Low compression quality compared to cwebp CLI tool

Description

When using SDImageWebPCoder to encode images with lossless options, the resulting file size and compression quality appear to be worse compared to Google's cwebp command-line tool. Despite both using lossless compression settings, SDImageWebPCoder produces slightly lower quality images, with visible artifacts and banding on gradients and shadows.

I experimented with different encoding options such as: encodeCompressionQuality, encodeWebPMethod, encodeWebPPass etc. Despite these adjustments, the output quality and file size were still worse compared to cwebp -lossless. This suggests a fundamental difference in how the WebP encoding is implemented in SDImageWebPCoder versus the official WebP compression tool.

Code

SDImageWebPCoder:

if let data = SDImageWebPCoder.shared.encodedData(with: nsImage, format: .webP, options: [.encodeWebPLossless: 1]) {
  try data.write(to: destination))
}

cwebp:

cwebp -lossless input.png -o output.webp

Results

Inizia dal punto di ingresso della codifica senza perdita di SDImageWebPCoder mostrato nel report e confronta il suo output con cwebp -lossless usando l’esempio fornito. Verifica quali opzioni encodeCompressionQuality, encodeWebPMethod e encodeWebPPass vengono inoltrate, quindi considera il lavoro completato quando il comportamento di cwebp in termini di qualità senza perdita e dimensione del file corrisponde, oppure quando la differenza di implementazione è documentata.