Lossless vs Lossy Compression: Everything You Need to Know

The Fundamental Question of Digital Compression

Every digital file you work with — every photo, song, video, and document — is ultimately a sequence of bits. Some files are enormous: a single minute of uncompressed 4K video consumes roughly 20 gigabytes of storage. Without compression, our hard drives would fill up in minutes, streaming services could not exist, and sending an email attachment would be a test of patience.

Compression solves this problem by reducing file sizes, but it does so in two fundamentally different ways: lossless compression, which preserves every single bit of the original data, and lossy compression, which permanently discards some information to achieve much smaller file sizes.

Understanding the difference between these two approaches is not just academic — it directly affects the quality of your images, the fidelity of your music, the clarity of your videos, and the integrity of your documents. Making the wrong choice can mean irreversible quality degradation or unnecessarily bloated files.

This guide explains everything you need to know about lossless and lossy compression, compares the two approaches across every major media type, and gives you practical guidance on when to use each.

How Compression Works: The Basics

Lossless Compression

Lossless compression works by finding and eliminating statistical redundancy in data without removing any information. Think of it like a more efficient way to describe the same thing.

For example, instead of storing "AAAAAABBBCCCC" (13 characters), a lossless algorithm might store "6A3B4C" (6 characters). The original data can be perfectly reconstructed from the compressed version. Not a single bit is lost.

Common lossless compression algorithms include:

• DEFLATE — used in ZIP, PNG, and gzip
• LZW — used in GIF and early TIFF
• Huffman coding — foundational algorithm used in many formats
• FLAC — designed specifically for audio
• Run-length encoding — the simplest compression method (the AAABBB example above)
• Brotli — modern algorithm used for web compression

Lossy Compression

Lossy compression achieves much greater size reduction by permanently removing information that the algorithm considers least important. For visual media, this typically means discarding details that the human eye or ear is least likely to notice.

Lossy compression exploits the limitations of human perception:

• Visual perception — We are less sensitive to fine color differences than brightness differences, and we struggle to see detail in very complex textures
• Auditory perception — We cannot hear very quiet sounds that occur alongside much louder sounds (auditory masking), and we cannot perceive frequencies above roughly 20 kHz
• Temporal perception — In video, rapid motion reduces our ability to perceive fine detail in individual frames

Common lossy compression techniques include:

• Discrete Cosine Transform (DCT) — used in JPEG, MP3, and many video codecs
• Wavelet transform — used in JPEG 2000
• Psychoacoustic modeling — used in MP3, AAC, and Vorbis
• Motion compensation — used in video codecs like H.264 and H.265

Lossless vs Lossy: Head-to-Head Comparison

Compression in Images

Image compression is where the lossless vs lossy distinction is most visible and most frequently encountered.

Lossless Image Formats

PNG (Portable Network Graphics) is the most popular lossless image format. It excels at images with sharp edges, text, line art, and areas of flat color. PNG uses DEFLATE compression and supports transparency (alpha channel).

TIFF (Tagged Image File Format) supports both lossless and lossy compression. In its lossless mode (using LZW or ZIP compression), TIFF is the preferred format for print production, medical imaging, and scientific photography.

WebP (Lossless mode) is Google's modern format that offers lossless compression 26% smaller than PNG, according to Google's benchmarks.

BMP and RAW are uncompressed or minimally compressed formats used as source material.

Lossy Image Formats

JPEG (Joint Photographic Experts Group) is the dominant lossy image format. It uses DCT-based compression and offers a quality slider from 1 (maximum compression, lowest quality) to 100 (minimum compression, highest quality). JPEG is ideal for photographs and complex images with smooth gradients.

WebP (Lossy mode) provides 25-35% smaller files than JPEG at equivalent visual quality.

AVIF is the newest contender, offering roughly 50% better compression than JPEG with support for both lossy and lossless modes, HDR, and wide color gamut.

HEIF/HEIC is Apple's preferred format, using the HEVC codec for approximately 50% better compression than JPEG.

When to Use Each for Images

For more on the image format decision, see our detailed comparison of PNG vs JPG and our guide on compressing images without quality loss.

Compression in Audio

Audio compression follows the same lossless vs lossy divide, but the perceptual models are based on psychoacoustics rather than vision.

Lossless Audio Formats

FLAC (Free Lossless Audio Codec) is the most popular lossless audio format. It typically reduces file sizes by 50-70% compared to uncompressed WAV, while preserving every sample of the original audio. FLAC is the gold standard for music archiving and audiophile listening.

ALAC (Apple Lossless Audio Codec) is Apple's equivalent of FLAC, natively supported on all Apple devices and in iTunes/Apple Music.

WAV and AIFF are uncompressed audio formats. They preserve perfect quality but result in very large files (approximately 10 MB per minute for CD-quality audio).

Lossy Audio Formats

MP3 (MPEG Audio Layer III) is the most ubiquitous lossy audio format. At 320 kbps, MP3 is generally considered "transparent" (indistinguishable from the original) by most listeners. At 128 kbps, compression artifacts become noticeable, especially in complex passages with cymbals, strings, or vocals.

