RISC OS 3.7 User Guide
30 PhotoView 
PhotoView is a PhotoCD sample application which allows you to access the images on a PhotoCD disc. It is not supplied on all machines.
Using PhotoView to view and manipulate an image you can
- choose the display resolution of the selected image
- rotate the image through 0, 90, 180 and 270 degrees
- flip the image in the vertical plane prior to rotation
- export the image in a choice of image formats
- save the image, or a selected area or the image, in a choice of image formats.
Starting PhotoView
PhotoView is in the Utilities directory on your hard disc or network. To start the application, double-click on the ! PhotoView icon. The application icon appears on the icon bar.
Loading a contact sheet
A contact sheet is a PhotoCD directory display which contains a number of thumbnail images. A thumbnail is a small representation of an image; there is one thumbnail for each image stored on the PhotoCD disc. Thumbnails are numbered in order corresponding to the number of the stored image on the PhotoCD.
To open a contact sheet, click on the PhotoView icon on the icon bar. Alternatively, if you have more than one PhotoCD available, press Menu over the PhotoView icon bar icon, and choose the directory you want from the Source submenu:
The contact sheet for the selected PhotoCD is opened on the desktop:
Loading an image
Choose the image you want to load by clicking on its thumbnail. This opens a Control window containing the same thumbnail:
You use the control window to choose image display settings prior to displaying the image itself.
You can control
- the resolution at which the image will be displayed
- the orientation in which the image will be displayed
- the palette to be used to generate the image
- the use of dithering in the image generation.
The control window also displays the colour details (the colour depth in bpp, and the display resolution in dpi) of the current display mode.
Note that you cannot alter the current display mode within the control window.
Changing image resolution
It is a good idea to work with a low resolution image in the desktop, and then export at a higher resolution if required. The higher the resolution of an image, the larger the size of that image, and the longer it takes to load and manipulate.
To change the resolution at which the image will be displayed:
- 1 Click on the menu icon to the right of the box containing the current resolution setting.
- 2 Choose the new resolution from the list displayed.
Changing image orientation
By default, orientation is set to 0 degrees for a landscape image, and 90 degrees or degrees for a portrait image. To change the orientation at which the image will be displayed, click on the menu icon to the right of the box containing the current orientation setting. The list of orientations displayed includes four options with which you can flip the image in the vertical plane prior to rotation. Choose the new orientation from this list.
Changing the default palette
By default, the palette used to generate the image is the default WIMP palette for the current display mode. To change the palette, click on the menu icon to the right of the box containing the current palette details, and choose another palette from the list displayed.
Enabling and disabling dithering
By default, dithering during image generation is enabled. If you wish to change this setting, simply click on the button displaying the current setting. The legend on this button will toggle between a tick and a cross to indicate whether dithering is enabled or disabled.
Displaying an image
To display an image:
- 1 Load the image by clicking on its thumbnail.
- 2 Set the display options you want to use, bearing in mind that the higher the resolution setting, the larger the size of the image, and the longer it will take to load and manipulate.
- 3 Click on OK (if at this point you don't want to continue, click on the control window's Cancel button instead).
Manipulating a displayed image
Once you have displayed the image, further options become available via the Image menu. To display the Image menu, click Menu anywhere within the displayed image window.
The menu has the following options:
- Image info gives image details extracted from information pressed on the PhotoCD disc at the point at which the disc was pressed.
If the disc was pressed in a single session, the Last Modified box contains a dash, otherwise it contains the date when the last session was written.
If a copyright file is contained on the disc, the copyright filename is shown in the appropriate box. You can view the copyright information by clicking in the Read Rights button at the bottom of the window. If no copyright file is present, the Read Rights button is greyed out.
- Save displays a Save as box which allows you to save the image as a sprite file appropriate to the current display mode.
- Export displays the Export menu which offers you a choice of formats in which to export the current image.
Resolution allows you to define the resolution at which the image is to be saved to disc.
Orientation allows you to define the orientation at which the image is to be saved to disc.
24 bit sprite allows you to save the currently selected image as a 24 bit sprite. 24 bit sprites give professional quality output on an appropriate printer (or other output device); This output is the best you can get.
- Scale view displays the Scale view control panel which allows you to specify the scale of the image view. You can choose from the six pre-defined scale options or type in your preferred scale. You can click on the arrowheads to make fine adjustments to the scale.
Saving images to disc
It's worth bearing in mind that these images can use up an awful lot of storage space on your hard disc. If you're going to store PhotoView images, consider converting them to JPEG format using ChangeFSI. See page 341.
Quitting PhotoView
To quit PhotoView, press Menu over the PhotoView icon on the icon, bar and choose Quit.
Troubleshooting
You may encounter loading and display difficulties if you do not have enough free memory for the display. You need, for example, a colour card with 24MB of free memory to display an image at 16 base (the highest resolution) and 24-bit colour.
Warning messages are displayed when insufficient memory is available, and PhotoView will adjust the screen display accordingly:
- If you are loading a contact sheet, PhotoView will display as many thumbnails as it is able. Those images which could not be displayed are marked N/A.
- If you are attempting to display an image, PhotoView will offer you a scrolling partial image.
If you are warned that you are short of memory, it's best to quit PhotoView and then quit further running applications in order to free up more memory, before restarting PhotoView.
You may sometimes find that the contact sheet for your Photo CD is displayed, but when you try to display a picture in more detail you get an error from PhotoView 'Cannot allocate needed memory'.
To view an image from a PhotoCD in such circumstances, convert it to a JPEG image, then view or print the JPEG using !Draw.
To do this, first double-click on !PhotoView to load it, then quit !PhotoView - this leaves the PhotoCD module loaded. Next load ChangeFSI, and set it to JPEG Output, Colour. Open a directory display for your inserted PhotoCD, and drag the file corresponding to the image you want to see from the directory $.PHOTO_CD.IMAGES to ChangeFSI. Next save the JPEG image from ChangeFSI to your disc, quit ChangeFSI, and load Draw. To view the image in 32 thousand colours, switch to such a screen mode, then drag the JPEG file from disc to the Draw icon bar icon. The Draw document created may need switching to Misc/Paper limits/Landscape to see the whole image.
RISC OS 3.7 User Guide - 22 JAN 1997