DICOM: fix width of values with DS VR

[melissalinkert]

Fixes #4376.

With this change, bfconvert -noflat -compression JPEG CMU-1.ndpi CMU-1.dcm or similar and then dcdump CMU-1_0_0.dcm should show:

...
  > (0x0028,0x0030) DS Pixel Spacing 	 VR=<DS>   VL=<0x0022>  <0.00045641259698\0.00045506257110 > 
...

In addition to the issue noted in #4376, this checks other values of type DS to make sure the width is correct. I don't necessarily like the current implementation of formatFixedWidth, so definitely open to better ideas for how to turn a double into a string of no more than n characters total. DecimalFormat and String.format(...) can easily give a string with at least n characters, or with a fixed precision, but I couldn't find a good concise way to guarantee no more than n characters.

For Pixel Spacing, the fixed width is set to 15 so that even if the padding space were included, the value will still have no more than 16 characters.

[fedorov]

...
  > (0x0028,0x0030) DS Pixel Spacing 	 VR=<DS>   VL=<0x0022>  <0.00045641259698\0.00045506257110 > 
...

Why not use scientific notation?

[fedorov]

Here's somewhat related issue, just for the reference - we went quite a bit back and forth on how to ensure best use of the limited character length: QIICR/dcmqi#414 (that code is C++).

[dclunie]

... I couldn't find a good concise way to guarantee no more than n characters.

You may want to look at my Java code, which handles a bunch of fringe conditions to try to maximize the preserved precision, in this method https://www.dclunie.com/pixelmed/software/javadoc/com/pixelmed/utils/FloatFormatter.html#toStringOfFixedMaximumLength-double-int-boolean-java.util.Locale-

The class source is attached for your convenience:

FloatFormatter.java

[fedorov]

Here's that function in a GitHub repo where I synchronize @dclunie pixelmed, for convenience:

https://github.com/fedorov/pixelmed/blob/f9b7844749f15fd8d6523d119f4c3792738c40a3/com/pixelmed/utils/FloatFormatter.java#L105-L227

[sbesson]

I was able to reproduce the issue using Bio-Formats 8.4.0 and CMU-1.npi and the dicom3tools utility

sbesson@Sebastien-GS-MacBook-Pro-2025 Downloads % BF_CP=libjpeg-turbo-java-0.1.0-SNAPSHOT.jar ./bftools/bfconvert -noflat -precompressed CMU-1.ndpi CMU-1.dcm  
CMU-1.ndpi
NDPIReader initializing CMU-1.ndpi
Reading IFDs
Populating metadata
Populating OME metadata
Implicitly using compression = JPEG
[Hamamatsu NDPI] -> CMU-1.dcm [DICOM]
More than 4GB of pixel data, compression will need to be used
Tile size = 2048 x 512
	Series 0: converted 1/1 planes (100%)
Tile size = 512 x 512
	Series 0: converted 1/1 planes (100%)
Tile size = 128 x 128
	Series 0: converted 1/1 planes (100%)
Tile size = 800 x 596
	Series 0: converted 1/1 planes (100%)
Tile size = 1191 x 408
	Series 1: converted 1/1 planes (100%)
[done]
22.121s elapsed (1.8+4146.6ms per plane, 711ms overhead)
sbesson@Sebastien-GS-MacBook-Pro-2025 Downloads % ./dicom3tools_macexe_1.00.snapshot.20250715101647/dciodvfy CMU-1_0_0.dcm 
Warning - NumberOfFrames does not match expected value for tiled total pixel matrix got 23.3683 expected 23.2992 for 51200 columns, 0.000455063 PixelSpacing between columns
Warning - NumberOfFrames does not match expected value for tiled total pixel matrix got 17.3579 expected 17.4094 for 38144 rows, 0.000456413 PixelSpacing between rows
Warning - Missing attribute or value that would be needed to build DICOMDIR - Patient ID
Warning - Missing attribute or value that would be needed to build DICOMDIR - Study Date
Warning - Missing attribute or value that would be needed to build DICOMDIR - Study Time
Warning - Missing attribute or value that would be needed to build DICOMDIR - Study ID
Error - Value invalid for this VR - (0x0028,0x0030) DS Pixel Spacing  DS [1] = <4.564125969876768E-4> - Length invalid for this VR = 20, expected <= 16
Error - Value invalid for this VR - (0x0028,0x0030) DS Pixel Spacing  DS [2] = <4.550625711035267E-4> - Length invalid for this VR = 20, expected <= 16
Error - Dicom dataset contains invalid data values for Value Representations
VLWholeSlideMicroscopyImage

With this change included, the same conversion yields no Error when running dcdump

sbesson@Sebastien-GS-MacBook-Pro-2025 Downloads % BF_CP=libjpeg-turbo-java-0.1.0-SNAPSHOT.jar ~/Documents/GitHub/bioformats/tools/bfconvert -noflat -precompressed CMU-1.ndpi CMU-1.dcm 
CMU-1.ndpi
NDPIReader initializing CMU-1.ndpi
Reading IFDs
Populating metadata
Populating OME metadata
Implicitly using compression = JPEG
[Hamamatsu NDPI] -> CMU-1.dcm [DICOM]
More than 4GB of pixel data, compression will need to be used
Tile size = 2048 x 512
	Series 0: converted 1/1 planes (100%)
Tile size = 512 x 512
	Series 0: converted 1/1 planes (100%)
Tile size = 128 x 128
	Series 0: converted 1/1 planes (100%)
Tile size = 800 x 596
	Series 0: converted 1/1 planes (100%)
Tile size = 1191 x 408
	Series 1: converted 1/1 planes (100%)
[done]
18.958s elapsed (1.4+3613.4ms per plane, 509ms overhead)
sbesson@Sebastien-GS-MacBook-Pro-2025 Downloads % ./dicom3tools_macexe_1.00.snapshot.20250715101647/dciodvfy CMU-1_0_0.dcm 
Warning - NumberOfFrames does not match expected value for tiled total pixel matrix got 23.3683 expected 23.2992 for 51200 columns, 0.000455063 PixelSpacing between columns
Warning - NumberOfFrames does not match expected value for tiled total pixel matrix got 17.3579 expected 17.4094 for 38144 rows, 0.000456413 PixelSpacing between rows
Warning - Missing attribute or value that would be needed to build DICOMDIR - Patient ID
Warning - Missing attribute or value that would be needed to build DICOMDIR - Study Date
Warning - Missing attribute or value that would be needed to build DICOMDIR - Study Time
Warning - Missing attribute or value that would be needed to build DICOMDIR - Study ID
VLWholeSlideMicroscopyImage

and the output of dcdump CMU-1_0_0.dcm shows

    > (0x0028,0x0030) DS Pixel Spacing 	 VR=<DS>   VL=<0x001e>  <.00045641259699\.0004550625711> 

The float formatting API and the associated unit tests are consistent with the implementation suggested in the review and should protect against future regressions.