This little unit offers the functionality to create a screen shot of the current screen. The screen shot is created as a compressed PNG file with either 256 colors or with 16 gray scales. Of course using the gray scale mode looks not as good, but the resulting image file size is usually smaller.

The screen shot is taken in true color and then reduced to either 256 colors or to 16 gray scales. In order to reduce the image to 256 colors a heavily optimized algorythm is used which makes sure that all important colors are contained in the resulting image. In most cases the resulting image virtually looks exactly like the original true color image. The reduction to gray scales uses Floyd-Steinberg dithering to get a good result.

The function "CreateScreenShotPng" does all the work. It returns a binary string, which you can directly save into a PNG file. You can tell the function to either create a 256 colored or gray scale image. Alternatively you can also tell it to try to keep the image size under a specific threshold. In that case 256 colors are used if the resulting image stays under the specified size limit. Otherwise a gray scale image is returned. The reason for this option is that screen shots of full screen apps often can be reduced that well that there's no difference between 256 colors and gray scales. But when huge bitmaps are contained in the screen shot the colored image takes more space than the gray scale image. By specifying a image file size threshold you can get nice colored images whenever the compression works well and small gray scale images, when colored images would take too much space.

type   TScreenShotType = (st256Colors, st16Grays, st50kb, st100kb, st200kb, st300kb); function CreateScreenShotPng (screenShotType: TScreenShotType) : string;