了解DICOM图像中的BPP [英] Understanding the BPP inside DICOM images

问题描述

几天以来，我一直在使用FO-DICOM处理DICOM文件。

I'm working with DICOM files since a few days, using FO-DICOM.

我正在使用一组dicom文件进行测试，而我一直在打印光度学解释和每像素样本值，以更好地了解我正在处理哪种类型的图像。

I'm using a set of dicom files for my tests, and I've been printing the "Photometric Interpretation" and the "Sample Per Pixel" values, to have a better understanding of what kind of images I'm working with.

结果是，光度解释为 MONOCHROME2，每像素样本为 1。

The result was "MONOCHROME2" for the Photometric Interpretation, and "1" for the Sample Per Pixel.

通过阅读标准的第3部分，我了解到MONOCHROME2代表一个灰度，从黑色开始为其最小值。

What I understood by reading the part3 of the standard is that MONOCHROME2 represent a gray scale, starting from black for its minimum values.

但是，每像素采样数到底是多少？我以为这代表了每个像素的字节（而不是位数）的数量（逻辑上，每像素有8个 bits 可以显示灰度等级吗？）

But what is the Sample Per Pixel exactly? I thought this was representing the number of bytes (and not bits) per pixel (that would be logic to have 8 bits per pixel for a scale of gray right?)

但是我的问题是实际上我的图像似乎有32 bpp。
我正在处理512 * 512像素的图像，并将其转换为字节数组。所以我期待的是512 * 512 = 262144字节的数组。
但是我得到了1048630字节的数组（比4 * 262144多一点）

But my problem here is that actually, my images seem to have 32 bpp. I'm working with 512*512 pixels images, and I converted them into byte arrays. So I was expecting arrays of 512*512=262144 bytes. But I get arrays of 1048630 bytes (which is a bit more than 4*262144)

有人有解释吗？

编辑：

以下是我的一些数据：

PhotometricInterpretation=MONOCHROME2
SamplePerPixel=1
BitsAllocated=16
BitsStored=12
HighBit=11
PixelRepresentation=0
NumberOfFrames=0

推荐答案

属性（ 0028,0002） SamplesPerPixel 仅指彩色图像，并告诉您图像中存在的平面数（例如RGB为3），因此您有

The attribute (0028,0002) SamplesPerPixel refers to color images only and tells you the number of planes which are present in the image (e.g. 3 for RGB), so you have

PhotometricInterpretation=RGB
SamplesPerPixel=3

每个像素有8位（我将在下面重新访问BPP）。只要您具有 PhotometricInterpretation = MONOCHROME1或MONOCHROME2，您就可以期望 SamplesPerPixel 为1。

With 8 bits per pixel (I will revisit BPP below). As long as you have PhotometricInterpretation = MONOCHROME1 or MONOCHROME2, you can expect the SamplesPerPixel to be 1 and nothing else.

您必须考虑的是每个像素的位数：

What you do have to take into consideration is the number of bits per pixel:

BitsAllocated (0028,0100)
BitsStored (0028,0101)
HighBit (0028,0102)

这些告诉您使用多少位来编码像素值（ BitsAllocated ），以及其中哪些位真正包含灰度信息（ BitsStored ， HighBit ）。 HighBit 从零开始，通常但不一定= BitsStored-1

These tell you how many bits are used to encode a pixel value (BitsAllocated) and which of these bits really contain grayscale information (BitsStored, HighBit). HighBit is zero-based and usually but not necessarily = BitsStored-1

一个例子来说明这一点：对于CT图像，通常以hounsfield单位表示灰度值，范围从-1000到+3000。这些由以2字节对齐方式存储的12位表示，因此

An example to illustrate this: For CT images, it is very common to express gray values in hounsfield units which range from -1000 to +3000. These are represented by 12 bits which are stored with a 2-byte-alignment, so

BitsAllocated (0028,0100) = 16
BitsStored (0028,0101) = 12
HighBit (0028,0102) = 11

另一个自由度是 PixelRepresentation ，它告诉您像素数据是编码为无符号（0）还是2s补码（1）。我都看过CT图像，但是对于除CT以外的其他图像类型，带符号的像素数据非常少见。

Another degree of freedom is PixelRepresentation which tells you if the pixel data is encoded unsigned (0) or in 2s complement (1). I have seen both for CT images, however signed pixel data is rather unusual for image types other than CT.

在您的示例中，我假设分配的位== 32或（不太可能）您的数据集包含多个图像（帧），因此 NumberOfFrames（0028,0008）>1。如果没有帧数，您可以放心地假设只有一帧。

In your example, I would assume that Bits Allocated == 32 or (not very likely) that you have a dataset containing multiple images ('frames'), so NumberOfFrames (0028,0008) > 1. If Number of Frames is absent, you can safely assume to have only one frame.

我在这里稍微简化了一点，尤其是关于彩色图像，但是我认为这已经足够复杂了；-)。基本上，DICOM可以提供任何可想像的自由度来编码像素数据并在标头中描述编码。

I have over-simplified a bit here, especially about color images but I think this is complicated enough ;-). Basically, DICOM offers any thinkable degree of freedom to encode pixel data and describe the encoding in the header.

我想我建议您看一下DCMTK中的内容。最近的帖子。 DicomImage类具有一个不错的接口（ getInterData（）），该接口关心所有内容，并以规范化格式提供从DICOM文件读取的像素数据。

I think I have recommended you to have a look at the DCMTK in a recent post. The DicomImage class features a nice interface (getInterData()) which cares about all that stuff and provides the pixel data read from a DICOM file in a normalized format.

：随时在此处发布数据集的DICOM转储，我将对其进行介绍并告诉您如何解释像素数据。

: Feel free to post a DICOM dump of your dataset here, I would have a look at it and tell you how to interpret the pixel data.

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