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2008.10.31 17:10 "Data ordering for planar config separate", by Richard Nolde
I'm updating tiffcrop (my extended version of tiffcp) to support
images of arbitrary bit depth and I'm looking for documentation on the
actual layout of bit planes in strips for files with multiple strips and
multiple samples per pixel and how this affects the current routines to
read and write images using the scanline oriented routines. I managed to
get my code working for copying images of any bit depth from images with
planar config == contig to planar config = contig and to planar config =
separate and now I am trying to add support for reading images with
planar config = separate and bit depth != a multiple of 8 bits.
Tiffcp works for reading images with planar config == separate only if
the bits per pixel are a multiple of 8 bits. The current code that
merges data from separate planes into a single buffer assumes byte sized
samples and it loops through each scanline of the image for each sample
before moving to the next sample. I'm trying to determine if images that
contain multiple strips for each sample can be read by interleaving the
reads from each sample within a loop for each row of the image or
whether that violates the random access prohibition for compressed data.
I'd be reading sequentially within each plane, but jumping between
planes for successive reads. The only other alternative is to read each
plane into a separate buffer and then combine the values into the
combined buffer which will increase the memory requirement during the
read phase.
eg
for (row = 0; row < length, row++)
{
read scanline 1 for sample 1 into buff1
read scanline 1 for sample 2 into buff2
read scanline 1 for sample 3 into buff3
for (column = 0; column < width; column++)
packdata from buff1[column], buff2[column], buff3[column] into
combinedbuff[column]
}
The tiffdump of my 32 bit per sample image below indicates that the
strips are being written RRR, GGG, BBB
tiffdump /tmp/tiger-rgb-strip-planar-32.tiff
/tmp/tiger-rgb-strip-planar-32.tiff:
Magic: 0x4949 <little-endian> Version: 0x2a
Directory 0: offset 66584 (0x10418) next 0 (0)
ImageWidth (256) SHORT (3) 1<73>
ImageLength (257) SHORT (3) 1<76>
BitsPerSample (258) SHORT (3) 3<32 32 32>
Compression (259) SHORT (3) 1<1>
Photometric (262) SHORT (3) 1<2>
DocumentName (269) ASCII (2) 30<tiger-rgb-strip-planar-3 ...>
ImageDescription (270) ASCII (2) 53< Image generated by GPL ...>
StripOffsets (273) LONG (4) 9<8 8184 16360 22200 30376 38552 44392 52568
60744>
Orientation (274) SHORT (3) 1<1>
SamplesPerPixel (277) SHORT (3) 1<3>
RowsPerStrip (278) SHORT (3) 1<28>
StripByteCounts (279) LONG (4) 9<8176 8176 5840 8176 8176 5840 8176 8176
5840>
XResolution (282) RATIONAL (5) 1<72>
YResolution (283) RATIONAL (5) 1<72>
PlanarConfig (284) SHORT (3) 1<2>
ResolutionUnit (296) SHORT (3) 1<1>
PageNumber (297) SHORT (3) 2<1 0>
Software (305) ASCII (2) 65<GraphicsMagick 1.3 unrel ...>
SampleFormat (339) SHORT (3) 3<1 1 1>