Hello,
I'm having issues loading/displaying TIFF files that use tiles. I was using ImageEn v13.7.0, but updated to v14.0.1 to see if the issue has been resolved; it hasn’t. My problem can be seen using the demo TiffHandler application located at Demos\InputOutput\TiffHandler.
Following is some relevant info from the tiffdump utility:
.\LHAFTC03-1011_20240513.Tif:
Magic: 0x4949 <little-endian> Version: 0x2a
Directory 0: offset 8 (0x8) next 1311542 (0x140336)
SubFileType (254) LONG (4) 1<0>
ImageWidth (256) LONG (4) 1<1280>
ImageLength (257) LONG (4) 1<1024>
BitsPerSample (258) SHORT (3) 1<8>
Compression (259) LONG (4) 1<1>
Photometric (262) SHORT (3) 1<1>
SamplesPerPixel (277) LONG (4) 1<1>
XResolution (282) RATIONAL (5) 1<72>
YResolution (283) RATIONAL (5) 1<72>
PlanarConfig (284) SHORT (3) 1<1>
ResolutionUnit (296) SHORT (3) 1<1>
TileWidth (322) SHORT (3) 1<1280>
TileLength (323) SHORT (3) 1<1024>
TileOffsets (324) LONG (4) 1<698>
TileByteCounts (325) LONG (4) 1<702>
JPEGProcessingMode (512) SHORT (3) 1<14>
JPEGLosslessPredictors (517) SHORT (3) 1<1>
JPEGPointTransform (518) SHORT (3) 1<0>
JPEGDCTables (520) LONG (4) 1<426>
<snip of custom tags>
Directory 1: offset 1311542 (0x140336) next 0 (0)
SubFileType (254) LONG (4) 1<0>
ImageWidth (256) LONG (4) 1<1280>
ImageLength (257) LONG (4) 1<1024>
BitsPerSample (258) SHORT (3) 1<8>
Compression (259) LONG (4) 1<1>
Photometric (262) SHORT (3) 1<1>
SamplesPerPixel (277) LONG (4) 1<1>
XResolution (282) RATIONAL (5) 1<72>
YResolution (283) RATIONAL (5) 1<72>
PlanarConfig (284) SHORT (3) 1<1>
ResolutionUnit (296) SHORT (3) 1<1>
TileWidth (322) SHORT (3) 1<1280>
TileLength (323) SHORT (3) 1<1024>
TileOffsets (324) LONG (4) 1<1312232>
TileByteCounts (325) LONG (4) 1<1312236>
JPEGProcessingMode (512) SHORT (3) 1<14>
JPEGLosslessPredictors (517) SHORT (3) 1<1>
JPEGPointTransform (518) SHORT (3) 1<0>
JPEGDCTables (520) LONG (4) 1<426>
<snip of custom tags>
Note from the above that TileWidth is 1280 and TileLength is 1024 with Compression set to 1 (none). This being the case, the byte count for each tile should be 1310720 (1280 x 1024). You can see in the above data that TileByteCounts is not 1310720 which is fine because in both cases for the two IFDs the values are offsets from the beginning of the file.
I think a special case is being encounter because TileOffsets has a value/offset of 1 meaning there is only one tile per IFD. What I believe is happening is that because the data type for these tags is LONG (i.e., 4 bytes), and because there is only 1 tile per IFD, the ImageEn code is interpreting this to mean that the values are stored in the TIFF IFD Entry’s Value/Offset bytes (i.e., bytes 8 – 11) when in fact the file offset is stored. This is because TileOffsets and TileByteCounts are special and your code treats them that way in some places, but not all. If you look at your function TIETIFFIFDReader.ReadIFD, you have the following code…
<snip>
// Convert TAGS to LittleEndian (if needed)
if not LittleEndian then
for i := 0 to NumTags - 1 do
begin
if assigned(IFD) then
begin
// classic TIFF
IFD[i].IdTag := IESwapWord(IFD[i].IdTag);
IFD[i].DataType := IESwapWord(IFD[i].DataType);
IFD[i].DataNum := IESwapDWordI( IFD[i].DataNum );
if ( IFD[i].DataNum < 0 ) or
( IFD[i].DataNum > 4 ) or // 11.4.0: Integer overflow catch
( IFD[i].DataNum * IETIFFCalcTagSize(IFD[i].DataType) > 4 ) then
IFD[i].DataPos := IESwapDWord(IFD[i].DataPos); // this is an offset
End
<snip>
Not that this matters since the TIFF data in question is already Little Endian, but this code illustrates that had there been more than 1 tile in the IFD you would have treated the DataPos (or what I referred to as the Value/Offset as a file offset, the comment even says that). And in the case of the data I included, the values in question are offsets, but they aren’t being treated that way. Perhaps your code needs to use the CheckPairTag procedure, or something like it, to identify special tags that are always file offsets and handle them accordingly. I believe this is needed in ReadIFD and likely elsewhere. I think this issue only showed up for me because I have 1 tile and as such the offsets weren't handled as offsets.
In the case of my data above, your TiffHandler application shows TileOffsets as 3 and TileByteCounts as 702 for the first IFD and 7 and 1312236, respectively, for the second IFD. When I click the Show Page for the first IFD it displays an all-black image. The second IFD (page) shows the image but it clearly has a shift in the pixel alignment.
At this time I don’t have an image that I am able to upload to illustrate this issue.
I appreciate any help you can provide to resolve this issue.
Tim F
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TIFF TileOffsets and TileByteCounts problem
Posted - Jun 18 2025 : 18:49:43
