Understand pixels, dpi and why images look soft
How pixel dimensions, ppi and print size relate, why images blur when scaled, what makes files big, and the size limits in Voidcanvas.
Beginner4 min readUpdated 25 September 2026Editor · Image size
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Resolution confuses people because one image can be called "72 dpi", "300 dpi" and "4000 pixels" all at once. Only the pixels are real. Once you understand that, you can tell in advance whether a photo is good enough for a poster, and why a sharp design turns soft after upload.
Pixels are the only real measure
A digital image is a grid of pixels, for example 2480 × 3508. That is all the detail it has. The dpi or ppi number stored in a file is only a note that says how big to print it. Change that note and the file prints at a different size, but no detail is added or lost.
ppi (pixels per inch) is how densely image pixels are laid onto paper. dpi (dots per inch) strictly means the ink dots a printer lays down, but most people and most apps, Voidcanvas included, say dpi for both.
The one formula
Print size in inches = pixels ÷ ppi. For millimetres, multiply by 25.4.
| Use | Target ppi at final size | Why |
|---|---|---|
| Flyers, cards, brochures, magazines | 300 | Read at arm's length; fine detail and small text show. |
| Posters read from a metre or two | 150 to 300 | Viewing distance hides detail. |
| Roll-up banners, billboards | About 100 to 150, or less for billboards | Seen from metres away. Ask the printer. |
So the A4 flyer preset, 2480 × 3508 px, is exactly A4 at 300 ppi (210 × 297 mm). The Poster 18 × 24 in preset in the Editor, 5400 × 7200, is 300 ppi. The Studio poster format of the same name is 2700 × 3600, which is 150 ppi: fine at viewing distance. Studio's roll-up banner at 2008 × 4724 px for 850 × 2000 mm works out at about 60 ppi. That holds up for big type and flat colour, but a detailed photo will look soft close up, so check with your printer.
Screens and "retina"
Screens do not care about dpi at all. A 1080 px wide post fills the width it is given. Modern phones pack two or three physical pixels into each layout pixel, so a graphic shown 400 px wide on a phone may be drawn with 800 to 1200 real pixels. Supply fewer and it gets stretched, which is where softness comes from.
Why images look soft
- Upscaling. Making a raster image bigger invents pixels by blending neighbours. It never adds real detail. Scale photos down freely, up as little as possible.
- Repeated resampling. Every resize blurs a little. Resize once, from the original, to the final size.
- Odd scale factors on screen. A 1000 px image shown at 1080 px is stretched by 8 per cent and every edge smears. Export at the exact size the platform uses.
- Compression. JPG and WebP throw away detail to save space. Sharp text and flat colour show blocky artefacts first.
- Platform recompression. Social networks recompress uploads. Starting from the exact platform size with a clean file gives them less to damage.
What makes a file big
In memory, every pixel takes 4 bytes (red, green, blue, alpha). A 2480 × 3508 layer is about 33 MB uncompressed, and every layer holds its own. On disk, compression shrinks this:
| Format | Compression | Best for |
|---|---|---|
| PNG | Lossless. Keeps every pixel and transparency. | Graphics, text, logos, flat colour, anything with transparency. |
| JPG | Lossy. No transparency. | Photos. Quality 80 to 90 per cent is usually indistinguishable from 100. |
| WebP | Lossy here, with transparency. | Websites. Smaller than JPG at similar quality. |
Doubling width and height quadruples the pixels, so a 2× export is roughly four times the file size.
How Voidcanvas handles resolution
- Imported photos are capped. When you open or place an image larger than 4096 px on its longest side, it is scaled down to 4096 px. A photo filling an A3 page at 300 ppi (3508 × 4961) is therefore at most about 248 ppi, and one filling the 18 × 24 in poster about 170 ppi. Both usually print well, but know the limit.
- Text and shapes stay sharp at any size. They are redrawn at the export size, so a 2× or 3× export of text is crisp. Photos and painted layers are resampled and cannot gain detail.
- Image size (Image menu, Ctrl+Alt+I) scales every layer. It shows the size in pixels, about how many MB each layer takes, and what that prints at in centimetres at the Resolution you enter. Change the Resolution to see a different print size.
- Export as… (Ctrl+E) offers 0.5×, 1×, 2× and 3×, showing the pixel size of each. Scales that would go over 8192 px on the longest side are not offered.
- Custom size on the start screen accepts 16 to 8000 px per side.
On a Mac, use Cmd in place of Ctrl.
Good to know
- A "72 dpi" file is not low quality. Check its pixel dimensions. A 3000 px wide file at 72 dpi is the same image as a 3000 px file at 300 dpi.
- Save a version before a big resize. The Image size dialog saves one for you when the new size is over 4000 px, and warns you above 8000 px that the browser may slow down.
- Phone screenshots of designs are not originals. They are resampled to the screen. Work from the source file.