Blurring a digital image

#The present invention relates to a method of processing a digital image.

#As used herein, a digital image comprises an 20 orthogonal array of pixels, i.e. rows of pixels extending in two mutually perpendicular directions over a 2D field and conventionally referred to as horizontal rows and vertical columns of pixels. However, such terminology is used herein for convenience and does not imply any particular orientation of the image.

#In digital image processing a kernel is a subset of a matrix of elements arranged in orthogonal rows and columns. In the matrix each element may have a value of zero or a positive or negative non-zero number. The non-zero matrix elements form the kernel itself. The zero elements take no part in the processing. Conventionally, to process a digital image comprising orthogonal rows and columns of pixels, the kernel is stepped from one pixel to the next along successive rows of the image (actually the image pixels could be processed in any order, but it is easier to conceptualise pixel by pixel processing along successive rows). At each position of the kernel relative to the image each kernel element is notionally aligned with a respective corresponding image pixel; i.e. the kernel defines a set of image pixels having the same shape as the kernel. At each such position of the kernel the value of each image pixel is multiplied by the value of the corresponding element of the kernel, the individual multiplication products are summed, and the sum (if necessary after normalisation) replaces the existing value of the current target pixel. The target pixel is a pixel bearing a fixed relationship to the kernel. In a bi-symmetrical kernel the target pixel is usually the pixel currently corresponding to the centre element of the kernel, but it need not be and may be outside the kernel. See http://williamson-labs.com/convolution-2d.htm. Such processing is known in the art as convolution.

#Embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which:

#FIG. 1 is a block diagram of an image acquisition device.

#FIG. 2 shows a diamond-shaped kernel defined as a subset of a 9×9 matrix.

#FIG. 1 is a block diagram of an image acquisition device 20, which in the present embodiment is a portable digital camera, operating in accordance with certain embodiments. It will be appreciated that many of the processes implemented in the digital camera are implemented in or controlled by software operating on a microprocessor, central processing unit, controller, digital signal processor and/or an application specific integrated circuit, collectively depicted as processor 120. All user interface and control of peripheral components such as buttons and display are controlled by a microcontroller 122.

#In operation, the processor 120, in response to a user input to microcontroller 122 such as half pressing a shutter button (pre-capture mode 32), initiates and controls the digital photographic process. Ambient light exposure is determined using a light sensor 40 in order to automatically determine if a flash is to be used. The distance to the subject is determined using a focusing mechanism 50 which also focuses the image on an image capture device 60. If a flash is to be used, processor 120 causes a flash device 70 to generate a photographic flash in substantial coincidence with the recording of the image by the image capture device 60 upon full depression of the shutter button. The image capture device 60 digitally records the image in colour. The image capture device is known to those familiar with the art and may include a CCD (charge coupled device) or CMOS to facilitate digital recording. The flash may be selectively generated either in response to the light sensor 40 or a manual input 72 from the user of the camera. The high resolution image recorded by the image capture device 60 is stored in an image store 80 which may comprise computer memory such a dynamic random access memory or a non-volatile memory. The camera is equipped with a display 100, such as an LCD, both for displaying preview images and displaying a user interface for camera control software. Typically displays such as the display 100 are touch screen displays readily enabling user interaction with applications running on the image acquisition device 20.

#In the case of preview images which are generated in the pre-capture mode 32 with the shutter button half-pressed, the display 100 can assist the user in composing the image, as well as being used to determine focusing and exposure. Temporary storage 82 is used to store one or plurality of the stream of preview images and can be part of the image store 80 or a separate component. The preview image is usually generated by the image capture device 60. For speed and memory efficiency reasons, preview images may have a lower pixel resolution than the main image taken when the shutter button is fully depressed, and can be generated by sub-sampling a raw captured image using software 124 which can be part of the general processor 120 or dedicated hardware or combination thereof.