# DPlngScan

### The Edit menu

This menu (shown at the right) is the third entry on the main menu. It controls operations altering the physical aspects of the current bitmap.

#### Flip Horiz

This has a similar effect to reflecting the image in a mirror running from top to bottom. The points on the left of the image, move to the right and so on.

#### Flip Vert

Similar to Flip Horiz, but doing the reflection in a horizontal line.

#### Rotate

This allows the bit map to be rotated. Positive angles are anticlockwise. Rotations by 90 and 180 degrees can be done more efficiently, so extra buttons are provided for these. Other angles can be set in the writable icon, either by typing them in directly, or by using the arrows to step through the possible values. Clicking on OK will then carry out the rotation.

When a bit map is rotated by an angle other than 90 or 180 degrees, it will cover a larger area - bit maps must always be rectangular. The new area will be in the current background colour. This can be set from the palette window as described in the colour menu.

#### Shear

This pushes the bit map over sideways. In other words it converts a rectangular shape into a parallelogram. It is possible to shear in either the X or Y direction, by selecting the appropriate button on the dialogue box.

#### Scale

This allows you to change the size of an image. In general there are various ways to do this. Changing the size, is equivalent to changing the resolution of the image. Simply because an image which is twice as wide will have twice as many points - as will one which has the same dimensions but twice the horizontal resolution.

The dialogue box lets you specify the scaling in one of three ways.

- A percentage change - the 'Resize by' option. For example 200 will make the image twice as big, 50 will make it half as big.
- You can specify the new dimensions of the image - 'Resize to'
- You can give the image a new resolution - 'Resample'.

To use any of these options you first need to select the appropriate icon, and then type in the values you desire. Clicking on OK will start the scaling process. The non-writable icons on the right hand side, show the old values for the parameters of the image. The two 'Memory' icons show how much memory the old image used, and how much the new one will. The Lock aspect button will when selected ensure that the image retains the same ratio between the X and Y dimensions.

Although scaling is a common option in bit map programs, usually it is done in a simple way. For example, if you want to make an image twice as tall, the obvious scheme is to just duplicate each row in the image. However a moments thought will show that this is not the best approach. Imagine that two neighbouring pixels have the values 1 and 3, a good guess would be that any pixel inserted between them should have the value 2 i.e. (1+3)/2 or the average. This sort of technique is called 'anti-aliasing'. It can be done in various ways. You can specify the 'filter' to be used from the General configuration dialogue box. The choice of filter will also alter the results of rotation and shear operations. See Choices.

Antialiasing will give better results on images that support a wider range of intensity levels. It may well be better to convert your image to a larger number of bpp (see The Colour menu) before you start processing it.

#### Crop

Crop will allow you to remove unwanted parts of the image around the edge. First you must use the area selection tool (see The main window) to mark out the central area of the image that you wish to keep. Once satisfied, you simply choose Crop from the Edit menu and the outer parts of the image are removed.

#### Extend

There may be the occasion when it is necessary to make the image larger without simply increasing the scale. Extend may be used for this purpose. First you must use the area selection tool (see The main window) to mark out the new extent of the image. It may be first necessary to use the pointer tool to move the image in to the central part of the work area. Once satisfied with the new extent, you simply choose Extend from the edit menu. The added area will be filled with the currently set background colour. (see The Colour menu)

The View menu | Index | The Filter menu

DPlngScan is © David Pilling, 1993
Email:chris@chris-johnson.org.uk