Article pp.120-123 du Vol.23 n°1 (2003)

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120-123 Sci. Aliments 23(1), 2003 P. Marty-Mahé et al.

FOCUS : JSMTV

Study of tissues mapping and flesh quality of brown trout by color image analysis

P. Marty-Mahé¹, P. Loise¹, B. Fauconneau², P. Haffray³, D. Brossard¹

ABSTRACT

With the Trade Union of the French Poultry and Aquacole Selectors (SYSAAF) and French National Institute of Agronomical Research (INRA) we studied the farmed brown sea-trout development according to genetic improvement and feeding composition by color image analysis. They want to value the effects of feeding which contains various levels of lipid.

In this research project a vision system was devised to research and measure brown trout visual features. Various segmentation methods were applied to locate various tissues of brown trout cutlets and to measure their area and color. The results obtained on fish flesh by the image analysis were compared with chemical measurements of fat and with NMR measurements.

The color image features provide data on the development of various tissues and the effect of feeding on morphological development can be tested on efficient aspect variables.

Keywords:

Vision, color images, segmentation, quality control, sea-trout, fat, color muscles.

1 – INTRODUCTION

The Trade Union of the French Poultry and Aquacole Selectors (SYSAAF) and National Institute of Agronomical Research (INRA) study the farmed brown sea-trout development according to genetic improvement and diet composition

1. Équipe PAIC URE TERE Cemagref , 17, avenue de Cucillé, CS 64427, 35044 Rennes Cedex, pas- cale.marty-mahe@cemagref.fr, phone : 02 23 48 21 21, fax : 02 23 48 21 15.

2. INRA, Station SCRIBE Campus de Beaulieu ,35042 Rennes Cedex.

3. SYSAAF Station SCRIBE Campus de Beaulieu, 35042 Rennes Cedex.

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Study of tissues mapping and flesh quality of brown trout by color image analysis 121

and quality control. They want to assess the effects of the genetic modifications and the selection on the fish flesh quality and fish aptitude for the transforma- tion. They want to value the effects of feeding which contains various rates of lipid.

They have asked Cemagref to develop two new tools based on MRI and Color image analysis, to know the fat content, distribution in the various tissues and color distribution in the different parts of fish flesh and in various muscles.

A color image system was devised to research and measure brown trout visual features, according to genetic characteristics and feeding composition of trouts sets. A color vision system was developped and calibrated to grab color image and segmentation methods were applied to locate various tissues of fario trout cutlets and to measure their area and color. The results obtained on fish flesh by the image analysis were compared to chemical levels of fat by Soxlet method and by NMR measurements. The color image features give data on the development of various tissues and the effect of feeding on morphological development can be tested on efficient aspect variables.

2 – MATERIALS AND METHODS

2.1 Animals

The experiment was performed on 48 27-month-old brown trouts from 2 genotypes, a control line and an improved population . Fish were fed two different diets with 16% (low Fat Regime LFR) or 26% (High Fat Regime HFR) of lipids during their 4 last months of growth in cages in sea water at the SEMII (Salmoniculture Expérimentale Marine IFREMER-INRA) Camaret (France). Trout feed was pigmented with 40 ppm astaxanthin during the last 12 months of sea rearing. At slaughtering, fish were bled to death in ice cold water and transported to Cemagref laboratory where measuring were performed 48 h after slaughtering. Cutlets were cut from each fish and 6 of them were studied per fish.

2.2 Color Vision System

A color vision system was devised and calibrated to study sea-trout cutlets following a specific experimental protocol. In order to get high quality images, a diffuse and uniform lighting was devised to avoid specular reflection on sea- trout cutlets images. A tri CCD DXC 930 P SONY camera and an acquisition and digitization EDX 512 C (EDIXIA) board were used to obtain RGB images on 3*7 bits. A color calibration process was applied to compute L*a*b* images which are comparable between various acquisitions and experimentations. A uniform grey background and Macbeth color patch images were used to cor- rect lighting defects and to calculate XYZ images and a XYZ - L*a*b* transfor- mation was performed.

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122 Sci. Aliments 23(1), 2003 P. Marty-Mahé et al.

2.3 Image Processing

Color image treatments were applied to extract various morphological parts of the cutlets. Various segmentation methods were applied on various colorime- tric components to extract fish flesh, myoseptes, the red muscle, peripheral fat, the background and skin components (Fig 1).

Figure 1

Results of tissues segmentation

2.4 Measurements

The color of the fish flesh was measured, with and without the myoseptes , in the CIELAB color space. These color measurements were made on the whole cutlets. The areas of the myoseptes, of the red muscle and the fat peripheral components were measured.

3 – RESULTS

The feeding had a significant effect on L* of flesh, fish fed with HFR being lighter, but had no significant effect on a* and on b*. The feeding has also a significant effect on areas of myoseptes segmented and on areas of red muscles and peripheral tissues. The selection has no significant on effect vision features.

The lipid level of fish flesh was measured by chemical method and by NMR (Toussaint et al. 2002). Numerical models to predict lipid level of fish flesh with various color image features (L*, color features, areas of myoseptes, areas of red muscles, areas of peripheral tissues...) were studied. The best monodimen-

Myoseptes segmentation Red muscle and peripheral fat segmentation

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Study of tissues mapping and flesh quality of brown trout by color image analysis 123

sional linear regression was obtained with L*. The best twodimensional linear regression was obtained with L* and C*. L*, C* and areas of myoseptes gave the best threedimensional regression.

4 – DISCUSSION AND CONCLUSION

L* of fish flesh decrease with the lipid level of diet. The anterior-posterior L*, a* and b* gradients were observed. The myosepte segmentation methods were interesting but not perfect because of the size of pixels (0.3 mm * 0.4 mm), but the results showed the effect of lipid level of diet on myoseptes development.

The results also showed the influence of feed quality on the development of red muscle and peripheral tissues. Rich in oxidative lipids these tissues often cause problems for processors and smokers.

In the color components of fish flesh L* is the best predictor of lipid level in the muscle. The accuracy is interesting to sort trouts but not very important to give an accurate lipid level.

This study showed that an image analysis system can provide preliminary features for future application in processing houses.

The method was also succinctly tested on other kind of fish.

REFERENCES

TOUSSAINT C.A., MÉDALE F., DAVENEL A., AKOKA S., HAFFRAY P., FAUCONNEAU B., 2002. Determination of the lipid content in fish muscle by a self-calibrated

NMR relaxometry method: Comparison with classical chemical extraction methods. J. Sci. Food Agric., 82, (2), 173-178.