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IMGTool2PDF

Glossary

The terms used across the tools and guides, each explained the same way: what it means, why it matters when you are preparing a file, an example you can check the numbers on, and where the site puts it to work.

25 terms

6 terms

Image basics

Pixels, dimensions, ratios and crops — the geometry of a picture file.

  • Aspect ratio

    The proportional relationship between an image's width and height.

    What it means
    Aspect ratio is width compared with height, usually written as a ratio such as 3:2, 4:3, 16:9 or 1:1. It describes shape only — never size — so a 600 × 400 image and a 3000 × 2000 image share the same 3:2 ratio.
    Why it matters
    Forcing an image into dimensions with a different ratio stretches it. Crop or pad instead of scaling both axes independently, and the subject keeps its natural proportions.
    Example
    A 35 × 45 mm photo has a ratio of 7:9 (about 0.78). If your source photo is 4:3 (about 1.33), it is far wider than the target — filling the exact size by scaling alone would squeeze the face horizontally.

    Used by

  • Pixels

    The individual colour cells that make up a digital image.

    What it means
    A pixel is the smallest addressable element of a raster image — one stored colour value. An image's dimensions count pixels: 1200 × 800 means 1200 across and 800 down, or 960,000 in total.
    Why it matters
    Pixel count is what you are really changing when you resize, and it is the number requirements quote when they say “dimensions”. It also determines how large an image can be printed before the pixels themselves become visible.
    Example
    Halving both sides of a 2400 × 1600 image gives 1200 × 800: a quarter of the pixels, which is why the file usually shrinks by far more than half.

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  • Resolution

    How much detail an image carries, usually expressed as pixel dimensions.

    What it means
    For a digital image, resolution most often means the pixel dimensions — 1920 × 1080, for instance. In print contexts it can also mean pixel density (see DPI). The word is used for both, which is where most confusion starts.
    Why it matters
    “High resolution” is meaningless without context: 3000 pixels is high for an email attachment and modest for an A3 poster. Always compare resolution against the size you intend to display or print at.
    Example
    Two files both described as “high resolution”: a 4000 × 3000 camera photo destined for a 200 KB upload field, and a 400 × 300 thumbnail destined for nothing larger than a screen. The first needs reducing; the second does not.

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  • Crop

    Cutting away part of an image to change its shape without stretching it.

    What it means
    Cropping discards pixels outside a chosen rectangle. The remaining pixels keep their original values, so nothing is distorted — the image simply becomes smaller and often a different aspect ratio.
    Why it matters
    Crop is the correct way to reach an exact size when the source shape does not match. Unlike stretching, it never misrepresents a face, a logo or a line of text.
    Example
    A 1600 × 1200 photo that must become 1000 × 1000: crop a 1200 × 1200 square from the centre, then scale it to 1000 × 1000. Subject intact, sides trimmed.

    Used by

  • Resize

    Changing an image's pixel dimensions by scaling it up or down.

    What it means
    Resizing resamples the image: downscaling averages pixels together and discards detail; upscaling interpolates new pixels that did not exist, adding size but not information.
    Why it matters
    Downscaling is safe and is a powerful way to cut file size. Upscaling cannot recover detail — if an image is too small for a requirement, a better source is the real fix.
    Example
    A 400 × 400 photo upscaled to 1600 × 1600 has sixteen times the pixels and the same amount of detail; the file grows while the image stays soft.

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  • Scan

    Converting a physical page or card into a digital image or PDF.

    What it means
    Scanning captures a physical object as pixels or as a PDF page. The scanner's resolution setting determines how many pixels are captured per inch, which sets both the printable quality and the file size.
    Why it matters
    Scanning at a far higher DPI than needed inflates the file for no benefit; scanning too low makes text and detail hard to recover later. Match the DPI to what the document is actually for.
    Example
    A photo for an online form is usually fine scanned at 150–300 DPI, while a small print for reproducing later may justify 600 DPI — a fourfold increase in pixels per inch, and roughly four times the data.

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8 terms

File formats

What JPEG, PNG, WebP and PDF each store, and when to reach for them.

  • JPEG (.jpg)

    The default lossy format for photographs — small files, no transparency.

