FI124654B

FI124654B - Measurement of particles in suspension

Info

Publication number: FI124654B
Application number: FI20126359A
Authority: FI
Inventors: Matti-Paavo Sarén
Original assignee: Metso Automation Oy
Priority date: 2012-12-21
Filing date: 2012-12-21
Publication date: 2014-11-28
Also published as: FI20126359A; WO2014096552A1

Description

Measurement of particles in suspension

Field

The invention relates to a measurement of particles in suspension. Background 5 When fibers of pulp are refined, several mechanisms of cell-wall damaging occur. In literature external fibrillation, shortening of fibers, de-lamelation and fibril extraction are reported. There are also damages that are more subtle and cannot be seen easily. The term micro-compression is coined up to describe a local and small-scale compression of a cell wall. It is also pos-10 tulated that micro-compression and curl are linked, although statistically significant data for it is not available. Nevertheless, mechanical properties are linked to these mechanisms. A degree of the micro-compression is important to control because it can be related to quality of paper, for example. However, microcompression cannot be detected with conventional microscopy or image anal-15 ysis, since changes in thickness or length of a cell are too small.

In prior art, fibers have been dyed and images of the dyed fibers have been captured for image analysis. Although dying improves the visibility of the micro-compressions, the quality of the images has not otherwise been good to enough to allow a reliable measurement of degree of micro-20 compression of the fibers. Hence, there is a need for a better solution.

Summary

The following presents a simplified summary of the invention in order to provide a basic understanding of some aspects of the invention. Its pur-? pose is to present some concepts of the invention in a simplified form as a

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™ 25 prelude to the more detailed description that is presented later, o An aspect of the invention relates to apparatus of claim 1.

o An aspect of the invention relates to a method of claim 18.

£ Although the various aspects, embodiments and features of the in- Q- vention are recited independently, it should be appreciated that combinations 30 of the various aspects, embodiments and features of the invention are possible

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™ and within the scope of the present invention as claimed.

° The present solution provides advantages. Good quality images can be captured and particles distinguished. It is also possible to make a reliable measurement of micro-compression of fibers.

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Brief description of the drawings

In the following the invention will be described in greater detail by means of exemplary embodiments with reference to the attached drawings, in which 5 Figure 1 shows an example of an imaging configuration;

Figure 2 shows an example of a measurement chamber;

Figure 3A shows an example of a distance adjustment of the background component;

Figure 3B shows an example of a mechanical variation of reflec-10 tance of an optical background component;

Figure 3C shows an example of a self-radiating background component;

Figure 4 shows an example of a particle with micro-compression zones; 15 Figure 5A presents an example of an intensity distribution of a parti cle in value coordinates;

Figure 5B presents an example of an intensity distribution of a particle in hue coordinates;

Figure 6 presents an example of intensity distribution along an axis 20 of a particle; and

Figure 7 presents an example of a flow chart of the measurement method.

Description of embodiments

Exemplary embodiments of the present invention will now be de- ^ 25 scribed more fully hereinafter with reference to the accompanying drawings, in o which some, but not necessarily all embodiments of the invention are shown.

σ> Indeed, the invention may be embodied in many different forms and should not o ^ be construed as limited to the embodiments set forth herein. Single features of ° different embodiments may also be combined to provide other embodiments.

£ 30 Figure 1 presents a measurement configuration of particles. In the present solution an optical background component 106 directs optical radiation 2 in an adjustable manner to suspension in a measurement chamber 100 from o an opposite direction with respect to optical radiation from a main optical radia-

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tion source 104 illuminating the suspension. An image processor 110 receives 35 images of dyed particles 102 of the suspension having color variation caused 3 by micro-compression from a camera 108 placed on an opposite side of the suspension with respect to the optical background component 106 and form a micro-compression index of the dyed particles on the basis of the color variation of the dyed particles.

5 The particles may be in pulp which is lignocellulosic fibrious solution which may be a result of mechanical and/or chemical processing of wood, recycled paper or the like. Wood fibers and their sections are typical particles in the pulp. Suspension, in turn, may have liquid as medium wherein solid particles such as fibers are dispersed. The particles may also comprise mineral 10 particles in liquid.

