What is a File Format?

Definition

A file format is the way computer files are stored. To use a simple analogy, just as the same letter can be written in Korean or English, the same information can be stored in various ways. Extensions like '.jpg', '.mp4', and '.pdf' at the end of file names indicate that file's format.

File formats define how data is organized and compressed. For example, the same photo saved in JPG format has a smaller file size but slightly lower quality, while saving in PNG format has a larger file size but perfectly preserves quality. Music files are similar—MP3 has small capacity but compressed sound quality, while WAV has large capacity but original sound intact.

Understanding formats is essential for handling digital content. Using the wrong format can result in files that won't open, unnecessarily large capacity, or degraded quality. Choosing the appropriate format for your situation saves storage space, enables fast sharing, and maintains quality.

Characteristics

• Distinguished by extensions - The 2-4 letters after a dot (.) at the end of file names are extensions. In 'vacation.jpg', '.jpg' is the extension indicating it's an image file. Computers look at this extension to determine which program should open the file.

• Different compression methods - Data compression methods differ by format. 'Lossy compression' discards some information to make files smaller (JPG, MP3). 'Lossless compression' reduces size without discarding any information (PNG, FLAC). 'Uncompressed' formats also exist (BMP, WAV).

• Compatibility is important - Not all programs support all formats. For example, internet browsers display JPG and PNG well, but can't open PSD (Photoshop files). When sharing files with others, it's best to use universal formats they can open.

• Optimal formats differ by purpose - Website images suit JPG or WebP, transparent backgrounds need PNG, vector graphics use SVG, print materials fit TIFF or PDF. Using formats unsuited to the situation causes quality or compatibility issues.

• Convertible but with limitations - Most formats can be converted to other formats. However, converting from lossy compression formats to lossless formats doesn't recover already lost information. Converting JPG to PNG doesn't restore quality lost in JPG.

How to Use

Choosing the right format for each purpose is important. Let's look at different situations.

Image File Formats

JPG/JPEG: The most common image format. Suitable for photos, web images, and social media posts. File size is small and supported by most programs. However, quality slightly decreases each time you save (lossy compression), making it unsuitable for files you'll edit multiple times. Doesn't support transparent backgrounds.

PNG: Suitable for logos, icons, and graphics needing transparent backgrounds. Lossless compression perfectly preserves quality. No quality degradation even with multiple edits. However, for photos, file size is much larger than JPG. Good for screenshots or images containing text.

GIF: Used for short animations or moving images. Color limited to 256 makes it unsuitable for photos, but perfect for simple animations or memes. Nowadays, it's increasingly replaced by more efficient WebP or MP4.

WebP: A modern format developed by Google combining JPG and PNG advantages. File size is about 30% smaller at the same quality. Supports transparent backgrounds and animations. Ideal for website optimization, but may not open in some older programs.

SVG: A vector format used for logos, icons, and illustrations. Has the major advantage of never pixelating when enlarged. File size is also very small. However, can't be used for photos, and complex graphics may have large file sizes.

Video File Formats

MP4: The most universal video format. Plays on almost everything—YouTube, social media, smartphones, TVs. Small file size for the quality makes it good for sharing. In most cases, choosing MP4 is the right choice.

MOV: Apple's QuickTime format. iPhone recordings save in this format. Quality is good but file size is large, and compatibility issues may arise on Windows. Better to convert to MP4 after editing.

AVI: An old format still in use. Can save losslessly making it suitable as original files for editing, but file size is very large. Convert to MP4 for final distribution.

WebM: A web-optimized format used for HTML5 videos. File size is smaller than MP4, but compatibility is lower than MP4.

Music/Audio File Formats

MP3: The most common music format. Plays on almost all devices with small file size. Lossy compression, but most people can't detect quality differences. MP3 is best for general purposes.

WAV: Lossless original sound intact. Used for professional music production, editing, and mastering. However, file size is very large (about 10 times MP3). Convert to MP3 for final distribution.

AAC: More efficient compression than MP3, used in Apple products and YouTube. File size is smaller than MP3 at the same quality.

FLAC: Lossless compression format with WAV quality at about half the size. Preferred by audio enthusiasts, but overkill for general purposes.

Document File Formats

PDF: The standard for document sharing. Appears the same way on any device. Used for print materials, e-books, and official documents. Difficulty editing is both an advantage and disadvantage.

DOCX: Microsoft Word documents. Used when exchanging editable documents. However, layout may differ depending on version or program.

TXT: The most basic text file. No formatting and very small capacity. Suitable for plain text needing no formatting.

Converting Formats

You can use online conversion tools (CloudConvert, Convertio), professional programs (Photoshop, Premiere Pro), or free software (HandBrake, FFMPEG, XnConvert). When converting, always keep originals and remember that converting from lossy to lossless formats doesn't improve quality.

Examples

Example 1: Posting photos on a blog You want to post travel photos on your blog. Original files from the camera are 5MB JPGs. Posting 10 photos at this size makes the page heavy and slow to load. In an image editing program, you reduced resolution and adjusted JPG quality to 80%, reducing each file to 500KB. Visually no difference, but page loading speed is 10 times faster.

Example 2: Creating a logo You created a new YouTube channel logo. Initially saved as JPG, but when placed on the website background, white squares appear around the logo. You realized you need a transparent background and resaved as PNG. Now it looks natural on any background. You also created an SVG version so it won't pixelate when printed large on posters or banners later.

