Manipulating PNG Images

Specifying Transparency for PNG Images

One of the advantages of saving images in PNG format is that PNG can have transparent background. Aspose.PSD for .NET provides the feature for specifying transparency for the PNG Images & Raster images as demonstrated in the below section. Aspose.PSD for .NET API can be used to set any color as transparent while creating new PNG images or converting existing images to PNG format. For this purposes, the Aspose.PSD for .NET API has exposed TransparentColor property and PngColorType enumeration that can be set to specify any color to be rendered as transparent in the PNG image. The below provided code snippet demonstrates how to convert an existing PSD image to PNG image by specifying the desired color as transparent.

// For complete examples and data files, please go to https://github.com/aspose-psd/Aspose.PSD-for-.NET

// Load a PSD file as an image and cast it into PsdImage
using (PsdImage psdImage = (PsdImage)Image.Load(dataDir + "sample.psd"))
{

    // specify the PNG image transparency options and save to file.
    psdImage.TransparentColor = Color.White;
    psdImage.HasTransparentColor = true;
    PngOptions opt = new PngOptions();
    psdImage.Save(dataDir + "Specify_Transparency_result.png", new PngOptions());

}

Setting Resolution for PNG Images

Aspose.PSD for .NET exposes the ResolutionSetting class which can be used to set the resolution for all image formats including PNG. This article demonstrates the usage of the Aspose.PSD for .NET API to set the horizontal & vertical resolution parameters for the PNG image format. The code snippet below loads an existing PSD image and converts it to PNG format also changing the resolution.

// For complete examples and data files, please go to https://github.com/aspose-psd/Aspose.PSD-for-.NET

// Load a PSD file as an image and cast it into PsdImage
using (PsdImage psdImage = (PsdImage)Image.Load(dataDir + "sample.psd"))
{
    // Create an instance of PngOptions, Set the horizontal & vertical resolutions and Save the result on disc
    PngOptions options = new PngOptions();
    options.ResolutionSettings = new ResolutionSetting(72, 96);
    psdImage.Save(dataDir + "SettingResolution_output.png", options);
}

Compressing PNG Files

The Portable Network Graphic (PNG) is a lossless compression format for transmitting a bitmap over networks. When you save an image as a PNG file in any program, you may be asked to choose a compression level in a range from 0 to any max level. Setting this value actually compresses the file size and does not decrease the image quality. This article describes how Aspose.PSD APIs allows you to control the PNG file size. Aspose.PSD APIs can be used to set the Compression Levels for the PNG file format using the PngOptions class that has an int type CompressionLevel property. This property accepts a value from 0 to 9 where 9 is the maximum compression. The below provided code snippet demonstrates how to set the Compression Levels using Aspose.PSD for .NET API.

// For complete examples and data files, please go to https://github.com/aspose-psd/Aspose.PSD-for-.NET

// Load a PSD file as an image and cast it into PsdImage
using (PsdImage psdImage = (PsdImage)Image.Load(dataDir + "sample.psd"))
{
    // Loop over possible CompressionLevel range
    for (int i = 0; i <= 9; i++)
    {
        // Create an instance of PngOptions for each resultant PNG, Set CompressionLevel and  Save result on disk
        PngOptions options = new PngOptions();
        options.CompressionLevel = i;
        psdImage.Save(dataDir + i + "_out.png", options);
    }
}

Specifying Bit Depth for PNG Images

Bit depth in imaging is the number of bits used to indicate the color of a single pixel in a bitmap image. Like all other bitmap formats, PNG color depth is also represented in bit such as 1-bit (2 colors), 2-bit (4 colors), 4-bit (16 colors) and 8-bit (256 colors). Aspose.PSD for .NET API can be used to set bit depth for PNG images using BitDepth property exposed by the PngOptions class. At the moment, the BitDepth property can be set to 1, 2, 4 or 8 bits for grayscale and indexed color types. For all other color types only 8 bits are supported. The below provided code snippet demonstrates how to set the Bit Depth for a PNG image.

// For complete examples and data files, please go to https://github.com/aspose-psd/Aspose.PSD-for-.NET

// Load a PSD file as an image and cast it into PsdImage
using (PsdImage psdImage = (PsdImage)Image.Load(dataDir + "sample.psd"))
{
    // Create an instance of PngOptions, Set the desired ColorType, BitDepth according to the specified ColorType and save image
    PngOptions options = new PngOptions();
    options.ColorType = PngColorType.Grayscale;
    options.BitDepth = 1;
    psdImage.Save(dataDir + "SpecifyBitDepth_out.png", options);
}

Applying Filter Methods on PNG Images

Bit depth in imaging is the number of bits used to indicate the color of a single pixel in a bitmap image. Like all other bitmap formats, PNG color depth is also represented in bit such as 1-bit (2 colors), 2-bit (4 colors), 4-bit (16 colors) and 8-bit (256 colors). Aspose.PSD for .NET API can be used to set bit depth for PNG images using BitDepth property exposed by the PngOptions class. At the moment, the BitDepth property can be set to 1, 2, 4 or 8 bits for grayscale and indexed color types. For all other color types only 8 bits are supported. The below provided code snippet demonstrates how to set the Bit Depth for a PNG image.

// For complete examples and data files, please go to https://github.com/aspose-psd/Aspose.PSD-for-.NET

// Load a PSD file as an image and cast it into PsdImage
using (PsdImage psdImage = (PsdImage)Image.Load(dataDir + "sample.psd"))
{
    // Create an instance of PngOptions, Set the PNG filter method and Save changes to the disc
    PngOptions options = new PngOptions();
    options.FilterType = PngFilterType.Paeth;
    psdImage.Save(dataDir + "ApplyFilterMethod_out.png", options);
}

Changing Background Color of a Transparent PNG Image

PNG format images can have transparent background. Aspose.PSD for .NET provides the feature to change the background color of a PNG image that has transparent background. Aspose.PSD for .NET API can be used to set/change color of a transparent PNG image. The below provided code snippet demonstrates how to set/change the background color of a transparent PNG image.

// For complete examples and data files, please go to https://github.com/aspose-psd/Aspose.PSD-for-.NET

// Load a PSD file as an image and cast it into PsdImage
using (PsdImage psdImage = (PsdImage)Image.Load(dataDir + "sample.psd"))
{

    int[] pixels = psdImage.LoadArgb32Pixels(psdImage.Bounds);
    // Iterate through the pixel array and Check the pixel information 
    //that if it is a transparent color pixel and Change the pixel color to white
    int transparent = psdImage.TransparentColor.ToArgb();
    int replacementColor = Color.Yellow.ToArgb();
    for (int i = 0; i < pixels.Length; i++)
    {
        if (pixels[i] == transparent)
        {
            pixels[i] = replacementColor;
        }
    }
    // Replace the pixel array into the image.
    psdImage.SaveArgb32Pixels(psdImage.Bounds, pixels);
    psdImage.Save(dataDir + "ChangeBackground_out.png", new PngOptions());

}