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name="GMT_wxDicom" |
Dr Graham Treece, Department of Engineering
Image sampling and display |
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These controls are all associated with how the current image is interpolated to create the actual displayed image. They can be displayed or hidden by pressing the 'Image sampling and display' button in the control area on the right. The display image updates automatically when any of these controls are changed. |
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These controls are all associated with how the current image is interpolated to create the actual displayed image. They can be accessed from the 'Display' tab in the control area on the right. The display image updates automatically when any of these controls are changed. |
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The operations are always applied in the same order: sub-sampling, then filtering, then zooming and interpolating, then taking the gradient (if required), then thresholding (if required).
- Sub-sampling
- This deliberately sub-samples the original image to a resolution lower by the factor given in this slider. This is mainly useful for demonstrating the effects of interpolation on images.
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- CIE XYZ colour space
- The colour components are a form of normalised red, green and blue.
- CIE L*a*b colour space
- The colour components are lightness, red/green, and yellow/blue.
- CIE L*c*h colour space
- The colour components are lightness, chroma and hue.
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- High-pass or enhance
- Checking this box will display the difference between the filtered output and the original image. Otherwise, the following slider controls the level of enhancement. If this slider is set to zero, the image processing is applied in the normal manner. If it is greater than zero, some of the difference between the initial image and filtered result is added back to the filtered image. When using filters which tend to blur the image, the result is to accentuate small details in the image without changing the background levels.
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- Interpolation
- This controls what interpolation technique is used to form the zoomed display image:
- No interpolation
- Only a single pixel in the display image is set for each pixel in the original image, with everything else left blank. This is good for showing where the actual data is, and also why interpolation is always required.
- Nearest Neighbour
- Display pixels are set to the value of the nearest original pixel, which is an interpolant (it passes through the original data) but with not even C0 (value) continuity. This is useful for revealing the actual size of the original pixels.
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- Cubic Catmull-Rom spline
- Another piecewise spline, which is an interpolant, but only has C1 (gradient) continuity. This tends to emphasise edges a bit more, but can overshoot the data.
- Cubic Mitchell-Netravali spline
- A reasonable balance between the previous two splines.
- Lanczos (sinc) interpolation
- This would represent 'ideal' interpolation if the range was infinite, but here is truncated to the nearest four samples in any direction.
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- Gradient
- Checking this box will display the gradient of the data. If no line is defined (see ), the magnitude of the maximum gradient is shown. If a line is defined, the gradient is calculated and displayed in that direction. Use the 'windowing' (right mouse button) to adjust the contrast.
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- Gradient
- Checking this box will display the gradient of the data. If no line is defined (see general controls), the magnitude of the maximum gradient is shown. If a line is defined, the gradient is calculated and displayed in that direction. Use the 'windowing' (right mouse button) to adjust the contrast.
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- Level
- If this is checked, the slider controls the level at which the image is thresholded. For colour images, each channel is thresholded separately, and they are set to maximum (255) if they are each above the threshold. For greyscale images, data above the threshold is coloured magenta.
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