Check the pixels you will actually print
A PNG can look fine on a white webpage while showing a pale outline on a dark shirt or a faint mark in an otherwise empty margin. Previewing the same artwork against several backgrounds makes these details easier to spot. The checker counts all source pixels; its on-screen preview is scaled to fit your device.
Fully transparent pixels have alpha 0, opaque pixels have alpha 255, and values between them are semi-transparent. Smooth anti-aliased edges, shadows and translucent artwork legitimately use partial transparency. A non-zero count does not mean the image is defective.
The optional review overlay marks alpha values from 1 to 31 in red and near-white, semi-transparent pixels in blue. These are simple review hints. They do not automatically identify isolated specks, certify a clean cutout or prove that a printed halo will occur. Small marks may disappear in the downsampled overlay, so inspect important details in your image editor too.
DPI metadata and effective PPI are different
Effective PPI is the number of image pixels divided by the intended printed size in inches. A 3,600-pixel-wide PNG printed 12 inches wide provides 300 PPI. At 24 inches wide the same file provides 150 PPI. Setting a 300 DPI metadata tag does not create extra pixels or recover missing detail.
Choose the target recommended by your print provider. This tool offers 150, 200, 300 and 600 PPI as calculation targets, not universal acceptance rules. The report shows whether the pixel density meets the target you selected. It does not judge viewing distance, substrate, printer settings, artwork sharpness or colour reproduction.
If you enter both width and height with a different aspect ratio from the source, the checker warns that printing at both dimensions would stretch the image. Leave height blank for a proportional calculation. Switching units converts the entered physical dimensions.
Transparent padding changes the size of your design
The full canvas includes transparent margins. The non-transparent bounds describe the smallest rectangle containing every pixel with alpha above zero, including very faint pixels. Both full-canvas and visible-bounds print sizes are shown at the selected target resolution.
A small design on a large transparent canvas does not fill the entire printed area. Crop intentionally in an image editor if you want to remove padding, then check the exported copy again. The checker preserves the source and does not silently crop, recolour or upscale it.
Static PNG files are supported up to 30 MB, 16 million pixels and 16,384 pixels per side. Animated PNGs are rejected because their frames require separate inspection. For another format, create a PNG with Image Converter. Use DPI Converter when you only need to change a density tag, or Resize Image for pixel dimensions.