Question
Answer and Explanation
Poor print quality in Swift-generated PDF documents can stem from several factors related to how the PDF is created and rendered. Here are some common reasons and solutions:
1. Resolution Issues:
- Problem: If you're rendering images or text at a low resolution, the quality will suffer when printed. PDF's are often used at higher DPI (Dots Per Inch) than what is displayed on a monitor.
- Solution: Ensure that when you create your PDF context, you set an appropriate resolution. When drawing images, make sure the original image resolution is high enough and that you're not scaling down the image too much in the PDF. For example, if creating a graphic context you can use UIGraphicsBeginImageContextWithOptions with a scale factor (e.g. scale of 2.0 for retina-like resolutions) or you can use CGContext with appropriate DPI settings.
2. Font Embedding:
- Problem: If the fonts used in your PDF are not embedded within the document, the PDF viewer might substitute them, leading to discrepancies in appearance. Some substitute fonts might not have same kerning or metrics as the original.
- Solution: Embed the fonts in the PDF. When using Core Graphics, you can pass font data during text drawing. When using attributed strings you can ensure the font attribute has a suitable font object.
3. Image Compression:
- Problem: Compressing images (e.g. using JPEG with low quality) to reduce the PDF size can result in noticeable artifacts and blurry edges when printed.
- Solution: Use lossless compression techniques (such as PNG or lossless JPEG settings), or reduce compression artifacts by avoiding excessive compression of images. Try to ensure source image resolution is sufficient for print DPI before adding to the PDF.
4. Incorrect Color Space:
- Problem: If your graphics are rendered in a color space not suitable for printing (e.g., RGB for an printer optimized for CMYK), color inaccuracies may appear.
- Solution: Convert the color space to CMYK before adding elements to the PDF for printing purposes, if possible.
5. PDF Rendering Engine:
- Problem: The library or method used to create your PDF might have limitations or could be implemented poorly.
- Solution: Experiment with different PDF generating libraries or methods. Apple’s built in libraries like Core Graphics are good starting point, or libraries like PDFKit.
6. Text Rendering Issues:
- Problem: Text may appear jagged or blurry due to incorrect positioning or antialiasing issues within the graphics context.
- Solution: Use functions for text that use sub-pixel positioning for enhanced rendering. Check that the context has the correct text rendering parameters set if required.
7. Incorrect Graphics Scaling:
- Problem: If graphics elements are scaled incorrectly, the lines may render as blurred or pixelated.
- Solution: When creating graphical content, use pixel-perfect positioning where possible. Use scaling transforms at highest possible resolution to minimise information loss.
To fix your situation, you should carefully examine each of these potential issues in your PDF generation code. Review your usage of Core Graphics, PDFKit or any third party libraries you might be using. Start with high resolution assets, embed fonts, use lossless compression for images, use a good rendering engine, and ensure you are using a correct colour space.