Understanding Image Formats: JPG vs PNG vs WEBP

Introduction: Why Image Format Matters

When you convert images to PDF, the format of your source images has a direct impact on the quality, file size, and appearance of the final document. Choose the wrong format and you might end up with a PDF that is either unnecessarily large or noticeably blurry. Understanding the differences between common image formats helps you make smarter decisions before you ever hit the "Convert" button.

Each image format was designed with specific use cases in mind. Some prioritize small file sizes at the cost of visual fidelity, while others preserve every pixel perfectly but produce much larger files. In this guide, we will break down the five most common image formats you are likely to encounter — JPG, PNG, WEBP, BMP, and JFIF — and explain exactly when and why you should use each one.

JPEG / JPG

How It Works

JPEG (Joint Photographic Experts Group) uses lossy compression, meaning it permanently discards some image data to achieve smaller file sizes. Under the hood, JPEG relies on the Discrete Cosine Transform (DCT), a mathematical technique that converts blocks of pixels into frequency components. High-frequency details — subtle color shifts and fine textures that the human eye is less sensitive to — are reduced or removed. The result is a file that looks nearly identical to the original at reasonable quality settings but occupies a fraction of the storage space.

Best For

JPEG excels with photographs and complex images that contain smooth gradients, natural lighting, and millions of colors. Portrait photos, landscape shots, product images, and scanned photographs are all ideal candidates for the JPEG format.

Pros

• Small file sizes: A 12-megapixel photograph can be compressed to under 3 MB while retaining excellent visual quality.
• Universal support: Every browser, operating system, image viewer, and PDF tool supports JPEG. It is the most widely compatible image format in existence.
• Adjustable quality: You can control the compression level to balance file size against visual quality.

Cons

• Quality loss on each save: Every time you open, edit, and re-save a JPEG, additional data is discarded. After several rounds of editing, artifacts such as blockiness and color banding become visible.
• No transparency support: JPEG does not support alpha channels, so transparent areas are filled with a solid background color (usually white).
• Poor for text and sharp edges: The lossy compression algorithm tends to blur hard edges, making JPEG a poor choice for screenshots, diagrams, or images with overlaid text.

PNG (Portable Network Graphics)

How It Works

PNG uses lossless compression, which means every single pixel in the original image is preserved exactly. The compression algorithm (based on the DEFLATE method, similar to ZIP files) finds repeating patterns in the image data and represents them more efficiently without throwing anything away. When you decompress a PNG, you get back the exact same pixel data that went in.

Best For

PNG is the ideal choice for screenshots, graphics with text, logos, diagrams, illustrations, and any image where sharp edges and exact color reproduction matter. If your image contains text, line art, or flat areas of solid color, PNG will preserve those details perfectly.

Pros

• No quality loss: You can open, edit, and re-save PNG files as many times as you want without any degradation.
• Transparency support: PNG supports a full alpha channel with 256 levels of transparency, allowing for smooth, anti-aliased edges against any background.
• Excellent for sharp details: Text, icons, and UI elements remain crisp and clear.

Cons

• Larger file sizes for photographs: Because PNG preserves every pixel, a photograph saved as PNG can be 5 to 10 times larger than the same image saved as JPEG. This makes PNG impractical for photo-heavy PDF documents where file size matters.
• No native animation: While APNG exists, it has limited support compared to GIF or WEBP for animated content.

WEBP

How It Works

Developed by Google, WEBP is a modern image format that supports both lossy and lossless compression. In lossy mode, WEBP uses predictive coding (similar to the techniques used in VP8 video compression) to achieve files that are typically 25 to 35 percent smaller than JPEG at equivalent visual quality. In lossless mode, WEBP files are generally 20 to 25 percent smaller than PNG files.

Best For

WEBP is an excellent all-around format for web content, app assets, and any scenario where both quality and file size are important. It effectively replaces both JPEG and PNG in many workflows.

