Grayscale with Transparency

PNG supports two kinds of transparency with grayscale and RGB images. The first is a palette-style ``cheap transparency,'' in which a single color or gray value is marked as being fully transparent. I noted earlier that the structure of tRNS depends on the image type; for grayscale images of any pixel depth, the chunk contains a 2-byte, unscaled gray value--that is, the maximum allowed value is still 2^{bit depth}-1, even though it is stored as a 16-bit integer. This approach is very similar to GIF-style transparency in palette images and incurs only 14 bytes overhead in file size. There is no corresponding TIFF image type, and standard JPEG does not support any transparency.