GB2359232A - A computer graphics icon that provides a reference for the effects applied to an image - Google Patents

Abstract

A new design of digitally generated graphic is presented which is intended to help maintain the frame of reference when viewing digitally processed images. The intention is that the Digital Frame of Reference (DFOR) be included with all digitally processed images and processed using the same factors as were used on the image. An unprocessed DFOR can then be displayed adjacent to the processed DFOR in order to reintroduce a frame of reference and clearly illustrate 'what has happened to the image'. This would allow the viewer to perceive any artefacts that may have been introduced into the image by the processing. This is particularly important where the image requires interpretation by the viewer as in, for example, forensics and medical diagnosis. This paper presents a grey scale version of the DFOR that is suitable for applications such as medical imaging. The DFOR includes grey scale from 0 to the max bit depth in 0,30,70 90% steps on a 50% background, the full frequency range from 0 to the Nyquist frequency, high, medium and low contrast boundaries and linear/curvilinear features. The same method could be extended to any other digital image system and could be easily modified to include colour.

Description

1 k Digital Frame of Reference for Viewing Digital hnages.

2359232 Introduction:

Digital imaging systems allow the image acquisition and display to be separated. This allows virtually unlimited post processing of the image data. Therefore in viewing a digital image there is a danger that the traditional frame of reference associated with film images will be used even when the image presented is in fact a 'pseudo' image. This could be a major concern with images that. require analysis or interpretation such as in forensics and medical imaging.

In digital medical imaging, image processing is widely used in order to enhance image presentation. This can range from simple sharpening up to complex non-linear algorithms'. By definition all image processing will introduce artefacts, some intentional, some not. An example of this is the commonly used 'unsharp mask' alorithin' that may introduce a ringing artefact at boundaries. If the viewers' frame of reference is not adjusted to allow for these artefacts they may be wrongly interpreted as genuine clinical features. A miss diagnosis may become even more likely with the increasing use of more complex algorithms where the artefacts are not as obvious.

It is therefore suggested that each digital image will require its own 'reference point' in order to communicate to the clinician 'what has happened to the image'. There appears to be three options to achieve this, 1) always have the raw image presented 2) state the algorithms used and train the staff to understand the potential artefacts or 3) present each image with graphical information that relates the processes applied to that image.

The aim of this paper is to present a new graphical icon optimised for grey scale medical imaging. The icon is imbedded in the digital image and processed in the same way as the image. This icon will graphically present information relating to the impact of any image processing on the original image data and can be readily compared to the unprocessed icon reintroducing a frame of reference.

Method The Digital Frame of Reference (DFOR) was generated using commercial graphics packages provided by the Corel Graphics suite v8.0. (Corel Corporation, Canada) The presented DFOR includes the following elements:

Full grey scale range from 0 to max bit depth in 0,30,70 90% steps on a 50% background Full frequency range from 0 to Nyquist frequency.

High, medium and low contrast boundaries Linear and curvilinear features.

Suggested dimensions of the DFOR image are shown in figure 1. The circular detail is initially presented on a large area square background (X by X) to allow for edge effects in processing. All dimensions are related to this initial square allowing easy reproduction and scaling. The ellipse has a grey level of 50% and ratio of 2: 1. It is offset 0. 0005X from the edge of the circle. It is intended that the value X would be approximately 20% of the image size. The final image can be cropped by a circle OAX in radius (figure 2a) before or after processing. This is optional but has been applied post processing to all the images presented for clarity. Another option is to add a noise component and figure 2b shows 5% Gaussian noise applied to an inner circle.

Results The DFOR has been processed with several simple algorithms to illustrate its sensitivity. These are shown in figures 3a-c.

It can be seen that the presentation of the processed DFOR clearly illustrates the artefacts introduced by the processing. A chest x-ray is shown in figure 4a. This shows a normal chest x-ray which when processed starts to exhibit the appearance of a chest with increased lung niarkings, a J-, Q potential sign of disease. The DFOR shown with the processed image shows the high level of applied processing.

Conclusion and discussion

Digital imaging systems have many advantages over conventional film systems. One of these is the ability to process the images to enhance the presentation of certain features. This is routinely done on most digital acquisition systems to enhance the image presentation. However little is done to communicate to the viewer how the original data has been manipulated and in particular the artefacts that may be introduced. The presented graphical icon has been designed to communicate to the viewer 'what has happened to the image'. The design is easy to digitally generate and presents signals that cover the full range of the system. It is intended that this icon would be imbedded into the image and processed with the same parameters as the image. This could then be presented sideby-side with an unprocessed DFOR allowing the viewer to acquire a new frame of reference for the image.

This design can be used in any digital imaging modality and can be readily modified for specific applications, e.g. for colour and specific contrastlfrequency ranges. The main advantages of this method of communicating the processes applied to an image, over the other possible methods, are that it is scalable, visual, unambiguous, easy to reproduce and takes up relatively little image space. Combining the DFOR with other technologies, such as image watermarking', would help to provide secure, easily interpretable and ultimately reliable images for all disciplines requiring a high level of image probity.

References 1 Clarke LP. Kallergi M. Qian W. Li HD. Clark RA. Silbiger ML. Tree- structured non-linear filter and wavelet transform for microcalcification segmentation in digital mammography. Cancer Letters. 77(2-3):173-81,1994.

Prokop M. Schaefer CM. Oestmann JW. Galanski M. Improved parameters for unsharp mask filtering of digital chest radiographs. Radiology. 187(2):521-6, 1993.

Chang DC. Wu WR. Image contrast enhancement based on a histogram transformation of local standard deviation. YEE Transactions on Medical Imaging. 17(4):518-31, 1998.

4. Prokop M. Schaefer-Prokop CM. Digital image processing. European Radiology. 7 Suppl 3:S73-82, 1997.

5. Zliao J. Watermarking by Numbers. Nature, 384(6609):514, 1996.

1 3 1. A graphic containing elements that are sensitive to processes that affect resolution, contrast, colour or noise in an image to facillitate interpretation of any applied processes.

2. A graphic as claimed in claim 1 that is imbedded in a digital image.

3. A graphic as claimed in claim 1 that is processed independently.

4. A graphic as claimed in claim 2 or claim 3 that is presented alongside an unprocessed version of its self for easy interpretation.

5. A graphic substantially as herein claimed and illdstrated in the accompanying drawings.

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Amendments to the claims have been filed as follows 1. A computer graphics icon containing elements that are sensitive to changes in resolution, contrast, colour or noise to allow interpretation of processes applied to an image to which it is linked.

2. A graphic as claimed in claim 1 that is imbedded in a digital image.

3. A graphic as claimed in claim 1 that is processed independently.

4. A graphic as claimed in claim 2 or claim 3 that is presented alongside an unprocessed version of its self for easy interpretation.

5. A graphic substantially as herein claimed and illustrated in the accompanying drawings.