Examine now more closely the measurement. A measurement chamber 100 may be a part of a hydraulic circuit 120 where a pump 124 may pump the suspension round the hydraulic circuit 120 and through the measurement chamber 100 such that at different moments different particles 102 15 may be received by the measurement chamber 100.

In an embodiment, the measurement chamber 100 may be coupled to a pulp pipe 126 of a pulp processing mill for receiving an on-line sample of the suspension. A pulp processing mill may be a pulp mill or a paper mill. A pulp mill produces pulp from wood chips or from other plant raw material. The 20 pulp may then be dried into a board form for transportation to further processing. A paper mill uses pulp which it may receive from the pulp mill in order to produce paper or board for consumers. If the outside source is available, it may input new suspension matter to the hydraulic circuit 120 while the measured solution may be flushed back to the pulp duct 126 or it may be drained.

25 Alternatively, a sample of the suspension in the chamber 100 may ^ not circulate but it may still be mixed. After a measurement, the solution may o be flushed back to the pulp duct 126 or it may be drained.

ci) At least a part of the particles 102 are dyed with at least one color o ^ causing color variation to dyed particles on the basis of varying micro- 30 compression. In an embodiment, the dying may be performed in a dying unit £ 130 which may be a part of the hydraulic circuit 120. That enables an on-line measurement. In an embodiment, the dying unit 130 may be separate from the 2 hydraulic circuit 120. In an embodiment, the dying unit 130 may also be sepa- o rate from the measurement chamber 100. The at least one color may comprise

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35 Kongo Red, Nile Blue, Alcian Blue, Sudan, any combination of them or the like.

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They may specifically dye fibers or lignin. Each mineral type may also be dyed in a specific way in order to distinguish it from other minerals.

The coloring may be performed in a coloring chamber 130 before the measurement chamber 100 in the flow direction. The pulp from the pulp 5 duct 126 may be diluted before, after or in the coloring chamber 130 for capturing images. The dyeing of particles in suspension perse is known by a person skilled in the art and that is why it is not explained more.

The measurement configuration of Figure 1 has also a main optical radiation source 104 which illuminates the measurement chamber 100 and the 10 suspension with the particles 102 therein. The optical radiation refers to an electromagnetic radiation the band of which is from 10 nm to 1 mm. A much narrower band about 400 nm to 1200 nm may also be used. Visible region about 400 nm to 700 nm may be possible, too. The optical band in use may be utilized continuously or discretely. The main source 104 of optical radiation 15 may comprise at least one lamp, a wideband light emitting diode (LED) or several leds, a plurality of lasers, their combination or the like.

An optical background component 106 directs optical radiation in an adjustable manner to the measurement chamber 100 from an opposite direction with respect to the optical radiation from the main optical radiation source 20 104. The optical background component 106 is placed on an opposite side of the measurement chamber 100 with respect to the main optical radiation source 104.

A camera 108 may be placed on the same side with respect to the measurement chamber 100 as the main optical radiation source 104. The 25 camera 108 captures images of the dyed particles 102 in the measurement chamber 100. The main optical radiation source 104 may comprise a ring illu-o minator round the camera 108.

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c) The camera 108 may comprise a CCD (Charge-Coupled Device) or o ^ a CMOS (Complementary Metal Oxide Semiconductor) imaging cell (not 30 shown in Figures) which, in turn, may comprise a matrix of detector elements £ such as pixels for detecting optical radiation and for capturing images with the σ> detected optical radiation. The camera 108 may also have at least one optical S element (not shown in Figures) for focusing light coming from the measure- 5 ment chamber 100 to the imaging cell in order to form an image.

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35 The image quality can be controlled such that the optical back ground component 106 is used to adjust the background illumination of the 5 suspension medium to an optimum with respect to the particle 102 illumination coming from the main source 104 of the optical radiation. In this way, the particles 102 can be distinguished in an effective way from the fluid medium without causing too strong or too weak a contrast therebetween. The control also ena-5 bles a good, a desired or the best color separation in each image and for every particle separately. It also may enable a desired resolution in each image and for every particle separately.

An image processer 110 receives the images of the dyed particles 102 and forms a micro-compression index of the dyed particles on the basis of 10 the color variation of the particles 102.