Pros

• Superior compression: Smaller files than both JPEG and PNG at comparable quality levels.
• Transparency support: Unlike JPEG, lossy WEBP images can include an alpha channel for transparency.
• Animation support: WEBP can contain animated sequences, serving as a more efficient alternative to GIF.
• Growing adoption: All major modern browsers (Chrome, Firefox, Safari, Edge) support WEBP.

Cons

• Limited support in older software: Some legacy image editors, document viewers, and operating system preview tools do not recognize WEBP files. If you need maximum compatibility, JPEG or PNG remains safer.
• Less familiar to most users: Many people are unsure how to open or work with WEBP files outside of a browser.

BMP (Bitmap)

How It Works

BMP is one of the oldest image formats still in use. It stores image data in a straightforward, largely uncompressed manner. Each pixel's color value is recorded individually, resulting in a direct, pixel-for-pixel representation of the image. While BMP technically supports basic run-length encoding (RLE) compression, this is rarely used in practice.

Pros

• Perfect quality: Since there is no compression, what you see is exactly what was captured.
• Simple format: BMP files are easy for software to read and write, with no complex decoding required.
• Wide compatibility: Supported natively on Windows and recognized by virtually all image editing software.

Cons

• Very large file sizes: A standard 1920x1080 image at 24-bit color depth produces a BMP file of roughly 6 MB. The same image as a JPEG might be 200 KB. This makes BMP impractical for most modern uses, especially when converting multiple images to a single PDF.
• No transparency: Standard BMP files do not support alpha transparency.
• Outdated: There is rarely a reason to choose BMP over PNG when lossless quality is needed.

JFIF (JPEG File Interchange Format)

How It Works

JFIF is not a separate compression method — it is a specific file format specification for storing JPEG-compressed image data. Think of JPEG as the compression algorithm and JFIF as one of the containers that wraps that compressed data along with metadata such as resolution, aspect ratio, and color space information. The more common .jpg and .jpeg extensions typically use either JFIF or the newer EXIF container format.

When You Encounter JFIF Files

You may come across files with the .jfif extension when downloading images from certain websites or receiving files from older software. Some versions of Windows save images from browsers with the .jfif extension rather than .jpg. Functionally, a .jfif file is identical to a .jpg file in terms of image quality and compression. If your PDF converter does not recognize the .jfif extension, simply renaming the file to .jpg will work in most cases since the underlying data format is the same.

Format Comparison Table

Which Format Should You Use Before Converting to PDF?

The best image format to use depends on what your images contain and what you need from the final PDF document. Here are practical recommendations for the most common scenarios:

For Scanned Documents and Photographs

Use JPEG at 85–95% quality. This provides an excellent balance between visual fidelity and file size. Your PDF will remain compact while looking sharp. If you are scanning archival documents where every detail matters, consider PNG instead.

For Screenshots, Diagrams, and Presentations

Use PNG. The lossless compression ensures that text remains razor-sharp and colors are accurate. The larger file size is worth the quality gain when your images contain text, charts, or UI elements. JPEG compression tends to create visible artifacts around sharp edges and text, which looks unprofessional in a PDF.

For Mixed Content

If your PDF will contain a mix of photographs and graphics, use JPEG for the photos and PNG for the graphics. Most PDF converters, including Image2PDF, handle mixed formats seamlessly and will produce the best results when each image is in its optimal format.

For Minimum File Size

If keeping the PDF as small as possible is your top priority, use WEBP in lossy mode or JPEG. Both formats offer aggressive compression that dramatically reduces file size. WEBP will typically produce slightly smaller files at the same perceptual quality, but JPEG is the safer choice if compatibility is a concern.

Avoid BMP When Possible

Unless you are working with legacy software that only outputs BMP, convert your BMP files to PNG (for lossless quality) or JPEG (for smaller size) before creating your PDF. Including raw BMP images will result in unnecessarily large PDF documents.

Ultimately, the right format comes down to a simple question: does your image need perfect pixel accuracy, or is a small file size more important? For pixel-perfect accuracy, choose PNG. For compact file sizes with great visual quality, choose JPEG or WEBP. And when you are ready to convert, Image2PDF handles all of these formats with no uploads and no sign-ups required.