Image Optimisation

PixelTamp uses native macOS frameworks for optimal hardware acceleration where possible, supplementing those with other embedded libraries to reduce file sizes where necessary.

Supported Image Formats

Format	Optimisation Method
JPEG / JPG	Strips superfluous metadata, applies progressive encoding, tuned chroma subsampling.
PNG	Quantises graphics to 8-bit palettes with perceptual guardrails, or applies lossless 24/32-bit Deflate compression for gradients.
WebP	Produces compact images with superior compression ratios for modern web browsers.
GIF	Minimises frame delta sizes or converts multi-megabyte GIFs into lightweight MP4 videos.
HEIC / HEIF	Reads iPhone and modern camera photos and outputs web-compatible formats.

PNG Quantisation & Adaptive Dithering

PNG files often contain 24-bit colour depth and an 8-bit alpha channel, resulting in hefty file sizes. PixelTamp features an intelligent, multi-tiered PNG pipeline:

Bit Depth Clamping: Normalises high bit-depth files (such as 16-bit per channel / 48-bit or 64-bit PNGs) down to standard web 8-bit channels, eliminating redundant data overhead while preserving visual detail.
Smart Adaptive Tamped Mode:
- Colour Ceiling: Scans unique colours with a generous threshold, quickly identifying vector graphics, logos, icons, and UI screenshots with anti-aliasing.
- Perceptual Guardrail: Reduces the image to 256 colours, checking shifts in colour and transparency to ensure the result looks virtually identical to the original before baking it in.
- Lossless Truecolour Fallback: If an image contains smooth continuous gradients or photographic colour ramps that exceed the threshold, PixelTamp automatically rejects quantisation and falls back to full 24/32-bit lossless Deflate compression, avoiding colour banding or noisy stippling.
Full 256-Colour Aggressive Mode: Unconditionally applies 256-colour palette reduction with Floyd-Steinberg error diffusion dithering for maximum compression in bandwidth-critical environments.
Alpha Channel Support: Fully preserves binary and partial alpha transparency. If an image is completely opaque, redundant alpha channels are stripped to save 25% of uncompressed raw pixel data.

All that said, PNG files are often misused where a JPEG would be more appropriate, with the misconception that they’re the best way to retain uncompromised image quality. PixelTamp can only optimise these images as far as the file format allows.

EXIF Orientation Normalisation

Digital cameras and smartphones write orientation metadata rather than physically rotating the pixel buffer. When stripping metadata for web privacy and byte reduction, other tools may render photos sideways or upside down.

PixelTamp automatically:

Detects EXIF orientation tags during ingestion.
Physically bakes the rotation into the pixel array using hardware-accelerated rendering.
Outputs a perfectly upright image that renders correctly in any browser or viewer.

Metadata Handling & Photo Licences

By default, PixelTamp follows a Preserve Copyright & Attribution policy:

Privacy Protection: Strips sensitive camera EXIF data, GPS coordinates, serial numbers, and device information to safeguard privacy and minimise file size.
Attribution Retention: Automatically retains creator names, copyright notices, credit lines, and usage terms across JPEG (IPTC/TIFF), PNG (Copyright and Author chunks), and WebP (Dublin Core XMP packets).

If you require complete anonymity and maximal byte reduction, you can select Strip All Metadata under Settings (Cmd + ,) > General.

Photo Licences & Metadata: Many third-party photo licences (such as Creative Commons attribution licences or commercial stock photography agreements) require copyright notices and creator attribution to remain intact. PixelTamp’s default setting preserves these rights terms by default, but it remains your responsibility to verify the licensing requirements of your source media.

Dimension Constraints (Downscaling)

PixelTamp allows you to constrain image dimensions based on the longest edge:

Original Size: Keeps native pixel dimensions untouched.
2560px (Default): Ideal for high-density Retina display hero banners.
1920px: Standard Full HD resolution for blog articles and content cards.
1024px: Compact size for thumbnails, avatars, and email newsletters.

You can also define your own presets under Settings (Cmd + ,) > Sizes.

PixelTamp operates strictly non-destructively: it will never upscale an image that is already smaller than the selected constraint.

Scope & Responsive Images

PixelTamp is built for primary asset compression. It is designed to compress source media or batches of pre-sized assets exported from design tools, rather than generating multiple srcset variants from a single file.