How Can Stack Blur Significantly Speed Up Bitmap Blurring in Android Apps?

Fast Bitmap Blur for Android SDK

The current method of looping through pixels to blur images in Android applications can be time-consuming, particularly for larger images. To address this inefficiency, this article presents a faster algorithm provided by Quasimondo, which employs a combination of box blur and Gaussian blur.

Stack Blur Algorithm

The stack blur algorithm involves creating a moving stack of colors while traversing the image. It continuously adds new color blocks to the stack on the right side and removes leftmost ones. The remaining colors in the stack are adjusted based on their position within the stack. This process results in a visually pleasing blur effect that is significantly faster than a pure Gaussian blur implementation.

Implementation Details

The provided code employs a stack of arrays to store color values and calculates the average color for each pixel based on the stack contents. The algorithm iterates through the input image twice, once horizontally and once vertically, distributing color information across the stack to achieve the blurring effect.

Known Issue and Solution

Some users have encountered an ArrayIndexOutOfBoundsException while using this algorithm. As suggested by @anthonycr in the comments, replacing Math.abs with StrictMath.abs or an alternative implementation of abs has resolved this issue for many.

Benefits

The stack blur algorithm offers the following advantages:

• Significantly faster than looping through individual pixels
• Produces visually pleasing blur effects
• Relatively easy to implement

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