Positive Image - part 2

By Colin Fisher-McAllum

Since I completed part one of the Positive Image review there have been a couple of minor upgrades and one big bonus. PI, now up to v1.12 comes supplied with an 040 version. While there are few 040s currently sitting on Atari user desktops, there are quite a few 030s with FPUs fitted. This 040 version will run on these machines. So to recap, Positive Image now comes in standard 68000, 68030 and the enhanced 68040 versions. All are supplied on the master disks.

An image processing utility needs to have good block handling routines. I have not been disappointed with the way Positive Image handles blocks. From a standard rectangle to irregular shapes they can be defined quite simply. There is even an auto-trace function that will enclose areas of a given shade. Using the tolerance setting correctly it is possible to trace areas of slightly differing shades. The auto-trace, like the manual irregular shape block tool, used a series of bezier curves to enclose the area. Each curve has control points that can be moved to give fine control over the editing of the shape. As would be expected, if the area is very irregular the number of control points is quite high and it can be hard selecting the right one to move. This to one side, the block selection tools are excellent. Having defined a block it can now be cut, copied, manipulated, masked, processed and pasted.

Cuting or coppying will add the block to the Atari clipboard where from where it can be recalled at any time. A block, or full image can be manipulated by rotation, resize, mirror, shearing or even warping. Rotation is in multiples of one degre and the window grows if rotation takes the block out of the image limits. There are two ways to resize an image. Scale, which changes the image in fixed sizes of 12%, 25%, 50%, 200%, 400% and 800% on either the horizontal or vertical. Or the is the more specific resize option where where the width and height are entered in pixel values. Resizing only works on full images and rectangular blocks. Mirror and shearing are exactly what you would expect and both work on the horizontal and vertical plane. There are two types of image warping, the first is based round a central point. This particular option is a hard to go over the top with and therefore gives some interesting and not too distorted results. On the other hand there is Object Warp where there are 4 corner control points. Used carefully this can give excellent perspective or distortion, but it's easy to over do it.

<img SRC="/images/atari-phile/pi_2c.png" ALT="IMAGE" ALIGN="right">The masking options in Positive Image are quite simple - but it's worth reading the manual carefully. A mask can be applied to a whole image, a block or the whole image excluding the defined block. Of course the block can be regular or irregular in shape. The mask does not have to be solid, it can have up to 256 greyscale levels. Applying a gradient mask will allow more of the object through to the image where the grey is light and less where the grey is dark. The object can be a pasted block or colour applied by the painting tools. Masks can be created as 256 greyscale images and saved to disk for future use and PI comes with good selection on the master disk. Simple masks can be created with the gradient option. It takes patience and practice to get the best results from using masks but it's worth taking time to master this very powerful tool.

<img SRC="/images/atari-phile/pi_2.png" ALT="IMAGE" ALIGN="left">Images or blocks can be filtered. This is the process of having an individual pixel effected by the pixels it is adjacent to. Using a grid of 3x3, 5x5 or 7x7 the filter has a set of values that are applied pixel by pixel. Depending on these values the results can be outstanding. Filters such as Smooth, Sharpen and Blur are already defined. The adventurous amongst you will enjoy entering your own values and see what the results will be. There are some
filters supplied that can be loaded from disk, with the likes of Emboss, Relief and Vibrate there are plenty for you to experiment with. Obviously, you can save your own filters. This is a very time intensive process, so be patient. Even using the DSP on a Falcon, some processes are very slow, but give it time as the results can be excellent.

By the way, I haven't mentioned that these processes can be carried out on individual colour channels [Red, Green and Blue]. For example you could load a picture, emboss the red channel, negative the Green and sharpen the Blue!

Having processed your image you may still want to touch it up. I covered the Retouching tools in the last issue, however the pixel tools can now come into their own. Simply adjusting the brightness and/or contrast can turn a good image into a very good image. There is an excellent tool called Stretch Contrast. The manual says, "This is an automatic procedure and requires no user interaction, simply press the button and let PI do the work!" Basically, it creates a histogram in memory and then works out what it thinks would be the optimum contrast level. Even though you have no control over this option, it is often worth letting PI have it's way. You can always go back to your original if you don't like the result!

Finally, and to be honest I don't know why it's here, there is the option to create a Stereogram. OK, it's a bonus. Some people have spent almost half the cost of Positive Image on a program that only creates stereograms, so it must be a useful tool. I have never managed to see anything in any stereogram so there was no point im my creating one. However, for those of you that can see into the mysteries of these pictures the options seem to be manifold.

All in all, Positive Image is a very powerful tool that anyone who needs to process and touch up images [or those who just like to play with images] would be delighted to use. It's main faults are the lack of GIF support [this was covered in part one of this review] and it's speed. Many options do take a long, long time to complete. However, what it does, it does very well indeed and it's worth being patient because the results can be excellent.