Image formats
| Term | What it means | When it matters |
|---|---|---|
| JPG / JPEG | A lossy image format designed for photographs. It discards some detail to make files smaller. | Best for photos and portals that only accept JPG. Not ideal for sharp text or transparency. |
| PNG | A lossless image format that supports transparency and sharp edges. | Good for logos, screenshots, and graphics. Usually much larger than JPG for photographs. |
| WebP | A modern format from Google that supports lossy and lossless modes plus transparency. | Often 20–35% smaller than JPG at similar quality, but some older systems reject it. |
| HEIC / HEIF | A container format used by recent iPhones for photos and short videos. | Needs conversion before many websites and Windows apps will accept it. |
| GIF | An older format limited to 256 colors and simple animation. | Fine for small animations, poor for photographs. |
| SVG | A vector format made of shapes and paths rather than pixels. | Scales without blur. Not a photo format and not accepted by most image upload forms. |
Compression and quality
- Lossy compression permanently removes some data to reduce file size. JPG and WebP use it.
- Lossless compression preserves every pixel while encoding the file more efficiently. PNG uses it.
- Quality is an encoder setting, not a universal measurement. A 90% JPG in one encoder may not match 90% in another.
- Target size is the maximum file size you need, such as 100 KB. A tool should reach it without silently producing an unusable image.
- EXIF is metadata stored in many photos: camera model, capture time, orientation, and sometimes GPS coordinates. Re-encoding through a canvas usually removes it.
- DPI (dots per inch) describes intended print density. It does not change the pixel dimensions of a file by itself. A 3×4 cm photo at 300 DPI is about 354 × 472 pixels.
PDF terms
| Term | What it means | When it matters |
|---|---|---|
| A document format that describes pages, text, images, and sometimes forms and links. | The standard for applications, contracts, and scanned documents. | |
| Merge | Combine several PDFs into one document, usually by appending pages in file order. | Useful for joining a cover letter, ID scan, and certificate into one upload. |
| Split | Extract pages or page ranges into separate PDF files. | Useful for sending only the relevant pages of a long report. |
| Rotate | Change the page orientation by 90, 180, or 270 degrees. | Fixes sideways scans without editing the original content. |
| Encrypted PDF | A PDF that requires a password or has restrictions applied. | Most browser tools cannot open it until the password is removed in a PDF reader. |
| OCR | Optical character recognition, which turns an image of text into selectable text. | Not the same as converting to PDF. OCR usually needs a dedicated engine and may require a server for large files. |
Size units
- 1 KB is commonly 1,024 bytes in file-size contexts. Some systems use 1,000 bytes.
- 1 MB is commonly 1,024 KB, or 1,048,576 bytes.
- A portal that says “under 2 MB” may calculate the limit differently. Aim slightly below the stated number.
- File size is not the same as image dimensions. A small file can contain a large pixel canvas, and a large file can contain a small one.