AAC (Advanced Audio Coding) is the successor to MP3, offering better quality at equivalent bitrates. It is the default format for Apple Music, YouTube, and many streaming services.

Vorbis and Opus are open-source lossy codecs. Opus in particular is considered the best lossy audio codec available, offering excellent quality at low bitrates (ideal for voice communication and music streaming).

Audio Quality at Different Bitrates

For context, CD-quality audio (16-bit, 44.1 kHz stereo) produces an uncompressed bitrate of 1,411 kbps. Here is how different lossy compression levels compare:

• 320 kbps MP3/AAC — Transparent for most listeners, nearly indistinguishable from the original
• 256 kbps AAC — Apple Music streaming quality, excellent for casual listening
• 192 kbps MP3 — Good quality, noticeable artifacts in critical listening
• 128 kbps MP3 — Acceptable for speech, noticeable quality reduction in music
• 64 kbps Opus — Excellent for voice, passable for music
• 32 kbps Opus — Adequate for voice communication

For a deep dive into the FLAC vs MP3 debate, read our comparison of FLAC vs MP3. Our FLAC converter makes it easy to convert between lossless and lossy audio formats, and our MP3 compressor helps you optimize audio file sizes.

Compression in Video

Video compression is by far the most complex domain because it combines spatial compression (within each frame, similar to image compression) with temporal compression (between frames, exploiting the fact that consecutive frames are usually very similar).

Lossless Video Codecs

Lossless video compression exists but produces enormous files. Common lossless codecs include:

• FFV1 — used primarily for archival purposes
• HuffYUV — fast lossless codec for editing workflows
• ProRes 4444 XQ — Apple's highest quality intermediate codec (technically near-lossless)
• DNxHR 444 — Avid's equivalent to ProRes

A single minute of lossless 1080p video can easily exceed 10 GB, making lossless video impractical for distribution.

Lossy Video Codecs

All commonly distributed video uses lossy compression:

• H.264/AVC — The most widely supported video codec. Used for everything from YouTube to Blu-ray
• H.265/HEVC — Roughly 50% better compression than H.264 at equivalent quality. Used in 4K streaming
• VP9 — Google's open-source alternative to HEVC. Used by YouTube for high-quality streams
• AV1 — The newest open-source codec, offering 30% better compression than HEVC. Adopted by Netflix, YouTube, and major streaming platforms

Understanding Video Bitrate

Video quality is primarily determined by bitrate (measured in Mbps):

• 4K streaming (Netflix): 15-25 Mbps (H.265)
• 1080p streaming: 5-8 Mbps (H.264)
• 720p streaming: 2.5-5 Mbps
• 480p streaming: 1-2.5 Mbps
• Blu-ray 1080p: 20-40 Mbps (H.264)
• 4K Blu-ray: 50-100 Mbps (H.265)

For guidance on compressing video while maintaining quality, read our guide on compressing video without losing quality.

Format Categorization Table

This comprehensive table categorizes common file formats by their compression type across all media categories:

*GIF uses lossless compression but is limited to 256 colors, so converting a full-color image to GIF is itself a lossy process.

The Problem of Generation Loss

One of the most important concepts in compression is generation loss — the cumulative quality degradation that occurs when a lossy-compressed file is decoded and then re-encoded.

How Generation Loss Works

1. You take a photograph. The camera saves it as a JPEG (first lossy compression)
2. You open the JPEG in an editor, make a small crop, and save it as JPEG again (second lossy compression)
3. Someone else opens your JPEG, adds a text overlay, and saves as JPEG again (third lossy compression)

Each save cycle introduces additional artifacts. After several generations, the quality degradation becomes severe and obvious — blocky artifacts, color banding, smeared details, and ringing around edges.

Generation Loss in Audio

The same principle applies to audio. Re-encoding an MP3 file to MP3 degrades quality with each generation. This is why musicians and audio engineers always work with lossless source files (WAV, FLAC, or AIFF) and only export to MP3 or AAC as the final step.

Generation Loss in Video

Video is particularly susceptible to generation loss because of the extreme compression ratios involved. Re-encoding an already-compressed video with a different codec, bitrate, or resolution always reduces quality. This is why video editors use intermediate codecs (ProRes, DNxHR) during editing — these codecs apply minimal compression to preserve quality through multiple edit cycles.

