What is UnderKB? Exact image and PDF compression explained

You have seen the error message: "File size must be less than 50 KB." Your photo looks fine. The portal does not care. It wants a number — and your file is 63 KB.

UnderKB exists for exactly this moment.

UnderKB is Logic Spine's file compression product built around one idea: portals do not ask for "smaller." They ask for under a specific kilobyte limit. UnderKB lets you set that limit, compress your file, and download something that actually gets accepted.

Tagline: Stay under. Get accepted.

This article covers what UnderKB is, who uses it, how it works under the hood, and why we built it as a standalone product.

The problem UnderKB solves

Online portals — government sites, university admissions, competitive exams, job applications, visa systems — enforce hard file-size ceilings:

Upload type	Common limits
Signature scan	10–20 KB
Passport / ID photo	20–100 KB
Supporting image	50–200 KB
PDF document	150 KB – 2 MB

Generic compressors optimise for visual quality or rough size reduction. They do not guarantee you land under 50 KB — or exactly at 48 KB with room to spare.

The result is a frustrating loop:

1. Upload file
2. Get rejected
3. Guess a quality setting in an editor
4. Upload again
5. Repeat until you give up or miss the deadline

UnderKB breaks that loop. You set the target. The tool hits the target. You move on.

What UnderKB actually is

UnderKB is a web application at underkb.logicspine.com that compresses:

• Images — JPEG, PNG, WebP
• PDFs — Scanned documents, certificates, application attachments

You choose a target size in kilobytes (presets like 20, 50, or 100 KB, or a custom value), upload your file, and download a compressed output sized for your portal.

No desktop software install. Works in the browser on desktop and mobile. Can be installed as a PWA (Progressive Web App) for one-tap access during exam or application season.

Who UnderKB is for

UnderKB serves anyone who hits a kilobyte wall on an upload form:

User	Example scenario
Students	University admission or SSC form with 50 KB photo cap
Exam applicants	UPSC, state PSC, or entrance exam portals
Job seekers	Application sites with signature and photo limits
Travel applicants	Passport, visa, or OCI photo size rules
General users	Any government or banking portal with strict uploads

You do not need technical skill. If you can drag a file and type a number, you can use UnderKB.

How UnderKB works

1. Set your target KB

Enter the exact limit from the portal instructions — e.g. "maximum 50 KB" means set 50 (or slightly below, like 48, for safety margin).

UnderKB offers presets for common limits and a custom input for anything else.

2. Upload your file

Drag and drop or pick from your device. UnderKB accepts images and PDFs used in typical portal workflows.

Marketing pages can deep-link directly into the app with your target pre-filled — e.g. ?targetKb=50 — so you land ready to compress.

3. Compress — fast path first

UnderKB uses a dual processing strategy:

• Browser-first — For many images, compression runs locally in your browser. Fast, private, no server wait.
• Server fallback — When the browser cannot reach the target (large files, difficult PDFs, edge cases), UnderKB processes on secure cloud infrastructure and returns an optimised result.

You get the fastest path that works — not a one-size-fits-all pipeline.

4. Review and download

See the output size. If it is still over target, re-compress with a lower goal. Your recent files are saved locally so you can iterate without re-uploading from scratch.

5. Upload to your portal

Download the file. Upload once. Get accepted.

That is the entire value proposition — one tool, one target, one successful upload.

Key features in detail

Exact KB targeting

The core differentiator. UnderKB optimises for your number, not "about smaller." This is what generic tools and phone gallery "compress" options miss.

Images and PDFs

Photos for forms. Scanned signatures. PDF certificates capped at 200 KB or 300 KB. UnderKB handles both — because real applications mix image and document uploads.

Portal-ready output

Output formats and sizing aimed at acceptance, not just file-size metrics. Readable text on ID scans. Sharp enough passport photos for biometric checks.

Presets and deep links

Common targets (20 KB, 50 KB, 100 KB) are one click away. Landing pages for passport photos, visa images, exam signatures, and PDF limits route you into the compressor with sensible defaults.

