Re: [Gimp-user] Gimp 2.8 pixelation on resize

[Steve Kinney <admin pilobilus net>]

On 04/19/2015 10:10 PM, Steve Kinney wrote:

> OH - in that case I missed an earlier post.  I will go back and see
> what I can make of it.  Making scaling come out "right" vs. being
> able to fix the noise would be a Good Thing.

That's bizarre.  Scaling _MG_4282.jpg to 50% or 25% of its original
size did not produce the noise, but scaling it to a width of 1920 px
did produce the pattern.  Same result with linear, cubic and sinc
interpolation.  This is what made me believe that there must be some
noise introduced by the camera's conversion algorithm, that survives
dithering to produce a Moiré pattern when the resulting image is
scaled to dimensions close to your target one.

I got the original image you posted, and enhanced the contrast with
duplicate layers set to Overlay mode, plus some color curve tweaking:

http://pilobilus.net/xfer/_MG_4282-grain-enhanced.png

I see a consistent rectilinear pattern in the nose, not obvious in
the unmodified original.  I still think this comes from some
interaction of the sensor's noise floor and whatever algorithm the
camera uses to convert sensor data into JPG format, with the same
possible remedy - save to RAW format if possible and try converting
that to a more useable format on your workstation.

:o)