addOpacity()

Adjusts the opacity/transparency of an image. Output is always PNG to preserve transparency.

Signature

public function addOpacity(
    string $inputImagePath,
    string $outputImagePath,
    int $opacityPercent
): void

Parameters

`$inputImagePath` (string, required)

Path to the input image file. Supports JPEG, PNG, and GIF.

`$outputImagePath` (string, required)

Path where the output PNG will be saved. Always outputs PNG format.

`$opacityPercent` (int, required)

Opacity level (0-100).

0 - Fully transparent (invisible)
50 - Semi-transparent
100 - Fully opaque (no transparency)

Values outside 0-100 are automatically clamped.

Return Value

Returns void. Creates the output PNG file.

Behavior

Opacity Calculation

The method applies the opacity to all pixels in the image:

Creates a transparent canvas
Copies the original image with specified opacity
Saves as PNG to preserve transparency

Output Format

Always outputs PNG, regardless of input format:

JPEG → PNG
PNG → PNG
GIF → PNG

Examples

Basic Usage

use Kenura\Imagick\ImageProcessor;

$processor = new ImageProcessor();

// Make image 50% transparent
$processor->addOpacity('image.jpg', 'transparent.png', 50);

Create Watermark

// Create semi-transparent logo for watermarking
$processor->addOpacity('logo.png', 'watermark.png', 40);

// Use as watermark
$processor->addWatermark(
    'photo.jpg',
    'watermarked.jpg',
    'watermark.png',
    'bottom-right',
    10
);

Different Opacity Levels

// Very transparent
$processor->addOpacity('image.jpg', 'very-transparent.png', 20);

// Semi-transparent
$processor->addOpacity('image.jpg', 'semi-transparent.png', 50);

// Slightly transparent
$processor->addOpacity('image.jpg', 'slightly-transparent.png', 80);

// Fully opaque (no change)
$processor->addOpacity('image.jpg', 'opaque.png', 100);

Batch Processing

$images = glob('images/*.jpg');

foreach ($images as $image) {
    $filename = pathinfo($image, PATHINFO_FILENAME);
    $processor->addOpacity($image, "transparent/{$filename}.png", 60);
}

Opacity Scale

Value	Description	Use Case
0-20	Very transparent	Ghost effects, subtle overlays
20-40	Mostly transparent	Watermarks, background patterns
40-60	Semi-transparent	Overlays, fade effects
60-80	Slightly transparent	Subtle effects
80-100	Nearly/fully opaque	Minimal transparency

Best Practices

1. Use PNG Extension

// ✅ Good: Clear that output is PNG
$processor->addOpacity('image.jpg', 'output.png', 50);

// ⚠️ Confusing: Output is still PNG despite .jpg extension
$processor->addOpacity('image.jpg', 'output.jpg', 50);

2. Validate Opacity Range

// Values are automatically clamped, but validate for clarity
$opacity = max(0, min(100, $userInput));

$processor->addOpacity('image.jpg', 'output.png', $opacity);

3. Consider File Size

// PNG files can be larger than JPEG
// Original JPEG: 500KB
$processor->addOpacity('photo.jpg', 'transparent.png', 50);
// Output PNG might be: 800KB+

Common Use Cases

1. Watermark Creation

// Create transparent watermark
$processor->addOpacity('logo.png', 'watermark.png', 50);

2. Overlay Effects

// Create semi-transparent overlay
$processor->addOpacity('texture.jpg', 'overlay.png', 30);

3. Fade Effects

// Create faded version
$processor->addOpacity('image.jpg', 'faded.png', 60);

Common Issues

Issue: Output file is JPEG, not PNG

Cause: You specified .jpg extension

Solution: Output is always PNG. Use .png extension:

// Even with .jpg extension, output is PNG
$processor->addOpacity('input.jpg', 'output.jpg', 50);

// Better: use .png extension
$processor->addOpacity('input.jpg', 'output.png', 50);

Issue: File size increased

Cause: PNG files are often larger than JPEG

Solution: This is expected when converting JPEG to PNG with transparency

Issue: No visible change at 100% opacity

Cause: 100% opacity means fully opaque (no transparency)

Solution: Use lower values for transparency:

// No change
$processor->addOpacity('image.jpg', 'output.png', 100);

// Transparent
$processor->addOpacity('image.jpg', 'output.png', 50);

addWatermark() - Use transparent images as watermarks
resizeImage() - Resize before adjusting opacity