DICOM Standard Browser

C.7.6.3 Image Pixel Module

Note

The use of a value of 4 was previously described, but the Photometric Interpretations that used it have been retired.

Note

Downsampled chrominance planes of a color Photometric Interpretation are a special case, e.g., for a Photometric Interpretation (0028,0004) of YBR_FULL_422. In such cases, Samples per Pixel (0028,0002) describes the nominal number of channels (i.e., 3), and does not reflect that two chrominance samples are shared between four luminance samples. For YBR_FULL_422, Rows (0028,0010) and Columns (0028,0011) describe the size of the luminance plane, not the downsampled chrominance planes.

Defined Terms:

MONOCHROME1

Pixel data represent a single monochrome image plane. The minimum sample value is intended to be displayed as white after any VOI gray scale transformations have been performed. See PS3.4. This value may be used only when Samples per Pixel (0028,0002) has a value of 1. May be used for pixel data in a Native (uncompressed) or Encapsulated (compressed) format; see Section 8.2 in PS3.5 .

MONOCHROME2

Pixel data represent a single monochrome image plane. The minimum sample value is intended to be displayed as black after any VOI gray scale transformations have been performed. See PS3.4. This value may be used only when Samples per Pixel (0028,0002) has a value of 1. May be used for pixel data in a Native (uncompressed) or Encapsulated (compressed) format; see Section 8.2 in PS3.5 .

PALETTE COLOR

Pixel data describe a color image with a single sample per pixel (single image plane). The pixel value is used as an index into each of the Red, Blue, and Green Palette Color Lookup Tables (0028,1101-1103&1201-1203). This value may be used only when Samples per Pixel (0028,0002) has a value of 1. May be used for pixel data in a Native (uncompressed) or Encapsulated (compressed) format; see Section 8.2 in PS3.5 . When the Photometric Interpretation is Palette Color; Red, Blue, and Green Palette Color Lookup Tables shall be present.

RGB

Pixel data represent a color image described by red, green, and blue image planes. The minimum sample value for each color plane represents minimum intensity of the color. This value may be used only when Samples per Pixel (0028,0002) has a value of 3. Planar Configuration (0028,0006) may be 0 or 1. May be used for pixel data in a Native (uncompressed) or Encapsulated (compressed) format; see Section 8.2 in PS3.5 .

HSV

Retired.

ARGB

Retired.

CMYK

Retired.

YBR_FULL

Pixel data represent a color image described by one luminance (Y) and two chrominance planes (CB and CR). This photometric interpretation may be used only when Samples per Pixel (0028,0002) has a value of 3. May be used for pixel data in a Native (uncompressed) or Encapsulated (compressed) format; see Section 8.2 in PS3.5 . Planar Configuration (0028,0006) may be 0 or 1.

This Photometric Interpretation is primarily used with RLE compressed bit streams, for which the Planar Configuration (0028,0006) may be 0 or 1; see Section 8.2.2 in PS3.5 and Section G.2 in PS3.5 . When used in the US Image Module, the Planar Configuration (0028,0006) is required to be 1; see Section C.8.5.6.1.16 “Planar Configuration”.

Black is represented by Y equal to zero. The absence of color is represented by both CB and CR values equal to half full scale.

Note

In the case where Bits Allocated (0028,0100) has value of 8 half full scale is 128.

In the case where Bits Allocated (0028,0100) has a value of 8 then the following equations convert between RGB and YCBCR Photometric Interpretation.

Y = + .2990R + .5870G + .1140B

CB= - .1687R - .3313G + .5000B + 128

CR= + .5000R - .4187G - .0813B + 128

Note

The above is based on CCIR Recommendation 601-2 dated 1990.

YBR_FULL_422

The same as YBR_FULL except that the CB and CR values are sampled horizontally at half the Y rate and as a result there are half as many CB and CR values as Y values.

Planar Configuration (0028,0006) shall be 0. May be used for pixel data in a Native (uncompressed) or Encapsulated (compressed) format; see Section 8.2 in PS3.5 .

