JPG, PNG, and images to PDF: choose a format based on the content
The best image format is not the one with the most familiar extension. It is the one that preserves the details your image needs while keeping file size and compatibility appropriate for its destination.
JPG versus PNG
JPG and PNG can display the same rectangular image, but they encode it differently. JPG is designed around lossy compression: it removes visual information in ways that are often difficult to notice in photographs. PNG uses lossless compression, preserving the exact decoded pixel values and supporting transparency.
| Characteristic | JPG | PNG |
|---|---|---|
| Best for | Photographs, scans, gradients, natural textures | Logos, diagrams, text, screenshots, transparency |
| Compression | Lossy; smaller files are possible | Lossless; repeated saving does not add compression artifacts |
| Transparency | Not supported | Supported with an alpha channel |
| Typical weakness | Artifacts around sharp edges and text | Large files for detailed photographs |
Use JPG for continuous-tone images
A photograph contains gradual changes in color and brightness. JPG compression handles that material efficiently, often creating a much smaller file than PNG. It is a practical choice for camera photos, scanned receipts, product images without transparent backgrounds, and images intended for email or web publishing.
Lossy compression is cumulative. Opening a JPG, editing it, and saving it as JPG again can introduce another generation of artifacts. Keep a high-quality original when the image will be edited repeatedly. Convert a finished copy for distribution rather than using the converted file as the only master.
Use PNG for sharp boundaries and exact pixels
PNG is usually the stronger choice for interface screenshots, charts, icons, diagrams, and images containing small text. Sharp one-pixel lines and flat color regions remain clean. PNG is also appropriate when a logo or product cutout must be placed over different backgrounds.
Converting a JPG to PNG does not restore detail already discarded by JPG compression. The new PNG stops additional lossy encoding, but block artifacts, ringing, and blurred edges from the source remain visible. Format conversion cannot recreate information that is no longer present.
What happens to transparency
PNG can store an alpha value for each pixel, allowing fully transparent and partially transparent areas. JPG stores only color values. When Converttwo converts PNG to JPG, it first fills the canvas with white and then draws the PNG over it. Transparent areas therefore become white in the finished JPG.
This behavior is predictable, but it may not suit every design. A white logo intended for a dark background can disappear when flattened onto white. Before converting, preview the transparent image against white. If the result needs a different background, add that background in an image editor before creating the JPG.
A transparent pixel reveals whatever is behind the image. A white pixel always displays white. Once transparency is flattened into JPG, changing the background requires editing or masking the image again.
Resolution, dimensions, and perceived quality
Pixel dimensions describe how much image information is available. A 3000 × 2000 image contains six million pixels regardless of whether it is saved as JPG or PNG. Changing the format alone does not increase those dimensions. It changes how the existing pixels are encoded.
For screens, the required dimensions depend on the space where the image will appear. A thumbnail does not need camera-sized dimensions. For print, physical size and pixel density work together. A 2400-pixel-wide image printed at 300 pixels per inch is about eight inches wide before resampling.
Why enlarging does not create real detail
Upscaling asks software to invent new pixels between existing ones. It can smooth jagged edges but cannot reveal genuine letters, facial details, or texture that the source never captured. If small text is unreadable in the original scan, changing PNG to JPG or placing it in a PDF will not make it legible.
Browser dimension limits
Extremely large images can exceed browser canvas or memory limits. Converttwo rejects an image when either dimension is greater than 16,384 pixels. A file can also be difficult to process when its compressed size looks modest but its decoded pixel area is enormous. Resize unusually large panoramas or scans before conversion.
Preparing images for an A4 PDF
The Images-to-PDF tool accepts JPG, PNG, and WebP files and creates one portrait A4 page per image. Each image is placed with a 10 mm margin and scaled down proportionally when necessary. Smaller images are not enlarged beyond their original pixel dimensions. This avoids forced upscaling but can leave extra white space around a small source.
Order images by filename
Natural filename order becomes the page order. Rename files with numeric prefixes such as 01-cover.jpg, 02-receipt.jpg, and 03-signature.png, then confirm the selected-file list before converting. Check that portrait images are already rotated correctly; the output pages remain portrait even when a wide image is placed on them.
Prepare scans consistently
A document assembled from phone photos looks more professional when every page has similar cropping, brightness, and perspective. Straighten tilted pages, remove unnecessary desk background, and use the same orientation before combining them. If readable text is the goal, avoid aggressive JPG compression and inspect the smallest characters at 100% zoom.
Understand what an image PDF can and cannot do
An image-based PDF is useful for sharing a set of scans in one file. The visible words are pixels unless OCR has been applied separately, so they might not be searchable, selectable, or accessible to screen readers. For records that need text search or accessibility, use an OCR workflow and review the recognized text.
A reliable conversion and review workflow
- Keep the highest-quality original available.
- Choose JPG for photographic content or PNG for sharp graphics and transparency.
- Preview transparency against the background that JPG conversion will use.
- Check dimensions and rotate or crop images before combining them into PDF.
- Select the converter and verify every listed filename.
- Download the result with a distinct name rather than overwriting the original.
- Inspect at 100% zoom and test the file in its intended destination.
Common questions and mistakes
Why is my PNG larger than the JPG?
Lossless PNG must preserve the decoded pixel values, while JPG can discard subtle information. For a photograph, that difference can be dramatic. For a simple logo with few colors, PNG may still be compact.
Why did the converted image keep the same width and height?
The JPG-to-PNG and PNG-to-JPG tools preserve source pixel dimensions. They change encoding, not geometry. Use an image-resizing tool when the goal is a new width or height.
Why is text blurry after PNG-to-JPG conversion?
JPG compression groups visual information and is less effective around high-contrast edges. Small dark text on a light background exposes those artifacts. Keep text-heavy graphics as PNG when file size permits.
Why does the PDF show margins?
Images are fitted within an A4 page with a 10 mm margin. This prevents content from touching the page edge and keeps the full image visible. It is not a border added to the original image file.
Choose the format, then convert
Start with the content type: photographs usually favor JPG, while sharp graphics and transparency favor PNG.
Open the Images to PDF tool