PDF Lab / Original specimens

OBSERVED · REPRODUCIBLE · LIMITED

Check image clarity and preservation after saving

We placed 1200×800 and 240×160 images at the same printed size. Preserving source bytes cannot restore pixels that were already discarded.

Start with the problem

Symptom: An image saves successfully but its lettering and edges look soft when zoomed or printed.
Main cause: The placed size is too large for the available pixels. The comparison below changes source resolution while keeping placement size the same.
What to do now: Compare both PDFs at the same zoom level. Select the original image instead of a thumbnail, preserve its ratio and reduce its placed width and height, or obtain a larger source. Resizing the same image cannot create missing detail. Inspect the saved PDF at the size you will actually use.

The same 90×60 mm placement exposes the pixel difference

Both saved-PDF crops use the same position and scale. “1200×800” inside the artwork is part of the chart design; the headings below state the actual input dimensions.

Larger input · actually 1200×800 pixels. Placed at 90×60 mm. Look at the fine lines and TOP lettering. — **Larger input · actually 1200×800 pixels**
Placed at 90×60 mm. Look at the fine lines and TOP lettering.

Smaller input · actually 240×160 pixels. The same placement size. The same lines and lettering are softer. — **Smaller input · actually 240×160 pixels**
The same placement size. The same lines and lettering are softer.

Actual PDF crops: same region, 216 dpi. Select an image to open the full PDF.

What changed

Placement size is identical, but the smaller input lacks fine detail. Each JPEG’s own compressed input bytes are preserved inside its PDF.

Why it matters

Preserving compressed bytes cannot recover detail already missing from the source. The ppi table describes these placements, not universal print-quality pass marks.

What to do

Select the original rather than a messaging thumbnail. Preserve the ratio and reduce placement size for a small image, or obtain a larger source. Check the saved PDF at its intended use size.

Compare full pages and open the original PDFs

Measured observations

Item	Input / reference	Observed output
Original chart · 1200×800 pixels	1200 × 800 / 338.67 ppi	JPEG compression SHA-256 identical
Reduced chart · 240×160 pixels	240 × 160 / 67.73 ppi	JPEG compression SHA-256 identical

These observations apply to these specimens, not every PDF or reader.

Problem and inputs

We drew a chart of lines, corners and text, saved it as JPEG and reduced one copy to 240×160. Both are placed at 90×60 mm. The horizontal resolution in the table divides pixel width by placed width in inches.

What was inspected

We compare SHA-256 hashes of PDF DCTDecode image streams with the input JPEGs. For these unrotated JPEGs, the original compressed bytes match. Original text and image streams are checked separately. Zoom into the downloaded PDFs to compare the small inserted charts.

Keep useful detail

Import the original file instead of a repeatedly compressed messaging thumbnail.
Preserve proportions and avoid enlarging a small image unnecessarily.
Capture the relevant detail clearly and write explanations as separate searchable text.
Reopen the saved PDF and check page dimensions, image edges, extracted text and original images.

Limits of preservation checks

Matching hashes establish equality of that stream, not identical color management or printing in every reader. EXIF normalization converts to PNG, so compressed-byte equality is not expected there. Image checks alone say nothing about forms, links, attachments or tags; the app currently blocks editing those special structures.

Files to inspect yourself

Independent observations and method (JSON) · Authorship and file hashes

Crop coordinates, scale, source hashes and fresh extraction · Rechecked: 2026-10-24 · pdftoppm version 26.07.0 · pypdf 6.10.0 · pdfplumber 0.11.9. Original PDFs were not modified.

Environment, date and evidence boundaries

Checked: 2026-10-23 · Windows / Chrome 155 · pdf-lib 1.17.1 · PDF.js 6.4.299 · fontkit 1.1.1 · pypdf 6.10.0 · pdftoppm version 26.07.0. PDFs and artwork are original; NanumGothic uses OFL-1.1. Tables and files record direct observations; explanations interpret those structures. Physical OS keyboard input, phones and every PDF reader are outside this test.

Official reference explanations (separate from measurements): pdf-lib: embedding JPEG bytes

Reproduction code: scripts/lab-inputs.py, lab-outputs.mjs, lab-derived.py, tests/readiness-browser.mjs and tests/lab-pdf.py.

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