Scaling Monochrome Images

ImageMan has full support for antialiased scaling of black and white images, what is commonly referred to as scale-to-gray. Antialiasing can only be used when shrinking a monochrome image, but it produces stunningly superior results.

The trick to antialiasing is to use shades of gray in the new, smaller image to represent a given area from the original image. Of course, you can't have shades of gray in a monochrome image there's only black or white so ImageMan actually creates a 16-color or 256-color image to represent the scaled version of the original monochrome image.

To use antialiasing when shrinking a monochrome image, simply pass the COPY_ANTIALIAS (for a 16-color resulting image) or COPY_ANTIALIAS256 flag (for a 256-color resulting image) to the ImgCopy function. In general, 16 levels of gray is adequate for most images, so you should use the COPY_ANTIALIAS flag unless you have a specific need for a 256-color result.

Here's an example of scaling an image using both methods:

// In this example, the source image must be larger than

// the destination, which will be 100 x 100 pixels.

//

// Create a 16-level grayscale image

hImage2 = ImgCopy(hImage, 100, 100, NULL, COPY_ANTIALIAS)

//

// Create a 256-level grayscale image

hImage2 = ImgCopy(hImage, 100, 100, NULL, COPY_ANTIALIAS256)