2.1.7 [W3C-PNG] Section, sBIT Significant bits


The specification states: sBIT Significant bits
 Each depth specified in sBIT shall be greater than zero and less than or equal to 
 the sample depth (which is 8 for indexed-colour images, and the bit depth given in 
 IHDR for other colour types). Note that sBIT does not provide a sample depth for 
 the alpha channel that is implied by a tRNS chunk; in that case, all of the sample 
 bits of the alpha channel are to be treated as significant. If the sBIT chunk is 
 not present, then all of the sample bits of all channels are to be treated as 

All Document Modes (All Versions)

The sBIT chunk is not supported.