    What it means
    JPEG is a lossy image format: it discards visual detail to reduce file size, controlled by a quality setting when you save. It has no alpha channel, so it cannot store transparency, and it is accepted almost everywhere.
    Why it matters
    When a form lists accepted formats, JPEG is nearly always one of them, and it is the easiest format to drive inside a KB limit. For graphics with hard edges or transparency, it is the wrong choice.
    Example
    A 3000 × 4000 camera photo at 4 MB saved as JPEG quality 85 might land around 400–900 KB — a fraction of the size, usually with no visible difference at normal viewing distance.

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  • PNG (.png)

    A lossless format with transparency — best for graphics, text and cut-outs.

    What it means
    PNG stores pixels losslessly, so nothing is discarded on save, and it supports full alpha transparency. It is excellent for logos, screenshots, line art and anything with text; poor for photographs, which it stores much larger than JPEG.
    Why it matters
    Signatures and logos need PNG so transparent backgrounds survive. Photographs in PNG are usually far larger than necessary, which is a common reason a file will not fit a byte limit.
    Example
    A scanned signature at 1600 × 500 might be 900 KB as PNG and 60 KB as JPEG at quality 90 — but only the PNG keeps the background transparent.

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  • WebP (.webp)

    A modern format that is usually smaller than JPEG at the same quality.

    What it means
    WebP supports both lossy and lossless compression plus transparency, and generally produces smaller files than JPEG for comparable visual quality. Current browsers support it; older desktop software and many upload portals do not.
    Why it matters
    WebP is a strong choice for websites and listings where the platform allows it. For forms, portals and print shops, check acceptance first — a smaller file nobody will open helps nobody.
    Example
    The same photograph at quality 75 might be 180 KB as JPEG and 120 KB as WebP. If the form accepts only JPEG and PNG, the 60 KB saving is irrelevant.

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  • PDF

    A fixed-layout document format that preserves appearance across devices.

    What it means
    PDF describes pages as a fixed layout — text with embedded fonts, vector graphics and placed images — so a document looks the same wherever it is opened. Each page carries its own dimensions and orientation.
    Why it matters
    Because pages are fixed, PDF is what you build when appearance must survive being sent to someone else. It is also why page size, order and orientation are properties you have to set deliberately.
    Example
    A 200-page text report can be under 1 MB because text is stored as instructions, while a 20-page photo document can be 40 MB because every page carries image data.

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  • File format

    How a file's contents are encoded, independent of its name.

    What it means
    The format is what is actually inside the file — JPEG, PNG, PDF, ZIP — as distinct from the extension, which is only a label. A file named photo.jpg that contains PNG data is still a PNG.
    Why it matters
    Upload systems usually validate the real format rather than the name. Checking the actual format before submitting avoids the most common “invalid file” rejection.
    Example
    An image exported from a phone as IMG_1234.jpg that was actually re-saved as PNG can be several times larger than expected and still be rejected by a form expecting JPEG.

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  • Transparency

    Areas of an image with no colour, so whatever is behind shows through.

    What it means
    Transparency is carried in an alpha channel: each pixel has a coverage value from fully opaque to fully transparent. PNG and WebP support it; JPEG does not.
    Why it matters
    A cut-out signature, a logo or a product photo with the background removed must stay in a format with alpha, or the cut-out will be filled with a solid colour when it is placed.
    Example
    A signature trimmed to transparent PNG placed over a form field looks like ink on the page; the same file saved as JPEG gets a white box around it.

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  • EXIF

    The metadata a camera or phone embeds in a photo when it is taken.

    What it means
    EXIF is a metadata block inside JPEG and HEIC files recording capture details: camera model, lens, exposure, date, GPS coordinates and sometimes orientation or DPI hints.
    Why it matters
    EXIF can enlarge a file, disclose where and when a photo was taken, and influence how a viewer rotates it. Stripping it is a common reason a file gets smaller after “just a metadata edit”.
    Example
    A holiday photo with location coordinates attached is still perfectly useful once the coordinates are removed — and usually tens of kilobytes lighter.

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  • Password-protected PDF

    A PDF whose content is encrypted, so it cannot be opened or reused without the password.

