500k or more.

Icon bar menu options

This section tells you how to use ChangeFSI's menu options.

Scaling options

The Scaling options set which scale factor you wish to apply to your image. You can also transform, rotate or mirror the image.

Processing options

The Processing options control the image processing used in the conversion and display of the image. You'll notice that all of these options are 'off' by default; you will not normally need to change these settings.

Output options

The Output options control output to JPEG, or the screen mode in which sprites are created.

Sprite Output options

To output an image in sprite format, choose Sprite Output from the icon bar menu and set up the output options

JPEG Output options

To output an image in JPEG format, choose JPEG Output from the icon bar menu and set up the output options:


This option reprocesses the file according to any new options you may have set.


This option speeds up the processing of the image by blanking the screen during processing. If there is no benefit to be had from doing this, the option will be greyed out.

Save Choices

This option will save any changes you have made to the ChangeFSI options so that you can use these options as your default options next time you run ChangeFSI.


This quits the application, removing it from the icon bar.

Image menu options

Once your image has been produced you can press Menu over the image to display a menu of information about the input and output images.
The most important option is to save your processed image using the standard RISC OS Save as window.

Image file conversion

ChangeFSI will convert any of the following image formats into the sprite or JPEG format. You can choose the type of RISC OS sprite that is created by setting the Output Options. If no special output mode is chosen, ChangeFSI produces a sprite that is compatible with the current display mode.

Image types and how to recognise them:

Note: If you get a 'Number to big' error message while trying to display a TIFF file, or 'Division by zero' with an IFF file, then try setting the 'Ignore source pixel size' and/or 'Ignore pixel size' options. Also try setting these options if the proportions of an image (for example from an IMG file) are not what you expect.

RISC OS 3.7 User Guide - 22 JAN 1997

This edition Copyright © 3QD Developments Ltd 2015
Last Edit: Tue,03 Nov 2015