How to Avoid Generation Loss

• Always keep the original, uncompressed or losslessly compressed file
• Edit using lossless formats (PNG for images, FLAC/WAV for audio, ProRes for video)
• Only convert to lossy formats as the final delivery step
• Never re-encode a lossy file to the same lossy format
• If you must edit a lossy file, avoid re-saving in the same format — convert to a lossless format first

Choosing the Right Compression for Your Workflow

For Photographers

• Shoot in RAW for maximum editing flexibility
• Edit in RAW or TIFF (lossless)
• Export to JPEG or WebP for web delivery
• Archive in DNG or TIFF for long-term storage
• Use our image compressor to optimize delivery files

For Musicians and Podcasters

• Record in WAV (uncompressed) at the highest quality your equipment supports
• Edit in WAV throughout the production process
• Master and export to WAV or FLAC for archival
• Convert to MP3 or AAC for distribution
• Use our MP3 compressor to optimize audio for distribution

For Video Creators

• Record in the highest quality your camera supports (ProRes, RAW, or high-bitrate H.264/H.265)
• Edit using ProRes or DNxHR intermediate codecs
• Export to H.264 or H.265 for distribution
• Archive original footage on reliable storage
• Use our video compressor for optimized delivery

For Document Publishers

• Create documents in their native format (Word, InDesign, etc.)
• Export to PDF for distribution, using appropriate compression settings for embedded images
• Use lossless image compression for PDFs that will be printed
• Use lossy image compression (JPEG, medium quality) for PDFs distributed only digitally
• Our PDF compressor can reduce PDF sizes while maintaining readability

Technical Deep Dive: How Lossy Compression Decides What to Remove

In Images (DCT-Based Compression)

JPEG compression works by:

1. Converting the image from RGB to YCbCr color space (separating brightness from color)
2. Downsampling the color channels (chroma subsampling — typically 4:2:0, which halves color resolution)
3. Dividing the image into 8x8 pixel blocks
4. Applying the Discrete Cosine Transform to each block, converting spatial data into frequency data
5. Quantizing the frequency coefficients — dividing by a quantization matrix and rounding. This is the lossy step. High-frequency details (fine textures) are aggressively rounded, while low-frequency information (gradual transitions) is preserved
6. Applying lossless entropy coding (Huffman or arithmetic) to the quantized coefficients

The quality slider in JPEG controls how aggressive the quantization step is. Lower quality means more aggressive quantization, more data discarded, and smaller files.

In Audio (Psychoacoustic Modeling)

MP3 and AAC compression work by:

1. Analyzing the audio using a psychoacoustic model that identifies which frequencies the human ear can and cannot perceive in each time window
2. Applying the Modified Discrete Cosine Transform (MDCT) to convert audio from the time domain to the frequency domain
3. Allocating bits based on perceptual importance — more bits for perceptually important frequencies, fewer (or zero) bits for masked or inaudible frequencies
4. Encoding the result using Huffman coding

In Video (Motion Compensation)

Video codecs like H.264 and H.265 use three types of frames:

• I-frames (Intra): Compressed independently, like a JPEG image
• P-frames (Predicted): Store only the differences from the previous frame
• B-frames (Bidirectional): Store differences from both previous and future frames

This temporal compression is enormously effective because most of the pixels in a typical video frame are identical or very similar to the corresponding pixels in adjacent frames.

Common Myths About Compression

Myth: "Lossless is always better"

Not necessarily. For distribution and consumption, lossy compression at the right settings produces files that are perceptually indistinguishable from the original while being dramatically smaller. Serving lossless images on a website would cripple page load times without any visible quality improvement.

Myth: "Converting a lossy file to lossless improves quality"

This is completely false. Converting a JPEG to PNG does not restore the data lost during JPEG compression. The PNG file will be larger but contain exactly the same quality as the JPEG. You cannot create information that was already discarded.

Myth: "Higher JPEG quality numbers always mean better quality"

JPEG quality settings have diminishing returns. The difference between quality 70 and 80 is usually noticeable. The difference between quality 95 and 100 is often imperceptible, but the file size at quality 100 can be several times larger than quality 95.

Myth: "MP3 at 320 kbps is as good as FLAC"

In double-blind listening tests, most people cannot distinguish between 320 kbps MP3 and FLAC on typical consumer equipment. However, the lossless FLAC file preserves the option to re-encode to any format without generation loss, while the MP3 does not.

Practical Recommendations

For most people, the following rules of thumb will serve well:

1. Always keep your originals. Storage is cheap. Regret is expensive.
2. Use lossless for anything you might edit later. Once you discard data with lossy compression, you cannot get it back.
3. Use lossy for final delivery. The size savings are substantial and the quality difference is usually imperceptible when using appropriate settings.
4. Never re-compress lossy files. Each re-compression cycle degrades quality. If you need to edit a lossy file, keep the edited version in a lossless format.
5. Match the format to the content. Use JPEG/WebP for photos, PNG for graphics with text, FLAC for music archival, MP3/AAC for music distribution, H.264/H.265 for video.

Conclusion

Lossless and lossy compression are not competing technologies — they are complementary tools for different stages of the content lifecycle. Lossless compression preserves perfection at the cost of larger files, while lossy compression achieves dramatic size reduction by intelligently discarding information you are unlikely to miss.

The key is knowing when to use each. Master this distinction, and you will always deliver the best possible quality at the smallest possible file size, no matter what type of media you are working with.

Use our image compressor, video compressor, MP3 compressor, and PDF compressor to find the perfect balance between quality and file size for your specific needs.