Clarify various aspects of interpreting DIBs with compression of BI_BITFIELDS

[peteroupc]

Type of issue

Missing information

Feedback

This feedback relates to Windows device-independent bitmap (DIB) formats with the BI_BITFIELDS compression mode.

Clarify the meaning of bV4ClrUsed of BITMAPV4HEADER (and the like member of BITMAPINFOHEADER and BITMAPINFOV5HEADER) when bV4Compression is BI_BITFIELDS. Is this member 0 in this case? Is this member equal to 3, the size of bmiColors, or the number of colors in the color table if any? Can the DIB contain both a color table and color masks?

Also, clarify the valid choices for color masks. For example, can one of the color masks be zero?

Finally, clarify the conversion of color components to 8 bits per color component, especially when the color masks reflect that a color component has fewer than 8 bits.

Also, the documentation for BITMAPV4HEADER says bV4V4Compression in one place, rather than bV4Compression.