A user interface 112 and a screen 114 may operationally be coupled with the image processor 110 for controlling the image capture, image processing and image presentation, for example.

Figure 2 shows an example of the measurement chamber 100. The 15 measurement chamber 100 may have two plain windows 200, 202 between which the suspension may flow. The windows 200, 202 are transparent to the optical radiation used in the measurement. An optical pass band of the windows 200, 202 may range from about 190 nm to about 1200 nm or even to about 3800 nm, for example. The material of the windows 200, 202 may com-20 prise glass, quartz, sapphire, zinc selenide, germanium, calcium fluoride, or plastic, or the like for example. A distance D of the plain windows 200, 202 may be from hundreds of micrometers to thousands of micrometers. The distance D may be 3 mm, for example. The windows 200, 202 and the edges of the chamber 100 are leak proof and are attached to the rest of the hydraulic 25 circuit 120 in a leak proof manner such that the suspension may not escape out of the measurement chamber 100. The plain surface area of the windows o 200, 202 may vary from a few square millimeters to a few square centimeters, o* for example, o ^ In an embodiment, the optical background component 106 may re- 30 ceive the optical radiation from the main optical radiation source 104 and redi-£ reet the received optical radiation towards the measurement chamber 100.

In an embodiment, the optical background component 106 may re-S ceive the optical radiation through the measurement chamber 100 and redirect 5 said optical radiation back to the measurement chamber 100.

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35 In an embodiment, the optical background component 106 may re ceive the optical radiation of the main source 104 which has travelled around 6 the measurement chamber 100 and redirect said optical radiation to the measurement chamber 100. A part of the optical radiation from the main source 104 may be fed to at least one optical fiber and the optical radiation may be directed from the at least one optical fiber to the optical background component 5 106, for example. A part of the optical radiation from the main source 104 may be reflected using at least one mirror to the optical background component 106 for redirecting it to the measurement chamber 100.

In an embodiment, the optical background component 106 may perform the redirection by reflecting the optical radiation it receives from the main 10 optical radiation source 104 to the measurement chamber 100. The optical background component 106 may reflect the optical radiation travelled through the measurement chamber 100, the optical radiation travelled around the measurement chamber 100 or to both of them.

In an embodiment, the reflective surface of the optical background 15 component 106 may comprise plastic, metal, spectralon or the like. Spectralon provides a very diffuse reflectance from about 250 nm to 2500 nm. Metal and plastic surfaces may be roughened for avoiding a specular reflection.

Figure 3A shows an example of an embodiment, where the intensity of the optical radiation from the optical background component 106 towards 20 the measurement chamber 100 may be adjusted by changing a distance E between the optical background component 106 and the measurement chamber 100. The optical background component 106 may move back and forth with respect to the measurement chamber 100. The movement of the optical background component 106 may be realized by a mover 300 which moves the 25 optical background component 106 mechanically. The movement of the optical ^ background component 106 may be based on a command from the image o processor 110 to the mover 300. The mover 300 may be an electric motor, for g example. The mover 300 may comprise a step motor, a pneumatic cylinder or p!, the like. The farther the optical background component 106 is, the less optical

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30 radiation may direct to the measurement chamber 100. The nearer the optical £ background component 106 is, the more optical radiation may direct to the g measurement chamber 100. The change of distance may be applied to a re- 2 flective and/or self-radiating optical background component 106.

5 In an embodiment, the intensity of the optical radiation of the optical C\l 35 background component 106 directed to the measurement chamber 100 may 7 be adjusted by a change of at least one of the following: the reflection index, refraction index, scattering index, attenuation index.

In an embodiment, a color of the optical background component 106 may change for changing the reflection index.

5 In an embodiment, roughness of a surface of the optical background component 106 may be changed for changing the scattering index. Increased scattering decreases strength of optical radiation reaching the measurement chamber 100.

Figure 3B shows an example of a mechanical implementation for 10 changing either the reflection index or the scattering index. Assume now that different sectors A, B, C and D of a turning disk 302 which represents the optical background component 106 have different reflection indeces and one of the sectors redirect the optical radiation to the measurement chamber 100. By rotating the disk 302, a different reflection index may be selected. The refrac-15 tion index may have a continuous or a discontinuous transition from sector. Without an abrupt change a continuous adjustment may be achieved.

