Re: Why is this (noisy k plate)?

Hector Davila

The third photo I deleted the CMYK Black channel.

samarsh@... wrote:

--- In colortheory@y..., APR <amerphoto@i...> wrote:
Why is this?

I'm just expermenting.
APR, this is where most 'breakthroughs' are made. <g>

I take an old Tin Type photo.
Can you explain? Film or print? Colour or g/scale? An old tin type
photo means nothing to me.

I then adjusted in Lab for contrast.
Have you tried an adjustment layer set to luminosity, or a regular
curve with the fade to luminosity command,or duping the layer
curving then blending in luminosity mode or etc...

I then change to CMYK and
I deleted the Black channel
(since I see a lot of scratches and spots in Black channel)
Usually nose and jpeg artifact reduction/removal is attempted in
the AB channels of LAB, or in RGB/CMYK in a duped layer set to
color blend mode. I like to combine both methods, so the
luminosity of the original is not altered, only colour.

These changes then 'migrate' into the RGB or CMYK channels,
providing cleaner noise reduction than direct removal of noise.

...and all of a sudden 90 percent of scratches and spots are
It even looks sharper than the original without sharping it.
Also, I see more detail.
I would expect this to be the case for the B or Y channels - not the
K as such...but the CMY inks can really hide artifacts in the K
channel (with a light black GCR or UCR sep). This does not
excuse a messy plate - but the K is a bit different to others.

It would REALLY depend on the image and output.

How is the CMYK conversion performed? What type of built in
setting or profile is in use? What settings, such as BPC etc.

So, why is that?
Why are the scrathces and spots gone?
Why is it more sharper and has more detail.
What is it about removing the black channel that
causes this?
Can you post the original on the web, or email it off list to me?

I then go to Greyscale mode and back to LAB and CMYK curves
to bring back the contrast and blacks.
I personally would not do this in production, but I understand that
you are playing.

I just want to know, what is the Black channel all about?
Basically, CMY do not make a nice solid rich black, but a redish
muddy dark brown. The K black plate adds definition or Key.
There are many ways to produce black, being dependent on
output and image content. The K plate is you biggest enemy and
ally when it comes to four colour print.

Hope this helps,

Stephen Marsh.

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