Name: Michelle

Message: My son is doing a science using traditional navajo dyes on churro wool. He is using  photoshop element to find the luminosity of 2oz of wool. He needs to graph the reults but he having a hard time with it. Thanks

What my son did for his project comparing different dyes and different fabrics was, first, to scan his fabric swatches into the computer, using the software that came with our scanner. (It is important to name the brand and model of scanner in the methods section of the report.) Next, he opened each image with Adobe Photoshop Elements 3. Using the 'Rectangular Marquee Tool' (the dotted-line selection box tool), he selected a representative section of the fabric. Under the 'Window' menu, he selected 'Histogram'. On the little window that then appeared, he chose 'Luminosity'. He then wrote down, by hand, in his lab journal, the values that were given for mean, standard deviation, median, and the number of pixels, for each one. The number of pixels (the size of the box when the selection was made of what part of the image to use) should be roughly comparable from one sample to the next. 

It is best to scan the undyed control piece of fabric at the same time as the test sample, even though this means measuring the same piece repeatedly, because sometimes one scan will come out darker than another. Two different sections on the same image are more comparable than two images that were scanned at different times. If several pieces are being compared to one another, it is best to scan them in together, laying them out on the bed of the scanner at the same time.

The maximum possible value for Luminosity in the Photoshop Elements program is 255. The numbers can range from 0 through 255, inclusive. What we care about when we look into the effectiveness of dyes is how dark the fabric is made. This means that the value we are interested in is intensity, rather than luminosity. Therefore, my son subtracted each of his median luminosity values from 255, and used the resulting number for dye intensity. He did the same for his control (undyed) fabric, and subtracted this smaller number from the dye intensity for his dyed fabric. This corrects for the original color of the fabric, which does contribute to the final color. He then divided each one by 255, to yield the percent of maximum possible intensity. If all of the dye being compared were used on the same material, then it is less important to subtract the baseline color intensity of the undyed material.

When my son was ready to make his graphs, he opened a spreadsheet program and entered his numbers into columns. One column listed what each treatment or dye was, and then the next column gave the dye intensity. He used these numbers to get the spreadsheet to make the graphs he needed. (He did not figure out how to add the standard deviation information to his graphs.)

I do not know how closely the numbers obtained by this method approach those one would obtain by other methods. My concern is whether the intensity values obtained in this way will vary linearly with the amount of dye bound to the fiber. However, it does work; it yields numbers which are useful for making graphs, and the equipment required is much more readily available to students than a reflectance spectrophotometer. The numbers produced by this method agree well with subjective judgments made by eye, but are much easier to use for making meaningful graphs summarizing the data. 

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