Flattened pixmap mask description wrong for small images -- Bug?

Question

I've been working with images loaded from disk lately, and it seems to me the description for the mask element of the flattened pixmap cluster is incorrect when the image size is small. The online help reads:
mask is an array of bytes in which each bit describes mask
information for a pixel. The first byte describes the first eight pixels, the
second byte describes the next eight pixels, and so on. If a bit is zero,
LabVIEW draws the corresponding pixel as transparent. If the array is empty,
LabVIEW draws all pixels without transparency. If the array does not contain a
bit for each pixel in the image, LabVIEW draws any pixels missing from the array
without transparency.
So there should be one bit in the mask for each pixel. Here is what I'm getting:
image size   # pixels    mask length, bytes (bits)
1x1               1            2   (16)
1x2               2            2   (16)
2x2               4            4   (32)
4x4              16            8   (64)
8x8              64           16  (128)
9x9              81           18  (144)
32x32          1024          128 (1024)
33x33          1089          198 (1584)
It looks like there are two issues here. One, the mask array works on rows of pixels. If the row does not end on a byte, the byte is padded on the right with zeros until the end, then the next row starts. E.g., for the 9x9 image, pixel #9 is byte 2, bit 8; byte 2 is padded with zeros; pixels 10-18 start with byte 3.
Two, for some reason small images (i think 8 pixels per row or less, but I'm not sure) have every other byte a zero. For example, here is the mask for my 4x4 test image, with every pixel opaque:
   11110000 00000000 11110000 00000000 11110000 00000000 11110000 00000000
According to thel help text, the mask array should be 2 bytes long, with every bit a 1.
It seems to me that the first issue is likely intentional, and the help text just isn't entirely clear. The second issue, I'm not sure about. Maybe it was just assumed that pictures would be large and small pictures wouldn't be used?

Answer 1

Wiebe is correct that every line of the image gets an even number of bytes in it mask.
The help was misleading, I agree. I have reported this confusion as a bug in the documentation (I do not remeber to CAR#) so it can be explained better.
Ben
Ben Rayner
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