Assume now that different sectors A, B, C and D of a turning disk 302 which represents the optical background component 106 have different scattering indeces and one of the sectors redirect the optical radiation to the 20 measurement chamber 100. By rotating the disk 302, a different reflection index may be selected. The scattering index may have a continuous ora discontinuous transition from sector. Without an abrupt change a continuous adjustment may be achieved.

In an embodiment, the refraction index of a material interacting with 25 the optical radiation may be changed for changing the redirection efficiency.

The change of refraction index may be controlled by a temperature change or o by a change in the electric field strength. The reflection index of a material ok changes when the refraction index changes which may directly be used for the o ^ adjustment. For example, the material interacting with the optical radiation may ° 30 comprise liquid crystal the refraction index of which may be controlled as a £ function of electric field applied to it.

σ> In an embodiment, the background optical component 106 may 2 comprise at least one lens the refractive power of which may be controlled o such that the optical radiation is less effectively converged or collimated to the c\j 35 measurement chamber 100. The variation of the refractive power of the at least one lens may be based on mechanical shape change (corresponding to 8 adaptation of a crystalline lens in the eye) or on variation of electric field, for example. The changes in the reflection index, refraction index, scattering index and/or attenuation index and in the distance between the measurement chamber 100 and the optical background component 106 may also be combined.

5 In an embodiment an example of which is shown in Figure 3C, the optical background component 106 may be self-radiating by generating optical radiation itself. The optical background component 106 may direct the generated optical radiation towards the measurement chamber 100. The optical background component 106 may comprise at least one lamp, led, laser or a 10 similar source 350, 352, 354 for generating optical radiation. Different sources 350, 352, 354 may output the same band or different bands of optical radiation. The redirection of the optical radiation from the main source 104 may be combined with the generation of optical radiation. The optical power of the sources 350, 352, 354 may be separately controlled by electrical power 15 sources 356, 358, 360 under control of the processor 110 for controlling intensity of the background radiation and/or the spectral distribution of the background optical power. A suitable background intensity facilitates color separation. A suitable background spectral distribution also facilitates color separation.

20 In an embodiment, the optical background component 106 may ad just the intensity of the generated optical radiation. The optical output power may be increased by increasing electrical power input to the optical background component 106. The optical output power may be decreased by decreasing electrical power input to the optical background component 106.

25 In an embodiment, the optical background component 106 may ad- just direction of the generated optical radiation to the measurement chamber o 100. The intensity of the optical radiation direction may be increased or deco creased by converging or diverging, respectively, a constant output power of o ^ optical radiation per se to the measurement chamber 100. The divergence and ° 30 convergence may be controlled by changing an optical power at least one lens £ or mirror. The change of optical power may be achieved by moving optically diverging or converging components with respect to each other or by changing 2 refraction index of at least one lens or by changing a reflection index of at least o one mirror.

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35 Figure 4 presents a dyed particle 102 which may be a wood fiber 400 or a section of it. Zones 402 of the fiber 400 may have undergone a micro- 9 compression during a previous process. The micro-compression may be considered as a deformation of a fiber wall or more precisely as a plastic deformation of a fibrillar structure in the fiber wall. That is, at least a portion of the cell wall is compressed during at least one process of pulp such as refin-5 ing.The micro-compression zones 402 can clearly be seen as darker (or lighter) “rings” round the fiber 400 when the fiber is dyed and a proper back illumination by the optical background component 106 is available. Because a degree of micro-compression in fibers of raw material for paper and board manufacturing is typically useful to know, the percentage of micro-compression 10 zones 402 of the total length, area or volume of the fibers 400 may be measured. The micro-compression in fibers may affect a plurality of paper and board parameters which may include mechanical properties such as bending stiffness, strengths, softness, surface structure such as topology, gloss and chemical absorbance etc.

15 The zones 402 of micro-compression have different hue or color than other areas of the fiber. That is why the zones 402 can be observed and spectrally distinguished from the background 404 of the image and other parts of the fiber 400. That the micro-compression zones 402 can be distinguished enables their measurement.

