Exam PhotoKB, pixels, cm and dpi: what an exam form is really asking for
Forms mix four different measures and rarely explain them. Once you see what each one measures, the rules stop looking strange.
Pixels: how many dots the picture has
A digital picture is a grid of tiny coloured dots called pixels. "200 × 230 pixels" means 200 dots across and 230 dots down. More pixels means more detail.
KB: how heavy the file is
KB (kilobyte) measures how much storage the file takes. It is not a size you can see. Two pictures with the same pixels can have very different KB, because a JPG can be saved at high or low quality. Lower quality throws away fine detail and makes the file lighter.
A photo straight from a phone camera is usually 2,000 to 5,000 KB. Exam forms want 20 to 200 KB. So the picture must be made smaller in pixels and saved at a suitable quality.
Centimetres: the size on paper
Centimetres describe a printed photo, such as the 3.5 cm by 4.5 cm passport size. A file has no centimetres of its own. When a notice gives centimetres for an upload, read it as the shape of the picture: 3.5 by 4.5 means a little taller than wide; 6 by 2 means a wide strip.
dpi: the bridge between the two
dpi means dots per inch: how many pixels are printed along one inch (2.54 cm). It converts paper size to pixels:
pixels = centimetres ÷ 2.54 × dpi
At 200 dpi, 3 cm becomes 236 pixels. IBPS rounds this to 240 for its 3 cm thumb impression. The cm to pixels page works this out for any size.
Why forms give a KB range and not one number
The largest KB keeps the exam body's storage and upload times under control. The smallest KB most likely works as a rough check on quality: a photo of only 2 KB is usually too blurred to recognise a face. Staying inside the range satisfies both.
How to change each one
- Too many KB: reduce the pixels first, then lower the JPG quality a little.
- Too few KB: start again from the original picture and save at higher quality. Do not enlarge a small, blurred picture; it stays blurred.
- Wrong shape: crop. Never stretch or squeeze a face to fit.
- Wrong type: save as JPG. PNG, HEIC and PDF are different file types.
The resize tool does these in the right order by itself.
Next step
Open the resize tool Find your exam's rules