Recent files library

Local history of your compressions. Need to shave another 2 KB? Hit reduce more without starting over.

Mobile-friendly UX

Form deadlines do not wait for you to reach a desktop. UnderKB's mobile experience includes gallery pickers, document selectors, and sticky actions — built for real phone usage during stressful application nights.

Optional Google sign-in

Anonymous compression works for most users. Sign in with Google for higher limits and future account features as the product grows.

Installable PWA

Add UnderKB to your home screen. During exam season or visa crunch time, the compressor is one tap away — like an app, without an app store.

UnderKB's tool and guide ecosystem

Beyond the main app at /app, UnderKB includes a large SEO and help surface for high-intent searches:

• Tool hubs — Image compression, PDF compression, signature tools, photo tools
• Size-specific pages — "Compress image to 20 KB", "PDF under 200 KB"
• Guides — Step-by-step stories for SSC signatures, passport photos, university forms

If you are researching before compressing, start at underkb.logicspine.com/tools. If you already know your limit, go straight to underkb.logicspine.com/app.

UnderKB vs generic online compressors

	Generic compressor	UnderKB
Goal	Smaller file	Under exact KB limit
PDF support	Often missing or basic	Built-in pipeline
Presets	Quality %	20 KB, 50 KB, 100 KB…
Retry loop	Manual guesswork	Targeted re-compress
Portal context	None	Guides and landing pages per use case

UnderKB vs desktop editors

Photoshop, GIMP, and Paint can export JPEGs — but none are built around "must be under 50 KB for this government portal tonight." UnderKB is single-purpose software for a single-purpose frustration.

Why Logic Spine built UnderKB

Logic Spine builds custom software when off-the-shelf tools miss the mark. UnderKB started the same way — a real rejection message on a real form, followed by twenty minutes of quality-slider guessing.

The problem was specific enough to productise:

• Millions of Indians hit KB limits every application season
• Generic tools solve the wrong problem ("smaller" vs "under X KB")
• The fix is algorithmic, not consultative

So we shipped UnderKB as a focused product — fast, browser-first, with cloud fallback for hard cases — deployed on reliable infrastructure (Google Cloud) because upload season is not when you want downtime.

UnderKB is the consumer-facing product. Logic Spine is the company behind it — same team that builds Sumikar and custom solutions for clients.

Privacy and processing

• Browser compression keeps files on your device for eligible images
• Server processing uses signed uploads to secure cloud storage; temporary files are lifecycle-managed and deleted
• No requirement to create an account for basic use

For sensitive documents (ID scans, signatures), the browser-first path is designed to minimise unnecessary server exposure.

Frequently asked questions

Is UnderKB free?

Core compression is available for anonymous use. Sign-in unlocks higher limits. Check the app for current limits — they may evolve as we add subscription tiers.

Will UnderKB ruin my photo quality?

Compression always trades quality for size. UnderKB targets the maximum quality that fits your KB limit — not arbitrary crushing. For passport photos, start from a well-cropped source image for best results.

What if my portal also checks pixel dimensions?

UnderKB focuses on file size. Some portals also require specific width × height (e.g. 200×230 px). Crop to the required aspect ratio first, then compress to the KB limit. Our guides cover common dimension rules.

Can I use UnderKB for bulk or API compression?

A developer API is on the roadmap. For now, the web app serves individual uploads. Organisations with bulk needs can contact Logic Spine for custom integration.

UnderKB vs the Logic Spine blog article on passport photos

We also publish how-to guides on this site for SEO and education. UnderKB is the tool; the blog is the explanation. Use both — read the guide, compress in the app.

Getting started

1. Open underkb.logicspine.com/app
2. Note the KB limit from your portal's instructions
3. Set that as your target (or pick a preset)
4. Upload, compress, download
5. Upload to your portal — once

If you are not sure which limit applies, browse underkb.logicspine.com/tools for your scenario — passport, visa, exam, signature, PDF.

Stuck on a weird portal rule or need compression baked into your own product? Contact Logic Spine — we build custom document workflows when a standalone tool is not enough.

UnderKB — Stay under. Get accepted.