20 A set of images of fibers may be processed in the image processor 110 as follows: 1) a background image with no particles may either be captured or computed; 2) each frame of a measured particle may be linearized and normal- 25 ized; ^ 3) a standard fiber measurement is performed; o 4) a micro-compression index is derived.

ok The step 1) may be performed by computing an average or a medi cs ^ an of a plurality of images with or without particles. The average filters out the 30 effect of particles. The number of images for the background image may be £ hundreds, thousands or even more. A background image may also be formed by capturing only one image or only a few images of the measurement cham-2 ber 100 without any particles.

o The step 2) may be performed by lowering the noise level by filter ed 35 ing. This may be done by dividing a value of each pixel in the image of a parti- 10 ele by a value of a pixel of the measured background. The dividing value may be that of a corresponding background pixel.

The step 3) may refer to length or width of a particle in the image. Additionally, the measurement may cover a determination of deformations of 5 the particle like curl, kink, external fibrillation and lamentation, for example.

The step 4) above may be calculated in several ways. In an embodiment, a spectral analysis of fibers is performed. The image processor 110 may form the micro-compression index on the basis of a ratio of different spectral properties separated by a predetermined threshold in a particle. RGB (Red, 10 Green, Blue) information of fibers may be projected to HVS (Hue value Space) color-space. Variance in color intensity V (Value) or color H (Hue) component may be computed and the micro-compression index may be derived.

In an embodiment, the image processor 110 analyses an image of a particle. Depending on the quality of the image the image processor 110 may 15 control the optical background component 106 to increase the background illumination, keep the background illumination or decrease the background illumination.

In an embodiment, the image processor 110 may control the optical background component 106 to increase the reflectance, may control the optical 20 background component 106 to keep the reflectance or may control the optical background component 106 to decrease the reflectance.

In an embodiment, the image processor 110 may control the optical background component 106 to move closer to the measurement chamber 100, may control the optical background component 106 to remain in its place or 25 may control the optical background component 106 to move farther from the ^ measurement chamber 100.

o In an embodiment, the image processor 110 may control the optical ci) background component 106 to increase the scattering, may control the optical o ^ background component 106 to keep the scattering or may control the optical 30 background component 106 to decrease the scattering.

£ In an embodiment, the quality may be determined on the basis of variation in optical spectral properties of the image of the structure of the parti-2 cle. In an embodiment, the quality may be determined on the basis of variation 5 in spectral properties of the particle. That means, the pixels that represent the C\l 35 particle and not the pixels surrounding the particle may be taken into account. The spectral property may be color, hue or intensity in the pixels belonging to 11 an image of the structure of a particle. In an embodiment, a maximum variation of the spectral property may be searched for.

In an embodiment, the image processor 110 analyses images of a particle each of which are taken with different background illumination. The 5 image processor 110 may then select an image with a suitable quality for the determination of the micro-compression index.

In an embodiment, the image processor may form the microcompression index on the basis of a ratio between two subgroups of spectral property, the two subgroups of the spectral property being formed by associat-10 ing each spectral property with either of the subgroups depending on its value with respect to a predetermined threshold.

Because different sections of each particle are dyed in a different way, it is desirable that the different sections having optical differences could be distinguished from each other as well as possible. A proper illumination 15 presented in this application makes optical differences clear.

Figure 5A shows an example of a measuring method based on the spectral property. The vertical axis is magnitude and the horizontal axis is value which refers here to darkness of the red. In a general case, a darkness i.e. value of any color may be measured. The histogram in Figure 5A has been 20 calculated for image sets having more than 400 images. In Figure 5A, microcompressions 402 can be seen below value from 0.7 which is a threshold between a color of a micro-compression and an area without micro-compression. In an embodiment, the image processor 110 may form the micro-compression index on the basis of a ratio of different color intensities separated by a prede-25 termined threshold in a particle. The micro-compression index may be derived ^ as a ratio of a first area 500 having values 0.6 to 0.75 to a second area 502 o having values 0.75 to 0.90, for example. The areas 500, 502 refer to subgroup ok of magnitudes of pixels separated by a threshold at 0.75 in this example. The o ^ ratio is about 22 % in this example which means that the pulp has fibers 22 % 30 of the total area of which has micro-compression zones.

