JPH0685565B2 - X-ray film image reading method - Google Patents

Description

TECHNICAL FIELD The present invention relates to an X-ray film image reading method in an X-ray film image reading apparatus for reading an X-ray film image and obtaining information contained therein.

(Prior Art) Conventionally, as a device for reading information included in an X-ray film image, an X-ray film is irradiated by a light source, and the light transmitted through the film is transmitted through an optical system such as a solid-state imaging device such as CCD (charge coupled device) or There is known a device that obtains an image signal by converting document information into an electric signal by guiding it to a photoelectric conversion element such as a diode array. In a conventional X-ray film reading device, the conversion process of the read image is represented by the transmittance. Since the image signal is fixed to either linear conversion or logarithmic conversion, when reading X-ray film over a wide range of image density with the same device, effective information with high resolution cannot be obtained for all images. There's a problem.

(Object and Structure of the Invention) The present invention has been made in view of the above points, and an object thereof is to obtain effective information in accordance with the density of a film image. ,
X because the density of the entire image is low due to the
When scanning a line film or a part with low image density, high resolution information can be obtained by linearizing the image signal representing the film transmittance and then digitizing it, while the density of the entire image is high. When reading an area with high density, focusing on the fact that effective information with high resolution can be obtained by digitizing the image signal representing the transmittance of the film after logarithmic conversion, and the amount of transmitted light of the image area of the X-ray film to be observed. A transmittance linear conversion means for linearly converting the image signal obtained by photoelectrically converting the image and a density linear conversion means for logarithmic conversion are provided, and either one of the conversion means is selected according to the density of the image region. Configured.

(Example) The present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of an X-ray film image reading apparatus according to the present invention. Reference numeral 1 denotes an X-ray film scanned with a laser beam and the transmitted light thereof is received by a photomultiplier to obtain an image signal. The image reading means 2 and 3 for outputting are relays for switching the conversion processing of the image signal between the density linear conversion and the transmittance linear conversion according to the density of the image to be observed, and the contact 2a for switching between a and b. , 3a and coil 2
It consists of b and 3b. Reference numeral 4 linearly amplifies the weak image signal output from the image reading means 1 (transmissivity linear conversion).
A current amplifier, 5 is a logarithmic amplifier for logarithmically converting and amplifying a weak image signal (density linear conversion), 6 is an A / D converter, 7
Is a manual switch for switching the conversion processing of the image signal according to the image density. When the switch is turned on, the density linear conversion processing is performed, and when it is turned off, the transmittance niria conversion processing is performed. FIG. 2 shows a density linear conversion characteristic A (solid line) obtained by linear conversion and a density linear conversion characteristic B (broken line) obtained by logarithmic conversion when the amount of transmitted light of the X-ray film is photoelectrically converted. The range up to is shown with 10-bit gradation. In this figure, the vertical axis represents the density resolution, that is, the density difference per step when digitized (quantized).

In the case of density linear conversion, if the range of density 4 is divided into 1024, the density difference per step is 0.0039D in any density range, but in the case of transmittance linear conversion, the amount of transmitted light is divided into 1024. As a result, only a maximum of 3.01D can be captured, and the density difference per step varies depending on the density range. For example, in the density 1 area, the density difference per step is about 0.004D,
It becomes 0.045D in the density 2 area.

From this, if the image density or the density of the image part you want to observe is as low as 1.0 or less, you can obtain information in fine density steps by reading in the transmittance linear conversion mode. It is understood that when is higher than that, information can be obtained in fine density steps by reading in the density linear conversion mode.

Now, returning to FIG. 1, the operation of the reading apparatus according to the present invention will be described. The operator visually judges whether the density of the entire image of the X-ray film to be observed or the density of the image portion to be observed is low or high, and it is low. In this case, turn off the manual switch. As a result, the image signal read and output by the image reading means 1 is linearly converted by the current amplifier 4 into the transmittance, and then digitally converted by the A / D converter 6 and sent to the storage or processing circuit in the subsequent stage. In this way, effective read information is obtained.

On the other hand, when it is determined that the density of the image to be observed is high, the manual switch 7 is turned on. As a result, the coils 2b and 3b of the relays 2 and 3 are energized, the contacts 2a and 3a are switched from a to b, and the image reading means 1
The image signal output from is amplified by a logarithmic amplifier 5 and subjected to density linear conversion, is digitally converted by an A / D converter 6, and is sent to a storage or processing circuit in a subsequent stage. Effective read information is thus obtained for high image densities.

In the above embodiment, the switch 7 is manually switched, but the average density of the image is automatically judged prior to image reading, and the switch 7 is turned on or off based on the result.
You may make it switch F automatically.

The present invention is not particularly limited with respect to image reading of an X-ray film, and in addition to using laser light and a photomultiplier as in the embodiment, irradiating the X-ray film with a fluorescent lamp,
It goes without saying that a reading method in which the transmitted light is received by a CCD may be used.

(Effects of the Invention) As described above, in the present invention, an image signal obtained by photoelectrically converting the amount of transmitted light of a portion of an X-ray film image to be observed is subjected to logarithmic conversion with transmittance linear conversion means for linear conversion. Since the density linear conversion means is provided and either one of the conversion means is selected according to the density of the image portion, it is possible to always read effective information for an X-ray film image in a wide density range. Therefore, the usability as a reading device is improved.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of the X-ray image reading apparatus according to the present invention, and FIG. 2 is a diagram showing the relationship between the film density and the density difference per step when digitized. 1 ... Image reading means, 2, 3 ... Relay, 4 ... Current amplifier, 5 ... Logarithmic amplifier, 6 ... A / D converter, 7 ... Manual switch

Claims (1)

[Claims] 1. An image signal is linearly converted and read as a mode in which information of an X-ray film image is read from an image signal obtained by irradiating an X-ray film image with light and photoelectrically converting transmitted light of the X-ray film. X equipped with a transmittance linear mode and a density linear conversion mode in which an image signal is logarithmically converted and read.
In the linear film image reading device, the transmittance linear mode is selected when the image density is less than a predetermined value, and the density linear conversion mode is selected when the image density exceeds the predetermined value. Characteristic X-ray film image reading method.