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 convert anything.

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. This article covers five formats (JPG, PNG, WEBP, BMP and JFIF): how each one is compressed, what it suits, and what Image2PDF does with it.

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 several times larger than the same image saved as JPEG. This makes PNG impractical for photo-heavy PDF documents where file size matters.
• No animation in standard PNG: The animated variant, APNG, plays in modern browsers but is supported by fewer editors and apps than GIF.

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 (the technique used in VP8 video compression). Google reports that lossy WEBP files are 25 to 34 percent smaller than comparable JPEGs, and lossless WEBP files about 26 percent smaller than PNGs.

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.
• Re-encoded when converted to PDF: A PDF cannot store WEBP data, so a converter has to decode the image and save it again in a format PDF supports. Image2PDF re-encodes WEBP as JPEG at quality 0.92 and turns transparent areas white, so the size advantage of WEBP does not carry over into the PDF.

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 to store and send.
• 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.
• Not kept as-is in a PDF: Like WEBP, BMP data cannot go into a PDF unchanged. Image2PDF re-encodes BMP images as JPEG at quality 0.92, so the PDF is much smaller than the BMP files, but the pages are no longer lossless.

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. Image2PDF accepts .jfif files directly and handles them exactly like .jpg files.

Format Comparison Table

What Image2PDF Does With Each Format

A PDF can hold JPEG data unchanged, and it can hold lossless image data such as the pixels of a PNG. Other formats have to be converted first. Image2PDF identifies each file's real format from its first bytes, not from its extension, and then:

• JPG / JPEG / JFIF: embeds the file byte-for-byte, with no re-compression. The exception is a photo carrying an EXIF orientation tag other than "normal" (common for phone photos): it is rotated upright and re-encoded as JPEG at quality 0.92 so the page is not sideways.
• PNG: stores the pixels without lossy compression and keeps transparency. The pixels are re-compressed, so the size in the PDF can differ from the original PNG file.
• WEBP and BMP: decodes the image, draws it on a white background (transparent areas become white) and re-encodes it as JPEG at quality 0.92.
• HEIC/HEIF (the iPhone's default photo format) is not supported, because most browsers cannot decode it. You get a message asking you to convert the photo to JPG or PNG first. Other formats, such as GIF, TIFF and SVG, are also rejected with a message.

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. Image2PDF accepts mixed formats in one batch, so each image can stay in the format that suits it.

For Minimum File Size

If keeping the PDF as small as possible is your top priority, use JPEG. Image2PDF embeds JPG files unchanged, so each page is about the size of the original file (phone photos that need rotating upright are the exception and are re-encoded at quality 0.92). WEBP does not help here: its smaller files are re-encoded as JPEG at quality 0.92, and the resulting page can be larger than the WEBP you started with. PNG pages stay lossless, which makes them large for photographs. To shrink a PDF further, reduce the pixel dimensions or the JPEG quality of your images before converting.

For BMP Files

Image2PDF accepts BMP files but re-encodes them as JPEG at quality 0.92, so the PDF will not contain the raw BMP data and will not be lossless. That is fine for photos. If a BMP contains small text or sharp graphics that must stay pixel-exact, convert it to PNG first; PNG is embedded losslessly.

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 the smallest PDF from Image2PDF, choose JPEG. When you are ready to convert, Image2PDF handles JPG, JFIF, PNG, WEBP and BMP in your browser, with no uploads and no sign-ups required.