Android ScriptIntrinsicBlur doesn’t blur the whole image and generates a transparent Edge

Android ScriptIntrinsicBlur: Transparent Edge Issue

The Android ScriptIntrinsicBlur class is a powerful tool for applying blur effects to images. However, a common issue encountered is the appearance of a transparent edge around the blurred area. This article delves into the reasons behind this problem and provides solutions to address it.

Understanding the Issue

The transparent edge problem arises due to the nature of the blur algorithm used in ScriptIntrinsicBlur. It operates on a rectangular region of the image, and the blurring process often extends beyond the designated area.

Why Does it Happen?

• Blur Radius: The larger the blur radius, the more pronounced the edge transparency becomes. This is because the blurring extends further into neighboring areas.
• Image Dimensions: Images with irregular aspect ratios or smaller dimensions are more susceptible to edge transparency issues.
• Hardware Acceleration: While hardware acceleration can improve performance, it may sometimes contribute to edge artifacts.

Solutions

There are several approaches to mitigate the transparent edge issue:

1. Padding the Image

Adding padding around the image before blurring can effectively prevent the transparent edge from appearing. This padding should be at least as large as the blur radius.

Code Example:

// Create a Bitmap with padding
Bitmap paddedBitmap = Bitmap.createBitmap(originalBitmap.getWidth() + 2 * blurRadius,
                                       originalBitmap.getHeight() + 2 * blurRadius,
                                       originalBitmap.getConfig());
Canvas canvas = new Canvas(paddedBitmap);
canvas.drawColor(Color.TRANSPARENT); // Set padding background to transparent
canvas.drawBitmap(originalBitmap, blurRadius, blurRadius, null);

// Apply blur using ScriptIntrinsicBlur
// ...

// Crop the padded bitmap to remove excess padding
Bitmap blurredBitmap = Bitmap.createBitmap(paddedBitmap, blurRadius, blurRadius,
                                        originalBitmap.getWidth(), originalBitmap.getHeight());

2. Using a Larger Blur Radius

Surprisingly, using a slightly larger blur radius can sometimes compensate for the edge transparency. This works by extending the blur further, making the transparent edge less noticeable.

3. Combining Blur with Other Effects

Combining blur with other image effects, such as overlaying a background or using a mask, can help disguise the transparent edge.

4. Using Alternative Libraries

If you’re struggling with ScriptIntrinsicBlur’s edge issues, consider exploring alternative blur libraries. Some popular options include:

• RenderScript: Provides more control over the blur process but can be more complex.
• GPUImage: A powerful image processing library that offers a variety of blurring options.

Comparison Table

Conclusion

The transparent edge issue with Android ScriptIntrinsicBlur is a known problem, but there are practical solutions available. Choose the method that best fits your needs based on the level of control required and the desired visual outcome. By understanding the root cause and applying appropriate techniques, you can achieve smooth, high-quality blur effects without unwanted edge artifacts.