Note

1. This Photometric Interpretation is primarily used with JPEG compressed bit streams, but is also occasionally used for pixel data in a Native (uncompressed) format.

2. Though the chrominance channels are downsampled, there are still nominally three channels, hence Samples per Pixel (0028,0002) has a value of 3, not 2. I.e., for pixel data in a Native (uncompressed) format, the Value Length of Pixel Data (7FE0,0010) is not:

   Rows (0028,0010) * Columns (0028,0011) * Number of Frames (0028,0008) * Samples per Pixel (0028,0002) * (⌊(Bits Allocated (0028,0100)-1)/8⌋+1)

   padded to an even length, as it would otherwise be, but rather is:

   Rows (0028,0010) * Columns (0028,0011) * Number of Frames (0028,0008) * 2 * (⌊(Bits Allocated (0028,0100)-1)/8⌋+1)

   padded to an even length.

3. When used to describe JPEG compressed bit streams, the chrominance sub-sampling in the JPEG bit stream may differ from this description. E.g., though many JPEG codecs produce only horizontally sub-sampled chrominance components (4:2:2), some sub-sample vertically as well (4:2:0). Though inaccurate, the use of YBR_FULL_422 to describe both has proven harmless. For a discussion of the sub-sampling notation, see [Poynton 2008].

Two Y values shall be stored followed by one CB and one CR value. The CB and CR values shall be sampled at the location of the first of the two Y values. For each Row of Pixels, the first CB and CR samples shall be at the location of the first Y sample. The next CB and CR samples shall be at the location of the third Y sample etc.

Note

This subsampling sited on the even luminance pixels is often referred to as cosited sampling. The cositing applies when describing pixel data in a Native (uncompressed) form. When used to describe compressed bit streams, the siting depends on the compression scheme. E.g., for JPEG according to JFIF [ISO/IEC 10918-5], the siting is midway between luminance samples, whereas for MPEG2 [ISO/IEC 13818-2], the sampling is cosited with the even luminance pixels. See also [Poynton 2008].

YBR_PARTIAL_422

Retired. See PS3.3-2017b.

YBR_PARTIAL_420

Pixel data represent a color image described by one luminance (Y) and two chrominance planes (CB and CR).

This photometric interpretation may be used only when Samples per Pixel (0028,0002) has a value of 3. The CB and CR values are sampled horizontally and vertically at half the Y rate and as a result there are four times less CB and CR values than Y values.

Planar Configuration (0028,0006) shall be 0. Shall only be used for pixel data in an Encapsulated (compressed) format; see Section 8.2 in PS3.5 .

Note

This Photometric Interpretation is primarily used with MPEG compressed bit streams. For a discussion of the sub-sampling notation and siting, see [Poynton 2008].

Luminance and chrominance values are represented as follows:

1. black corresponds to Y = 16;

2. Y is restricted to 220 levels (i.e., the maximum value is 235);

3. CB and CR each has a minimum value of 16;

4. CB and CR are restricted to 225 levels (i.e., the maximum value is 240);

5. lack of color is represented by CB and CR equal to 128.

In the case where Bits Allocated (0028,0100) has value of 8 then the following equations convert between RGB and YBR_PARTIAL_420 Photometric Interpretation

Y = + .2568R + .5041G + .0979B + 16

CB= - .1482R - .2910G + .4392B + 128

CR= + .4392R - .3678G - .0714B + 128

Note

The above is based on CCIR Recommendation 601-2 dated 1990.

The CB and CR values shall be sampled at the location of the first of the two Y values. For the first Row of Pixels (etc.), the first CB and CR samples shall be at the location of the first Y sample. The next CB and CR samples shall be at the location of the third Y sample etc. The next Rows of Pixels containing CB and CR samples (at the same locations than for the first Row) will be the third etc.

YBR_ICT

Irreversible Color Transformation:

Pixel data represent a color image described by one luminance (Y) and two chrominance planes (CB and CR).

