open xml how to set picture size

Neter

3 min read

·

23-11-2024

1

0

Share

Open XML is a powerful format for working with documents, spreadsheets, and presentations. One common task is adjusting the size of images within these files. This article will guide you through different methods for setting picture size in Open XML, focusing on clarity and providing code examples in C#.

Understanding Open XML's Image Handling

In Open XML, images are represented using the <pic> element within a drawing part. The size of the image is controlled through attributes of this element, primarily width and height. These attributes specify the dimensions in EMUs (English Metric Units), a unit of measurement used within the Open XML standard. You'll need to convert pixel dimensions to EMUs for accurate sizing.

Method 1: Setting Picture Size using EMUs Directly

This method is the most direct. You'll specify the desired width and height in EMUs. Remember that 9525 pixels equals 1 inch in EMUs.

// ... other code to load the document ...

// Get the image part
var imagePart = (ImagePart)document.MainDocumentPart.GetPartById("rIdX"); // Replace "rIdX" with the actual relationship ID

// Get the image dimensions (Example using a placeholder for now.  You'll likely load this from the image file itself)
long emuWidth = 952500; //Example: 100 inches
long emuHeight = 952500; //Example: 100 inches

// Find the picture element
var picture = imagePart.FeedData(imagePart.GetStream());


// Set the picture dimensions
var graphicData = picture.Descendants<GraphicData>().FirstOrDefault();
var pictureProperties = graphicData.Descendants<Pic>().FirstOrDefault().Descendants<DocProperties>().FirstOrDefault();

//These attributes are only found if the graphic is a picture. If it's not then you need to get them from elsewhere.
pictureProperties.Attributes<StringValue>().Where(a => a.LocalName == "width").FirstOrDefault().Text = emuWidth.ToString();
pictureProperties.Attributes<StringValue>().Where(a => a.LocalName == "height").FirstOrDefault().Text = emuHeight.ToString();

//Save the changes
document.MainDocumentPart.Document.Save();

Remember to replace "rIdX" with the actual relationship ID of your image part. You can find this ID in the XML structure of your document.

Method 2: Converting Pixels to EMUs

This method is more practical if you're working with pixel dimensions. First, convert pixel values to EMUs, then apply them.

using DocumentFormat.OpenXml.Packaging;
// ...other using statements

// Pixel dimensions of your image
double pixelWidth = 1024;
double pixelHeight = 768;

//Conversion Factor
double EMU_PER_PIXEL = 9525;

//Convert pixels to EMUs
long emuWidth = (long)(pixelWidth * EMU_PER_PIXEL);
long emuHeight = (long)(pixelHeight * EMU_PER_PIXEL);

// ... (rest of the code remains the same as Method 1, using emuWidth and emuHeight) ...

This code snippet shows how to convert pixel dimensions to EMUs before applying them to the width and height attributes. This provides more flexibility when working with images from various sources.

Method 3: Proportional Resizing

Maintaining aspect ratio is important. If you only specify one dimension, the other will be calculated proportionally.

// Set the width, maintaining aspect ratio
long emuWidth = 190500; // Example: 20 inches

// Calculate the height proportionally (assuming original dimensions are known)
double aspectRatio = (double)emuHeight / emuWidth; // from previous calculation.
long newEmuHeight = (long)(emuWidth * aspectRatio);

//Set width and height
pictureProperties.Attributes<StringValue>().Where(a => a.LocalName == "width").FirstOrDefault().Text = emuWidth.ToString();
pictureProperties.Attributes<StringValue>().Where(a => a.LocalName == "height").FirstOrDefault().Text = newEmuHeight.ToString();

// ... (rest of the code remains the same) ...

This example shows how to resize while maintaining the original aspect ratio. This ensures the image doesn't appear distorted.

Error Handling and Considerations

• Relationship ID: Ensure you're using the correct relationship ID for the image part. Incorrect IDs will lead to errors.
• Exception Handling: Wrap your code in try-catch blocks to handle potential exceptions during file access and manipulation.
• Image Format Support: Open XML supports various image formats, but ensure your chosen format is compatible.
• Large Files: Processing large Open XML files can take time. Consider optimizing your code for performance.

By utilizing these methods and best practices, you can effectively manage image sizes within your Open XML documents, ensuring optimal visual presentation and document clarity. Remember to always back up your files before making any significant modifications.