Image quality vs file size: how to find the right balance
What the quality slider really does, which settings to use for websites, email, print and forms, and how to check that small files still look sharp.
· 5 min read
Every lossy image is a trade: a smaller file in exchange for some detail. Pushed too far, photos turn blocky and text turns fuzzy. Not pushed far enough, pages load slowly and uploads fail. This guide explains what the quality setting actually controls and gives settings that hold up for the most common jobs.
What the quality number means
The quality setting is not a percentage of the original. It tells the encoder how coarsely to round away fine detail: lower numbers round more aggressively. Each encoder has its own scale, so quality 75 in one app is not the same as 75 in another, and the same number gives different sizes in JPG, WebP and AVIF.
The relationship is also far from even. At the top of the scale, file size rises steeply for detail nobody can see: going from 90 to 100 can nearly double a file. In the middle, between about 70 and 85, files shrink a lot while the picture barely changes. Below about 50, artifacts start to show on most photos. That is why Graviton’s quality slider starts at 75, labeled “Balanced”.
The same number means different things in each format
Quality 75 as a JPG, a WebP and an AVIF gives three different file sizes and three slightly different looks. Newer formats spend their bytes more cleverly, so at a similar visual quality WebP is usually 25–35% smaller than JPG and AVIF is often around half the size. When you switch formats, judge by eye and by file size, not by keeping the number the same.
Every save costs a little
Lossy compression is not a one-time cost if you keep re-saving. Opening a JPG, editing it and saving it again compresses it a second time, and the artifacts build up. Keep a full-quality master, make every compressed version from it, and never use a compressed copy as the starting point for the next one. If you only have a compressed file, use a gentle setting. Graviton hands back your original image, pixel for pixel, when it cannot make it smaller, so you never end up with a bigger file.
Where compression shows first
- Skies, walls and gradients. Smooth areas show blocks or bands of color first.
- Text and sharp edges. Lettering and thin lines pick up a fuzzy halo, especially in JPG.
- Saturated reds and blues. Color is stored in less detail than brightness, so small red details can bleed.
- Fine texture. WebP and AVIF tend to smooth hair, grass and fabric rather than make blocks, which looks cleaner but can look “painted” at very low quality.
Faces matter most to viewers, and noise-free, evenly lit photos compress best, so good light at capture time saves bytes later.
Recommended settings
These use Graviton’s quality scale (5–100). They are starting points; check the result for your own images.
| Use | Format | Quality | Max dimensions |
|---|---|---|---|
| Website photos | WebP | 75 | 1920 px |
| Full-width hero images | WebP or AVIF | 75–80 | 2560 px |
| Thumbnails | WebP | 70 | 800 px |
| Email attachments | JPG | 75 | 1600 px |
| Social media uploads | JPG | 80–85 | 1080–2048 px |
| Prints and archives | JPG | 90 or higher | Original |
| Screenshots and graphics | PNG | Default, or Lossless | Original |
| Forms with a size limit | JPG | Exact file size | Original (shrink to fit if offered) |
Social platforms re-compress everything you upload, so give them a slightly higher quality than you would use on your own site. Each extra round of compression costs a little detail.
Dimensions beat quality
Before you lower quality, check the dimensions. A 4000 × 3000 photo resized to 1920 × 1440 keeps only 23% of its pixels, and on a laptop screen it looks identical. You get most of the saving without touching quality at all. Lowering quality on an oversized image does the opposite: it degrades every pixel, including the ones nobody will ever see at full size.
In Graviton, turn on Resize and type the width you need, such as 1920, or pick a size such as Full HD. Proportions are kept, and in a batch smaller images stay as they are. The image resizer starts with 1920 pixels ready.
Compress JPEG imagesTry a few quality settings on your own photo and compare before and after.How to test the result
- Compress one typical image at 75 and look at it at the size it will be shown, not zoomed to 400%.
- Check the problem areas: faces, skies, text and saturated colors.
- Use the before-and-after slider to compare. If you cannot see a difference, try 65; if you can, try 85.
- Check on the device that matters. A phone screen hides more than a large monitor.
- Apply the setting you chose to the rest of the batch.
Compressing and comparing are unlimited and need no account; only downloads count against the free daily limit, so experiment freely.
When a size limit decides for you
Sometimes the number that matters is not quality but a maximum file size: 50 KB for an exam form, 1 MB for an email. Choose “Exact file size” as the goal, type the limit in KB or MB, and Graviton searches for the highest quality that fits. “Shrink dimensions if needed” is off by default, so your width and height stay the same and only the quality drops. Turn it on, or click “Shrink dimensions to fit” when Graviton suggests it, and it reduces the dimensions a little at a time instead, because a slightly smaller sharp image looks better than a full-size blocky one.
Our guide on compressing an image to a specific size covers what fits at each size, from 20 KB to 2 MB.
Compress an image to any size in KBType the size your form asks for and get the sharpest image that fits.When to go lossless
Use lossless when the exact pixels matter: screenshots for documentation, pixel art, images you will edit again, or graphics with fine text. In Graviton, “Lossless” under More options is available for PNG, WebP and AVIF. Files are larger, but nothing changes. For everyday PNGs, the default palette reduction in compress PNG is usually indistinguishable and much smaller.