£ Figure 5B presents another example of a measuring method based on the spectral property. The image processor may form the micro-2 compression index on the basis of a ratio between two subgroups of hue, the o two subgroups of hue being formed by associating each hue with either of the

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35 subgroups depending on its value with respect to a predetermined threshold.

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The example of Figure 5B relates to redness of the particles. The vertical axis means magnitude and the horizontal axis means hue. Also this histogram is calculated for image sets having more than 400 images. At a micro-compressed zone 402, redness turns bluish which means a larger magni-5 tude at a lower value of the hue coordinate. In an embodiment, the image processor may form the micro-compression index on the basis of a ratio of different hues separated by a predetermined threshold in a particle. The microcompression index may be deduced from a ratio of a first area 504 in a range of Hue coordinates 250 to 300 and a second area 506 in a range of Hue coor-10 dinates 340 to 390, for example. The areas 504, 506 refer to subgroup of magnitudes of pixels separated by a threshold at a range of Hue coordinates 300 to 304 in this example.

In an embodiment, spectral analyses along the fibers may be performed. A center line of each fiber may be traced and intensity variations may 15 be interpreted as micro-compressions. A ratio of a total fiber length and a total length of the compressed zones 302 may be formed in order to estimate the micro-compression index. The image processor 110 may thus form the ratio on the basis of pixels’ spectral properties along an axis of a particle. The axis may be a longitudinal axis, for example.

20 Figure 6 shows an example of a curve 602 of the intensity varia tion in this embodiment. The vertical axis denotes intensity in an arbitrary scale and the horizontal axis denotes a distance along a particle in pixels. The line 600 represents a threshold level for deciding whether an intensity value belongs to micro-compression or non-micro-compression. If a pixel’s intensity 25 value in the curve 602 is below the line 600, the image processing unit 110 determines that the value belongs to micro-compression. If a pixel’s intensity o value in the curve 602 is at or above the line 600, the image processing unit c) 110 determines that the value belongs to non-micro-compression. The ratio of o ^ the number of the pixels under the threshold and at or above the threshold rep- ° 30 resent the micro-compression index, micro-compression index = (pixelsun-

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£ der/(pixelsat + pixelsabove), for example.

σ> Figure 7 presents an example of a flow chart of the method. In step S 700, optical radiation is directed, by an optical background component, in an

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5 adjustable manner to suspension from an opposite direction with respect to

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35 optical radiation output by a main optical radiation source illuminating the suspension. In step 702, images of dyed particles of the suspension having color 13 variation caused by micro-compression are received by an image processor from a camera placed on an opposite side with respect to the optical background component. In step 704, a micro-compression index of the dyed particles are formed on the basis of the color variation of the dyed particles by the 5 image processor.

The image processer 110 may comprise a state machine such as at least one computer and at least one suitable computer program. In an embodiment, the device implementing aspects of the invention may be realized as software, or computer program or programs in a processing system.

10 The computer programs may be in source code form, object code form, or in some intermediate form, and it may be stored in some sort of carrier, which may be any entity or device capable of carrying the program. Such carriers include a record medium, computer memory, read-only memory, and software distribution package, for example. Depending on the processing pow-15 er needed, the computer program may be executed in a single electronic digital controller or it may be distributed amongst a number of controllers.

It will be obvious to a person skilled in the art that, as technology advances, the inventive concept can be implemented in various ways. The invention and its embodiments are not limited to the examples described above 20 but may vary within the scope of the claims.

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Claims

1. Apparatus, characterized in that the apparatus comprises an optical background component (106) configured to control the adjustable! optical radiation to the suspension from a direction opposite to optical radiation from the main optical radiation source (104) illuminating the suspension; and an image processor (110) configured to receive images of the suspension colored particles with color variation provided by micro-compression, a camera (108) adjustable to the background optical component (106), and forming the microcompressor particle coefficient of the colored particles color variation.

Apparatus according to claim 1, characterized in that the apparatus further comprises a measuring chamber (100), a main optical radiation source 15 (104) and a camera (108); wherein the measuring chamber (100) is configured to receive a suspension containing pulp particles, wherein at least a portion of the particles is colored with at least one color to effect color variation on the colored particles based on varying microcompression; The main optical radiation source (104) is configured to illuminate the measuring chamber (100), the optical background component (106) is configured to control optical radiation in the measuring chamber (100) from a direction opposite to the optical radiation from the optical radiation source (104); the camera (108) being adjustable relative to the measuring chamber (100) on the same side as the optical radiation source (104) and configured to take images of the colored particles in the measuring chamber (100).

