Re: interpolation for a color image?

On May 25, 11:59 am, aruzinsky <aruzin...@xxxxxxxxxxxxxxxxxxxx> wrote:
On May 24, 7:59 pm, ImageAnalyst <imageanal...@xxxxxxxxxxxxxx> wrote:





On May 24, 12:14 pm, aruzinsky <aruzin...@xxxxxxxxxxxxxxxxxxxx> wrote:

On May 23, 7:40 pm, ImageAnalyst <imageanal...@xxxxxxxxxxxxxx> wrote:

On May 22, 12:03 pm, AE lover <aelove...@xxxxxxxxx> wrote:

Hi all,

I am considering the case of bilinear interpolation for a color image
(say RGB image), to apply a bilinear interpolation, will we apply the
formular of bilinear interpolation, which we use for a gray image, for
each channel R, G, and B, separately?
If so, why don't we take into account the interaction between three
channels?

Thanks

---------------------------------
I think I've seen where you get color artifacts if you do this in RGB
space, especially at edges (where the color changes abruptly).  This
is reduced if you interpolate in a different color space such as HSI
(which takes into account interactions, like you say, because the HSI
bands are weighted sums or formulas of RGB.)http://www.easyrgb.com/index.php?X=MATH

Regards,
ImageAnalyst

You cannot properly interpolate on the H channel.  Suppose you have a
red ( H = 0 degrees ) object against a blue ( H = 240 ) background..
Bilinearly interpolating to the middle you get H = 120 so you will get
a lime green border around the object. Not to mention 0 and 359 are
both red so you can get every other color interpolating within a
completely red region.

I have seen odd instances where changing the RGB gamma to 2.2 (or is
it the reciprocal) produces better results, but in most cases it is
better leave gamma alone.

Thomas Richter already said everything important.- Hide quoted text -

- Show quoted text -

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But why can't you interpolate in a more intelligent way?  You go
around the clock in the direction that is closest, so the average of 0
and 359 would be 359.5 (still a red), and the average of 0 and 240
would be 300 (rather than 120) which is a purple which seems like it
could be a reasonable and acceptable interpolation of red and blue.- Hide quoted text -

- Show quoted text -

What do you propose to do with red, H=0, versus cyan, H=180?  Either
midpoint yellow-green, H = 90 or purple, H = 270, is visually
undesireable.

RGB Bilinear 5X red vs. cyan:http://www.general-cathexis.com/images/rgbBilinear5X.png

HSI Bilinear 5X red vs. cyan:http://www.general-cathexis.com/images/hsiBilinear5X.png

HSI other way around Bilinear 5X:http://www.general-cathexis.com/images/hsi2Bilinear5X.png- Hide quoted text -

- Show quoted text -
----------------------------------------------------------------------------
I don't propose anything because there are cases where there are no
visually acceptable interpolated colors, as you proved. So there are
times when it doesn't "work" and there are times when it does.
Mathematically it can be done but it's up to the use to say what is
acceptable or unacceptable in their situation.
Regards,
ImageAnalyst
.

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