# Application of Digital Image Analysis for Assessment of Star Content and Distribution in Potatoes
## 2 Materials and Methods  
The experimental materials included 6 potato varieties (Table 1).  
Before the experiment, the potatoes were kept in a cold store at 4 \({}^{\circ}\)C or in a freezer at \(-15\)\({}^{\circ}\)C for 3 months. Each sample was composed of 8 tubers of one variety. At the beginning of the experiment, each tuber was halved: one half was used for a starch content assessment with the polarimetric method developed by [PERSON] and modified by [PERSON], [PERSON], and [PERSON], while the other half was subjected to a digital image analysis with ImageJ software. The polarimetric starch content assessment was repeated thrice for each tuber (3 replications) [20].  
For the digital analysis, each half of a potato was cut into 6 slices of 3 mm thickness and next soaked in 0.5% KI for 1 min to stain the starch granules. Next, the slices were dried on paper and placed on the scanner bed for data acquisition and the digital recording of the image. The image acquisition was conducted for transmitted light: we used overhead lighting with two Diall LED bulbs placed 30 cm above the scanner bed and 15 cm apart from each other emitting neutral white light (4000 K, 1521 lm). Figure 1 shows the spectrum of light emitted by the bulb. The spectrum was measured using the AS7265x sensor.  
\begin{table}
\begin{tabular}{c c c c} \hline
**Variety** & **Culinary Type** & **Flesh Color** & **Origin** \\ \hline Allianz & A (boiling, very early) & white & Piaseczno, Poland \\ Gala & B (all-purpose, early) & pale yellow & Blaszki, Poland \\ Lilly & BC (all-purpose/baking, moderately early) & white & Piaseczno, Poland \\ Lord & AB (boiling/all-purpose, very early) & pale yellow & Piaseczno, Poland \\ Melody & BC (all-purpose/baking, moderately early) & pale yellow & Blaszki, Poland \\ Satina & B (all-purpose, moderately early) & yellow & Germany \\ \hline \end{tabular}
\end{table}
Table 1: Potato varieties used in this study.  
For the digital image analysis, ImageJ software was used ([[https://imagej.nih.gov/ij/](https://imagej.nih.gov/ij/)]([https://imagej.nih.gov/ij/](https://imagej.nih.gov/ij/)), accessed on 10 Dec 2022). Each scan of a potato slice was exported to ImageJ software and transformed into 8-bit greyscale. Next, the range of image brightness was corrected to increase the contrast between the stained and unstained parts of the potato. All the images of potato slices were corrected in an identical way, determined experimentally; the minimum and maximum values of brightness were set at 45 and 130, respectively (Figure 2).  
After the image calibration, histograms of the pixel brightness (Figure 3) were determined along 4 lines crossing at an angle of 45\({}^{\circ}\) (Figure 4C). Next, the results were subjected to statistical analysis using STATISTICA 13 software [21]. The basic statistics of the histogram data were calculated: the mean, median, standard deviation, skewness, and coefficient of variation. Next, the basic statistics were used for a 2-way analysis of variance (ANOVA) to examine the influence of the storage conditions (cold store vs. freezer) and the  
Figure 1: Spectrum of LED bulb.  
potato cultivar. Homogeneous groups were determined by a Duncan test at a significance level of \(\alpha\) = 0.05.  
Figure 4: Scanned potato slice (**A**); image in 8-bit greyscale (**B**); image after contrast correction with determined measurement lines of histograms (**C**).  
Figure 3: Histogram for a single measurement line.