class_docstr: Class for Cifti2 header extension
class_docstr_tok: ["Class","for","Cifti2","header","extension"]
code: def _chk_pixdims(hdr, fix=False):
      rep = Report(HeaderDataError)
      pixdims = hdr["pixdim"]
      spat_dims = pixdims[1:4]
      if not np.any(spat_dims < 0):
          return hdr, rep
      rep.problem_level = 35
      rep.problem_msg = "pixdim[1,2,3] should be zero or positive"
      if fix:
          hdr["pixdim"][1:4] = np.abs(spat_dims)
          rep.fix_msg = "setting to abs of pixdim values"
      return hdr, rep
  
imports: from io import BytesIO
  import numpy
  from packaging.version import Version, parse
  from ..None import xmlutils
  from ..batteryrunners import Report
  from ..nifti1 import Nifti1Extension, extension_codes, intent_codes
  from ..nifti2 import Nifti2Header, Nifti2Image
  from ..spatialimages import HeaderDataError
  from .cifti2 import CIFTI_BRAIN_STRUCTURES, CIFTI_MODEL_TYPES, Cifti2BrainModel, Cifti2Header, Cifti2HeaderError, Cifti2Label, Cifti2LabelTable, Cifti2Matrix, Cifti2MatrixIndicesMap, Cifti2MetaData, Cifti2NamedMap, Cifti2Parcel, Cifti2Surface, Cifti2TransformationMatrixVoxelIndicesIJKtoXYZ, Cifti2VertexIndices, Cifti2Vertices, Cifti2Volume, Cifti2VoxelIndicesIJK, _underscore
label_desc: Use image node_id 4 for calling the _Cifti2AsNiftiHeader obj's underlying member method code with example usage: obj._chk_pixdims(hdr, fix) and returns: hdr,  rep, hdr,  rep