People treat PNG versus JPEG as a file-size choice. For redaction it is also a stability choice. JPEG throws away information on every save. PNG does not. When you blur, pixelate, or black-box a region and then export, the encoder decides what survives at the boundary between covered and uncovered pixels. On JPEG that boundary is where compression artifacts concentrate.
Which cover mode actually destroys samples is blur vs pixelate vs black box. A single-image blur session is blur an image online. This page is the format layer: why the same blur looks different after export, and why HideShot defaults to PNG download.
Guide
JPEG and PNG store images differently. JPEG uses discrete cosine transform on 8×8 blocks, quantizes coefficients, and Huffman-codes the result. Detail at sharp edges — including the edge of a black box or the falloff of a Gaussian blur — is expensive in bits. The encoder approximates. PNG stores filtered scanlines with lossless DEFLATE. What you painted on the canvas is what the file holds, modulo color profile conversion.
Redaction is not ‘make it hard to read at phone size.’ It is ‘change or destroy samples in the region you will send.’ Format affects whether those samples stay stable when the file is opened again, recompressed by a chat app, or zoomed on a desktop.
What happens when you blur then save as JPEG
You start from a camera JPEG that was already lossy. You draw a blur kernel over a credit-card stripe. The canvas mixes neighboring pixels into a smooth ramp at the blur edge. Export to JPEG again. The encoder sees high-frequency transitions at the blur rim and at text serifs just outside the blur. Block boundaries align with those transitions. Ringing — a faint echo of the old edge — can appear. Blockiness — visible 8×8 squares — can appear inside what should be a uniform smear.
A heavy pixelate mosaic on JPEG can look ‘good enough’ at 100% on a phone and still show a grid at 400% because the mosaic cells interact with JPEG blocks. A solid black fill suffers less because the interior is flat; the risk is still at the margin where black meets photo detail.
PNG export after the same cover operation keeps the ramp or mosaic cells as stored values. There is no second quantization pass inside HideShot’s download. The trade is file size. A 12 MP screenshot as PNG can be large. For evidence, IDs, and account numbers, size is the cheaper problem.
Why photographers still deliver JPEG — and when that is wrong for redaction
JPEG exists because lossy compression is excellent for natural photos at reasonable bitrates. Social platforms re-encode JPEG anyway. For a landscape with no secrets, JPEG is fine. For a redacted document photo, you are asking the codec to preserve a deliberate destruction pattern through a channel that assumes smooth skies and skin tones, not artificial step edges.
Workflow mistake: blur in an editor, ‘Save As JPEG quality 60’ to shrink, attach. You added a generation. Workflow improvement: cover here, download PNG, verify at zoom, then if you must hit a size cap, one controlled JPEG export with high quality — and inspect again. Do not iterate blur-save-blur on JPEG.
PNG sources versus JPEG sources on the same tool
Opening a PNG screenshot into the canvas starts lossless. Opening a JPEG starts with whatever artifacts the camera or screenshot tool already baked in. HideShot does not magically remove prior JPEG damage. Cover operations are applied on what is loaded. Export as PNG preserves the cover without adding a new lossy pass. That is the practical difference users feel: PNG in, PNG out is the cleanest chain.
HEIC and WebP are their own containers; browsers decode them to bitmaps for canvas. The export question is the same: PNG download avoids an extra lossy write. Conversion to JPEG afterward is a separate decision you control once.
How to use HideShot with format in mind
- Drop the image. Prefer the highest-quality copy you have (PNG screenshot beats re-forwarded JPEG).
- Black-box identifiers. Use blur or pixelate only when you will zoom-check the export — see blur vs pixelate vs black box.
- Download PNG. Open it. Walk the boundary of every cover region past 100% zoom.
- If a platform demands JPEG, convert once, re-inspect. Do not let the platform be the first JPEG generation after cover if you can avoid it.
Mistakes
Blurring on JPEG, saving JPEG, sending through WhatsApp (another re-encode). Three lossy steps. Edge artifacts compound.
Assuming blur ‘failed’ because JPEG shows rings. The cover may still be unreadable; the integrity question is whether artifacts leak shape at the rim. Pixelate heavily or black-box if the rim matters.
Choosing JPEG only for email size while the secret is still in an unmarked original elsewhere. Format does not replace covering the right file.
Cover mode choice: blur vs pixelate vs black box. Tool walkthrough: blur an image online.