JPEG vs. PNG vs. WebP: Choosing the Right Format
A technical overview of image encoding, transparency support, and why JPEG quality settings do not apply to PNG.
1. JPEG (Joint Photographic Experts Group)
JPEG (.jpg / .jpeg) is the global standard for photographs and natural images.
- How it works: JPEG uses lossy discrete cosine transform compression, discarding high-frequency color variations that the human eye cannot perceive.
- Transparency: JPEG does not support transparency. Any transparent pixels in your source image must be composited onto a solid background color (typically White or Black).
- Best for: Passport photos, profile portraits, camera pictures, and any portal requiring small KB sizes.
2. PNG (Portable Network Graphics)
PNG (.png) is a lossless format based on the DEFLATE compression algorithm.
- How it works: PNG preserves 100% of pixel data without any compression loss. Because of this, standard browser Canvas APIs cannot compress PNG using a variable quality factor (such as 0.8 or 0.5).
- Transparency: PNG supports full 8-bit alpha channel transparency, making it the preferred choice for signatures, logos, stamps, and icons.
- Size trade-off: Because it is lossless, a detailed photo saved as PNG will be 3× to 5× larger than a JPEG at the same resolution. If you have a strict 20 KB limit on a photo, PNG will likely fail.
3. WebP (Web Picture Format)
Developed by Google, WebP (.webp) combines the best features of JPEG and PNG.
- How it works: WebP supports both lossy and lossless compression with modern predictive coding.
- Transparency: WebP supports alpha channel transparency in both lossy and lossless modes! You can have a transparent background while still compressing under strict KB targets.
- Efficiency: WebP files are typically 25% to 35% smaller than comparable JPEGs at equivalent visual quality.
Managing Background Fills in ApplyReady
When you upload a PNG with a transparent background and select JPEG output, ApplyReady provides an explicit Background Fill choice (White or Black). This prevents unwanted black rectangles from appearing behind your transparent signatures or documents when converted to JPEG.