Apply Modality LUT on Encapsulated Format encoding

[Anand]

How to apply modality lut & voi lut to encapsulated pixel format?
Please help
I have a JPEG-LS Lossless transfer syntax CT dcm image which has
bits allocated 16
bits stored = 12
high bit = 11
rows = 512
columns = 512

DICOM PS 3.5 states "The use of the DICOM Encapsulated Format to
support JPEG Compressed Pixel Data requires that the
Data Elements that are related to the Pixel Data encoding (e.g.
Photometric Interpretation, Samples per Pixel, Planar Configuration,
Bits Allocated, Bits Stored, High Bit, Pixel Representation, Rows,
Columns,etc.) shall contain values that are consistent with the
characteristics of the compressed data stream. The Pixel Data
characteristics included in the JPEG Interchange Format shall be used
to decode the compressed data stream."

Considering the bits allocated, rows & columns as characteristics of
compressed pixel data , (0x7FE0,0x0010) length should be
(rows*columns*bitsAllocated)/8 bytes = 524288 bytes, however this
does not yield compression!

Please explain how can i use bits allocated, bits stored, rows columns
& other pixel data related DICOM elements.

Thanks in adance for your help!

[David Clunie]

Hi Anand

When the bitstream is compressed, it will (usually) be shorter than
the number of uncompressed bytes that would otherwise be sent.

What this section of PS 3.5 is trying to say is that if the compressed
bit stream contains information about, for example, the number of rows
and columns, then those will not be inconsistent with the values in the
DICOM attributes; e.g., if a compressed JPEG bitstream marker segment
says 512 columns, then the corresponding DICOM attribute should have
exactly the same value.

Note sure what this has to do with the Modality and VOI LUT mentioned
in the subject line, other than to say that once you get the decompressed
pixel data values out of the decompressor, you need to interpret those
as per the Image Pixel Module attributes, e.g., to determine whether the
16 bit pixel data words are signed or unsigned, you need to look at
Pixel Representation (particularly if the compression scheme does not
support the concept of signed values, e.g., in JPEG 10918-1 lossless),
and mask unused high bits and possibly sign extend into them, etc.

David

PS. One would expect the the number of decompressed bytes (not compressed)
bytes to equal:

frames * rows * columns * ((bitsAllocated-1)/8)+1)

NB. take care of the length of the integer word when doing this
calculation for large objects.

On 2/7/12 10:37 AM, Anand wrote:
> How to apply modality lut& voi lut to encapsulated pixel format?

> Please help
> I have a JPEG-LS Lossless transfer syntax CT dcm image which has
> bits allocated 16
> bits stored = 12
> high bit = 11
> rows = 512
> columns = 512
>
> DICOM PS 3.5 states "The use of the DICOM Encapsulated Format to
> support JPEG Compressed Pixel Data requires that the
> Data Elements that are related to the Pixel Data encoding (e.g.
> Photometric Interpretation, Samples per Pixel, Planar Configuration,
> Bits Allocated, Bits Stored, High Bit, Pixel Representation, Rows,
> Columns,etc.) shall contain values that are consistent with the
> characteristics of the compressed data stream. The Pixel Data
> characteristics included in the JPEG Interchange Format shall be used
> to decode the compressed data stream."
>

> Considering the bits allocated, rows& columns as characteristics of

[Anand]

Thanks David, this is very helpful, what I understand is as follows
STEP 1. Read the pixel data from 7FE0,0010 which is in compressed
pixel format (JPEG LOSSLESS TS)
STEP 2. Apply Decompression to pixel data
STEP 3. Process Bits Allocates, Bits Stored & High Bit (Mask the
unused bits)
STEP 4. Apply the Modality LUT Processing on the Pixel Sample Value
obtained from STEP 3
Step 5. Apply VOI LUT & Presentation LUT
Step 6. Image is ready for display

Please correct me if I am wrong!

Thanks again for your help.

Regards,
Anand