Question 1

Why is my scanned PDF so large?

Accepted Answer

Because a scan is not a document — it is a **collection of photographs**, and it is stored as image data rather than as text.

**The difference.** A PDF created from a word processor stores **text characters** plus font and layout instructions, which is extremely compact — a long document may be a few hundred kilobytes. A scanned PDF stores a **picture of each page**, and the file size depends on pixel count and colour depth, not on how much is written.

**What drives the size:**

**Resolution (DPI).** Size scales roughly with the **square** of resolution. Scanning at 600 DPI produces a file around four times larger than 300 DPI. For text documents, **300 DPI is sufficient** for both readability and OCR accuracy, and higher adds size without benefit. 600 DPI is worth it only for very small print or archival photographs.

**Colour mode**, which is the biggest single lever. A page scanned in **24-bit colour** is roughly three times the data of greyscale and dramatically more than **bitonal** (pure black and white). Scanning plain printed text in full colour is the most common cause of an oversized file.

**Compression choice.** JPEG compression suits photographs and produces artefacts around text. **Group 4 / CCITT** compression is designed for bitonal text and is extremely efficient. **JBIG2** and **MRC** (mixed raster content) separate text from background and compress each appropriately, achieving very large reductions — this is what document scanners and "reduce file size" features use.

**No downsampling**, leaving the scan at capture resolution.

**Embedded thumbnails and metadata**, a smaller contributor.

**What to do:**

**Scan text at 300 DPI in black and white or greyscale.** This alone often reduces a file by 90%.

**Run OCR**, which adds a searchable text layer — usually small — and makes the document genuinely useful rather than an image.

**Use a PDF optimiser** to downsample and recompress existing files.

Question 2

Why does text look blurry on my monitor?

Accepted Answer

Usually a resolution or scaling mismatch rather than a fault, and the causes are distinguishable. Not running at native resolution. This is the most common cause. LCD and OLED panels have a fixed

Question 3

Why do my photos lose quality when I send them?

Accepted Answer

Because most messaging and social platforms recompress images on upload, and several also resize them — so what arrives is a smaller, more heavily compressed copy rather than the file you sent. What

Question 4

Why does my document look different on someone else's computer?

Accepted Answer

Because a word processor document is a set of instructions for laying out text, not a picture of a page — and those instructions are interpreted using whatever the receiving computer actually has

Question 5

Why are my photos HEIC, and why will nothing open them?

Accepted Answer

HEIC is the file extension for images stored in HEIF — the High Efficiency Image File Format — using HEVC compression. It became the default on iPhones some years ago, which is why photos that used

Question 6

Why does my drive show less storage than advertised?

Accepted Answer

Two separate reasons that compound, and only one of them is arguably anyone's fault. Reason one: decimal versus binary units. Storage manufacturers use decimal prefixes, where 1 GB means

Question 7

Why does copying files start fast then slow to a crawl?

Accepted Answer

Because the first portion of the transfer is being absorbed by a fast cache, and once that cache fills you see the device's real sustained speed. On SSDs: the SLC cache. Most consumer SSDs use TLC or

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