The threshold level is determined by analysing the histogram of the current selection, or of the entire image if there is no selection. Some of the commands ( Erode, Dilate, Open and Close) also work with continuous tone imagesĬonverts grayscale images to black and white and color images to the eight primary colors. These commands assume objects are black and background is white. This submenu contains commands that process binary (black and white) images. Shadows Demo uses all eight kernels to demonstrate the speed of Convolve3x3. Two of the convolution kernels are shown in the illustration. The commands use Convolve3x3, ImageJ's 3x3 convolution function. Median filters a good at removing salt and pepper noise.Ĭommands in this submenu produce a shadow effect, with light appearing to come from a direction corresponding to the command name. This is a time consuming operation because, for each pixel in the selection, the nine pixels in the 3x3 neighborhood must be sorted and the center pixel replaced with the median value (the fifth). It replaces each pixel with the median value in its 3 x 3 neighborhood. Note: this command only works with 8-bit images. The noise is Gaussian (normally) distributed with a mean of zero and standard deviation of 25.Īdds Gaussian noise with a mean of zero and standard deviation of 75.Īdds salt and pepper noise to the image or selection by randomly replacing 2.5% of the pixels with black pixels and 2.5% with white pixels. Use the commands in this submenu to add noise to images or remove it.Īdds random noise to the image or selection. Hold the alt key down to use the standard histogram equalization algorithm. Uses a modified algorithm that takes the square root of the histogram values. Create a selection and the equalization will be based on the histogram of the selection. Uses histogram equalization to enhance image contrast. The final image is produced by combining the two derivatives using the square root of the sum of the squares. Two 3x3 convolution kernels (show below) are used to generate vertical and horizontal derivatives. Uses a Sobel edge detector to highlight sharp changes in intensity in the active image or selection. This filter uses the following weighting factors to replace each pixel with a weighted average of the 3x3 neighborhood. Increases contrast and accentuates detail in the image or selection, but may also accentuate noise. This filter replaces each pixel with the average of its 3x3 neighborhood.
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