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I only have one image 'img', which is up-scaled by interpolation (biliner or bicubic with possible factor of 1.0x, 1.5x, 2x, 3x, etc) from the original image, which size is unknown. How can I estimate scale factor?

Here is my initial idea: do fourier trasnform of 'img', IMG = FFT2(img), check the spectrum at high frequency of IMG. The energy should reduce in high frequency because of interpolation.

The problems is: I still cannot get the scale factor.

snowgoose
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  • Did you see this post? https://stackoverflow.com/questions/7765810/is-there-a-way-to-detect-if-an-image-is-blurry Your up-scaled image will be more blurry. If you want to do FFT, I tried that: https://stackoverflow.com/questions/49674519/quantify-sharpness-using-frequencies – Gelliant Aug 06 '18 at 11:23
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    Do you know anything about the original image? – CupinaCoffee Aug 07 '18 at 12:25

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