Undetected errors

[svgeesus]

From Project Nayuki PNG file chunk inspector:

My program and pngcheck can correctly detect almost all common and serious file errors. pngcheck fails to detect some errors like bKGD overflow, tRNS overflow, tIME wrong day-of-month, sPLT duplicate name, iTXt wrong UTF-8, zTXt wrong compressed data.

TypeScript code which implements the above checks.

• bKGD overflow
• tRNS overflow
• tIME wrong day-of-month
• sPLT duplicate name
• iTXt wrong UTF-8
• zTXt wrong compressed data.

[svgeesus]

tIME day of month is now checked, see #29

[svgeesus]

Checking for well-formed UTF-8 iTXT could be done relatively simply using Flexible and Economical UTF-8 Decoder by Björn Höhrmann.

However, that depends on checking for compression, and decompressing the text field.

[svgeesus]

Checking for duplicate palette names could be done by building a list of (hash, string), comparing the hash of the current name against that list and (for correctness) doing a string compare in the case of a hash match.