thin grid lines appear..

[ZalLazkovich]

Recently I started having the following problem.
I shoot jewelry on a white foam board. After I upload the pictures to my Mac, I crop and reduce them from 5184x3888 at 300 dpi to 1500x1125 at 72 dpi. When zooming in 100%, very thin grid lines appear covering the whole image. First I thought maybe it was my Sandisk memory card which I use for at least 5 years, so I got a newer Sandisk card. But the gridlines still show. Then I thought maybe the paper of the foam board is the reason, so I photographed a white wall, cropped and resized to the same 1500x1125 at 72, still the same problem.
What could be the problem ? Thanks!

[forum_adm]

Did you select Best Interpolation for the scaling interpolation?
Also, uncheck gamma aware scaling.

Thorsten

Screen Shot 2019-02-21 at 16.54.39.jpg (222.38 KiB) Viewed 3962 times

[ZalLazkovich]

Thank you very much!
It helped. I was using "smooth" scaling for some reason, but remember always used "best interpolation".So, using "smooth" scaling is not good.
Just curious, what it is good for ?

Thanks,
Zal

[forum_adm]

Smooth is a special algorithm. Works best if you scale by exactly 50%.

[ZalLazkovich]

Thanks Thorsten!!!