Example 3: Uploading YouTube videos You edited your first YouTube video. Outputting from the editing program in AVI format made a 10-minute video 20GB. With slow internet, uploading would take hours. Re-outputting to MP4 format with H.264 codec reduced file size to 500MB at the same quality. This follows YouTube's recommended upload settings.

Example 4: Managing music files A music producer saves composition work in WAV format. Being lossless, quality is maintained even with repeated mixing and mastering. However, when sending demos to clients, they convert to MP3. File size reduces to 1/10, making it easy to email, and clients can play it on all devices. The final completed version is delivered in both WAV and MP3.

Advantages and Disadvantages

Advantages

• Can optimize for purpose - Choosing the right format for the situation optimizes quality and capacity. For web: small and fast; for editing: quality priority; for sharing: good compatibility. One piece of content can be efficiently used for multiple purposes.

• Efficient storage space usage - Using appropriate compression formats greatly saves storage space. When handling hundreds of photos or multiple videos, format choice significantly impacts hard disk capacity. If using cloud storage, this leads to cost savings.

• Can preserve quality - Using lossless formats during work stages and compression formats only for final distribution minimizes quality degradation. Keeping originals in high quality allows various future uses.

Disadvantages

• Can be confusing - Too many formats exist, making it confusing for beginners to choose. Multiple formats exist even for the same purpose, each with different pros and cons. Wrong choices create the hassle of converting later.

• Compatibility issues arise - Latest formats or professional formats may not open in some programs or devices. When sharing files with others, they sometimes can't open them. Using universal formats is safe, but you may have to give up optimization benefits.

• Quality loss during conversion - Converting to lossy compression formats multiple times progressively worsens quality. For example, repeatedly editing MP4 and resaving as MP4 continuously degrades quality. Therefore, you must plan workflows ahead and minimize unnecessary conversions.

FAQ

Q: I don't know which format to use. A: For the most common situations, choose like this: Photos are JPG, PNG if transparent background needed, videos are MP4, music is MP3, documents are PDF. Knowing just these five covers most situations without problems. If doing more professional work, it's not too late to learn other formats then. Start with highly universal formats.

Q: Should I use JPG or PNG? A: Use JPG for general photos, PNG for logos/icons/graphics needing transparent backgrounds. JPG has small file size but doesn't support transparent backgrounds and quality slightly decreases each save. PNG supports transparent backgrounds and is lossless, but file size is large for photos. Screenshots or images with lots of text are also sharper in PNG.

Q: Does just changing the file extension convert the format? A: No. Just renaming 'photo.jpg' to 'photo.png' corrupts the file so it won't open. To actually convert formats, you must use professional programs or conversion tools. File extensions are just 'name tags' indicating the file's format—changing the name tag doesn't change the contents. Use appropriate conversion programs.

Q: What's the difference between lossless and lossy compression? A: Lossless compression reduces only file size without discarding any information. Decompressing gives you something completely identical to the original (PNG, FLAC, ZIP). Lossy compression makes files smaller by discarding information people don't easily notice (JPG, MP3, MP4). Quality slightly decreases, but in most cases the difference is hard to detect, and file size is much smaller. It's standard to use lossless for working originals and lossy compression for final shared versions.

Q: Does converting formats improve quality? A: No. Converting JPG to PNG doesn't improve image quality; converting MP3 to WAV doesn't improve sound quality. Information already lost through lossy compression can't be recovered. It's like how re-enlarging a copy of a photo doesn't bring back the original's details. Therefore, it's important to save at appropriate quality and format from the start. Always keep originals at highest quality.

Q: Is it safe to use online conversion tools? A: Generally safe but caution is needed. Famous services like CloudConvert and Convertio are trustworthy. However, it's best not to upload personal information or important documents online. Instead, use free programs you install on your computer (XnConvert, HandBrake, etc.). Online tools are convenient but require upload/download time, and large files may have restrictions.

Q: What's a RAW file? Is there a difference from shooting in JPG? A: RAW is a format that stores original data exactly as captured by the camera. JPG is the result after the camera automatically adjusts and compresses. RAW has large file size (3-5 times JPG) but much higher editing freedom. You can adjust exposure, color, white balance, etc. without loss. Professional photographers shoot in RAW and output to JPG after editing. For general users, JPG is sufficient, but for important photos or photos requiring lots of editing, shooting in RAW is better.

Q: Which image format should I use for websites? A: Use JPG for regular photos, PNG or SVG for logos/icons. For sites supporting modern browsers, using WebP can greatly improve loading speed. SVG is vector graphics so it's sharp at any display size and has small file size, making it ideal for logos. For background images or large photos, proper compression and resolution adjustment for web optimization is important. Smaller file sizes mean faster page loading, which benefits user experience and SEO.

Q: Are formats different when editing videos versus final output? A: Yes, using different formats is better. During editing, using high-quality codecs like ProRes (Mac) or DNxHD (Windows) minimizes quality degradation even with multiple edits. However, file size is very large. For final output, using MP4 (H.264 or H.265 codec) has small file size for the quality, facilitating upload and playback. Use a dual strategy: keep originals in high quality, compress for distribution. YouTube recommends MP4 with H.264 codec.