Too many numbers

[ColinRH]

When looking to take density readings from a scanned alternative image, salt, Vandyke or whatever, to make a correction, how do you decide which number is correct?


I am referring to a scanned greyscale where it is necessary to plot the exposures of each small square. When I do it I use the eyedropper tool with a pixel size appropriate to the greyscale grid. Each square tested gives me many different readings - which one to choose?. How do you decide which number is correct or near correct?

 

[Patrick Robert James]

If you are talking about a scan in Photoshop then right click and choose your "average" area. One pixel is too small. Try 11x11 or 31x31 or whatever.

 

[nmp]

In PS, I find a better way to do is use the rectangular marqee tool to define the area you want to measure - which could be most of the area in the center of the block. Then look up the Mean RGB value (or Luminosity if you prefer) in the Histogram window which now represents the data on only the selected rectangle and not the whole image.

 

[tnp651]

The fast way is to copy the Background layer and blur the copy. Try 4-8 pixels of blur. That evens out the texture and you can use an eyedropper at the appropriate size.