    What it means
    PDF encryption comes in two kinds: an open password that must be entered before the document opens at all, and a permissions password that lets the document open but restricts printing, copying or editing. Either way the content is encrypted on disk, so software reading the file must be given the key.
    Why it matters
    Tools that read a PDF locally — every PDF tool on this site — refuse an encrypted file rather than guess at it, because decrypting needs the password. A document that opens in your reader may still be encrypted: the reader stores or remembers the password for you. Producing an unlocked copy from the reader, where the permissions allow it, is the usual fix.
    Example
    A statement arrives with its password written in the covering email. It opens in the reader, but adding it to the merge tool reports that it is password-protected; unlocking it in the reader first, or printing it to a new PDF, makes the same pages merge normally.

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6 terms

File size & quality

Bytes, compression and the trade-offs behind a quality slider.

  • File size

    How many bytes a file contains.

    What it means
    File size is the amount of data stored, measured in bytes and expressed in KB, MB or GB. For images it is driven by pixel count, how the pixels are encoded, and how much detail the content contains.
    Why it matters
    Byte limits are the requirement most often stated and most often failed, because they cannot be judged by looking at the file. Always measure rather than estimate.
    Example
    Two 12-megapixel photos: a flat sky at 600 KB and a gravel path at 4 MB — identical dimensions, wildly different content complexity.

    Used by

  • KB and MB

    Thousands and millions of bytes — the units limits are quoted in.

    What it means
    KB means kilobyte (about a thousand bytes) and MB means megabyte (about a million bytes). Strictly, 1 MB is 1000 KB under decimal conventions and 1024 KB under binary ones — both conventions are in active use.
    Why it matters
    A file that looks compliant under one convention can be slightly over under the other. Leave a margin below any stated maximum rather than landing exactly on it.
    Example
    A limit of “50 KB” is 50,000 bytes on one convention and 51,200 on the other. Aiming for 45 KB satisfies both.

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  • Compression

    Reducing a file's size by storing its data more efficiently.

    What it means
    Compression reduces the number of bytes needed to store data. Lossless compression removes redundancy without changing content; lossy compression also discards detail that is harder to perceive.
    Why it matters
    Knowing which kind you are using tells you whether the content will be identical afterwards. Photographs usually need lossy compression to reach tight limits; text and line art should stay lossless.
    Example
    Turning a photo from PNG to JPEG is a lossy step that often cuts size dramatically; recompressing a PNG with different settings changes almost nothing, because PNG already stores the data exactly.

    Used by

  • Lossy compression

    Compression that discards some detail in exchange for a much smaller file.

    What it means
    Lossy compression permanently removes information judged unlikely to be noticed, controlled by a quality setting. The discarded detail cannot be recovered later — each further save discards a little more.
    Why it matters
    This is why quality is a dial and not a switch: you decide how much is acceptable for your purpose. It is also why you should compress once from the original rather than repeatedly.
    Example
    Quality 95 retains almost everything; quality 75 is often visually close and much smaller; quality 40 on a face usually shows obvious blocking.

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  • Lossless compression

    Compression that reduces size while keeping every original value intact.

    What it means
    Lossless compression finds redundant or repeated data and stores it more compactly. Decompressing returns exactly the original bytes — nothing is discarded.
    Why it matters
    PNG, ZIP and the text and vector parts of a PDF are lossless. If the content must remain exact — text, line art, contracts — stay lossless and reduce size by other means.
    Example
    A flat-colour logo compresses extremely well losslessly; a photograph of the same dimensions barely benefits, because photographic detail has little redundancy to exploit.

    Used by

  • Image quality

    How much visual detail an encoding keeps — the dial behind file size.

    What it means
    In a lossy format, quality is the setting that governs how aggressively detail is discarded. Higher quality retains more and produces larger files; the relationship is steep at the top and shallow at the bottom.
    Why it matters
    Quality usually moves file size far more than people expect, which makes it the first thing to adjust before touching dimensions and losing real detail.
    Example
    On a detailed photo, dropping from 95 to 75 often halves the file with little visible change; dropping from 55 to 40 saves less and costs noticeably more.

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Looking for something else?

The guides explain these terms in the context of a real job, and the FAQ answers the questions that come up around them.

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