This photometric interpretation may be used only when Samples per Pixel (0028,0002) has a value of 3. Planar Configuration (0028,0006) shall be 0. Shall only be used for pixel data in an Encapsulated (compressed) format; see Section 8.2 in PS3.5 .

Note

This Photometric Interpretation is primarily used with JPEG 2000 compressed bit streams.

Black is represented by Y equal to zero. The absence of color is represented by both CB and CR values equal to zero.

Regardless of the value of Bits Allocated (0028,0100), the following equations convert between RGB and YCBCR Photometric Interpretation.

Y = + .29900R + .58700G + .11400B

CB= - .16875R - .33126G + .50000B

CR= + .50000R - .41869G - .08131B

Note

1. The above is based on [ISO/IEC 15444-1] (JPEG 2000).

2. In a JPEG 2000 bit stream, DC level shifting (used if the untransformed components are unsigned) is applied before forward color transformation, and the transformed components may be signed (unlike in JPEG ISO/IEC 10918-1).

3. In JPEG 2000, spatial down-sampling of the chrominance components, if performed, is signaled in the JPEG 2000 bit stream.

YBR_RCT

Reversible Color Transformation:

Pixel data represent a color image described by one luminance (Y) and two chrominance planes (CB and CR).

This photometric interpretation may be used only when Samples per Pixel (0028,0002) has a value of 3. Planar Configuration (0028,0006) shall be 0. Shall only be used for pixel data in an Encapsulated (compressed) format; see Section 8.2 in PS3.5 .

Note

This Photometric Interpretation is primarily used with JPEG 2000 compressed bit streams.

Black is represented by Y equal to zero. The absence of color is represented by both CB and CR values equal to zero.

Regardless of the value of Bits Allocated (0028,0100), the following equations convert between RGB and YBR_RCT Photometric Interpretation.

Y = ⌊(R + 2G +B) / 4⌋ (Note: ⌊…⌋ mean floor)

CB= B - G

CR= R - G

The following equations convert between YBR_RCT and RGB Photometric Interpretation.

G = Y - ⌊ (CR+ CB) / 4⌋

R = CR+ G

B = CB+ G

Note

1. The above is based on [ISO/IEC 15444-1] (JPEG 2000).

2. In a JPEG 2000 bit stream, DC level shifting (used if the untransformed components are unsigned) is applied before forward color transformation, and the transformed components may be signed (unlike in JPEG ISO/IEC 10918-1).

3. This photometric interpretation is a reversible approximation to the YUV transformation used in PAL and SECAM.

Enumerated Values:

0

The sample values for the first pixel are followed by the sample values for the second pixel, etc. For RGB images, this means the order of the pixel values encoded shall be R1, G1, B1, R2, G2, B2, …, etc.

1

Each color plane shall be encoded contiguously. For RGB images, this means the order of the pixel values encoded is R1, R2, R3, …, G1, G2, G3, …, B1, B2, B3, etc.

Note

Planar Configuration (0028,0006) is not meaningful when a compression Transfer Syntax is used that involves reorganization of sample components in the compressed bit stream. In such cases, since the Attribute is required to be present, then an appropriate value to use may be specified in the description of the Transfer Syntax in PS3.5, though in all likelihood the value of the Attribute will be ignored by the receiving implementation.

Note

In the case of the Supplemental Palette Color LUT, the stored pixel values less than the second descriptor value are grayscale values.

Note

Some implementations have encoded 8 bit entries with 16 bits allocated, padding the high bits; this can be detected by comparing the number of entries specified in the LUT Descriptor with the actual value length of the LUT Data entry. The value length in bytes should equal the number of entries if bits allocated is 8, and be twice as long if bits allocated is 16.

Note

Note

For example, if there are 16 bits per entry specified and only 8 bits of value are truly used then the 8 bit intensities from 0 to 255 must be scaled to the corresponding 16 bit intensities from 0 to 65535. To do this for 8 bit values, simply replicate the value in both the most and least significant bytes.

Figure C.7.6.3.1.7-1. Example of Pixel Size and Aspect Ratio