Apparatus according to claim 1, characterized in that the optical background component (106) is configured to receive optical radiation from the optical radiation source (104) and to redirect it towards the measuring chamber (100).

Apparatus according to claim 3, characterized in that: o) the optical background component (106) is configured to adjust the intensity of the directed optical radiation in the measuring chamber m g by at least one of the following: reflection, refractive, scattering, damping. CVJ

Apparatus according to claim 1, characterized in that the optical background component (106) is configured to generate and direct optical radiation towards the measuring chamber (100).

Apparatus according to claim 5, characterized in that the optical background component (106) is configured to adjust the intensity of the directed optical radiation in the measuring chamber (100).

Apparatus according to claim 1, 3 or 5, characterized in that the optical background component (106) is configured to adjust the intensity of the optical radiation by varying the distance between the optical background component (106) and the measuring chamber 10 (100).

Apparatus according to any one of the preceding claims, characterized in that the optical backing component (106) is adjustable on a suspension side opposite to the main optical radiation source (104).

Apparatus according to any one of the preceding claims, characterized in that the apparatus is connected to a pulp tube (126) of a pulp production plant for receiving an in-suspension suspension sample.

Apparatus according to one of claims 2 to 9, characterized in that the measuring chamber (100) is configured to pass a suspension flow.

Apparatus according to any one of the preceding claims, characterized in that the image processor (110) is configured to generate a background image showing the measuring chamber (100) without particles, and to linearize and normalize each image taken from the particle by a background image.

Apparatus according to any one of the preceding claims, characterized in that the image processor (110) is configured to generate a micro-compression coefficient on a peck basis of the variation of the optical property associated with the particles. o

Apparatus according to any one of the preceding claims, characterized in that the image processor (110) is configured to generate a micro compression coefficient on the basis of the ratio between the two subgroups of the spectral property, wherein said two subgroups of the spectral property are depending on its value in relation to a predetermined threshold CVJ 35.

Apparatus according to claim 12, characterized in that the image processor (110) is configured to generate microcompression coefficients based on the relationship between the two subgroups of the hue, wherein said two subgroups of the hue are formed by assigning each hue to either of said subgroups. threshold.

Apparatus according to claim 12, characterized in that the image processor (110) is configured to generate microcompression coefficients based on the relationship between the two subgroups of color intensities associated with the at least one particle, said two intensities being formed by separating the color intensities into two subgroups.

Apparatus according to claim 12, characterized in that the image processor (110) is configured to form a ratio based on the optical properties of the pixels 15 along the longitudinal axis of the particle.

Apparatus according to claim 1, characterized in that the image processor (110) comprises: at least one processor; and at least one memory including computer program code, wherein said at least one memory with said at least one processor and computer program code is configured to cause the processing device to generate a microcompression coefficient of the colored particles based on the color variation of the particles.

A method for measuring, characterized in that method 25 controls (700) the optical radiation component (106) to adjust the optical radiation! the suspension from a direction opposite to the optical radiation ci) emitted by the main optical radiation (104) illuminating the suspension o; and? receiving (702) with the image processor (110) images of dyed particles contained in the suspension having a color variation obtained by microcompression from a camera (108) set on an optical background (106). ) on the opposite side of the relationship; and 2 is formed (704) by microcompression coefficients of the colored particles on the basis of the color variation of the colored particles by the image processor (110). CVJ

A method according to claim 18, characterized in that the method comprises receiving a suspension containing mass particles in the measuring chamber (100), wherein at least a part of the particles is colored with at least one color to effect color variation on the colored particles by varying microcompression; 5 illuminates the measuring chamber (100) with the main optical radiation source (104), the optical radiation component (106) controls the optical radiation to be adjusted! a measuring chamber (100) from a direction opposite to the optical radiation from the optical radiation source (104). 10 't δ c \ j O) o CO o X cc CL CD LO CO CO C \ l δ CM