#GIMP GRADIENT MAGNITUDE PLUS#

#GIMP GRADIENT MAGNITUDE PLUS#

Here’s the dynamic part, we define the pixel’s energy to be it’s gradient magnitude plus the lowest energy value of the neighboring pixels in the row above (i.e. We start with the top row, where each pixel’s energy is simply it’s gradient value. To do this we can use dynamic programing. how much energy does that pixel contain). Now that we have calculated how much the image is changing at every point, we need to go one step further and figure out the cost of removing that pixel and all the ones before it (i.e. So with this option we convolve the Sobel kernel with our image and again find the gradient magnitude. We can do something called a convolution, which has the same flavor of our subtraction process before (summing up differences), but now it’s just written as a single operation. Lily’s second grade math class, we’ll use a more clever method. Since subtraction is really best left to Mrs. What’s this option? Instead of just considering the change in the horizontal and vertical directions, we can incorporate the change in intensities along the diagonal by using this setting. If you notice in the Carver app, I actually give you the option to use something called the “Sobel” operator. This is the magnitude of the gradient vector for you math geeks. Since we don’t want to consider these derivatives individually we square them, add them together and take the square root of that mess.

In this case, we subtract neighboring pixel values left to right for dx and top to bottom for dy.

Okay better – what’s a derivative? It’s just a fancy word for subtraction. Ahhhh, derivatives!!! Before, you delete your entire photostream due to flashbacks of high school calculus, we just need to step back and take a breath. What’s the image gradient? It’s the derivative of the image. We can do this by finding the gradient of the image. Essentially these are edges in the image and areas that our path will want to avoid. The first thing that we need to figure out is where the image intensity changes. For more information check out this piece by Charles Poynton. These values are used since humans don’t perceive each channel equally and using this weighting produces a more “dynamic” image. The standard way to grayscale an image is to average the red, green, and blue channels with a special weightings. This step isn’t strictly necessary, but makes the following steps simpler and more easily computable.

Once that path is found we can either remove it to make the image smaller or duplicate it to expand the image. The idea behind it is to figure out the least disruptive path through image. The algorithm is quite simple and can be easily understood at an intuitive level. The lowest energy horizontal seam computed using a Sobel Operator. Now improved versions of this algorithm are available in most major image editing programs such as Adobe Photoshop and Gimp. They published this method in ACM in 2007, calling it “seam-carving”. Nearly ten years, two researchers at Mitsubishi came up with a novel algorithm for resizing images while being careful to preserve areas of detail.

Gimp gradient magnitude