Blurring channels in LAB mode
ternoc
Registered Users Posts: 3 Beginner grinner
Hello, I am a newbie and I am discovering "the magic of LAB" in this forum.
I read an article about blurring B channel for getting rid of digital noise and I think that I could apply this technique on scans of aged slides.
I have already "trinkered" with LAB curves with good results (Photoshop CS2) but but I dont understand how to apply a blurring filter on the B channel.
Does that mean applying the B channel to the L channel ? If so what is the procedure ?
Well, could someone give a step by step kind of tutorial to overcome this problem ?
Thank you very much.
Greetings,
I read an article about blurring B channel for getting rid of digital noise and I think that I could apply this technique on scans of aged slides.
I have already "trinkered" with LAB curves with good results (Photoshop CS2) but but I dont understand how to apply a blurring filter on the B channel.
Does that mean applying the B channel to the L channel ? If so what is the procedure ?
Well, could someone give a step by step kind of tutorial to overcome this problem ?
Thank you very much.
Greetings,
0
Comments
To apply a filter to a channel you need to target that channel in the Channels Palette. By default the Channels Palette shares space with the Layers Palette. If you don't see the Channels Palette you can always get to it through the Window menu.
Once you have the Channels Palette in view, click on the channel you want to target:
Now when you run your filter, it will only affect channel b. When you are done click on the 'Lab' channel to go back to targeting all the channels.
Also note there is a short cut to target a particular channel. Notice in my screen shot that I can target channel b by pressing Ctrl + 3 (on a Mac it would be Command + 3).
And even though you can blur the a and b channels much more heavily than any of the RGB or CMYK channels and get away with it, since all the detail is in the L channel, you still can get some color drift at the edges between objects. Surface blur is a useful option since it preserves edges much more than standard Gaussian blur.
—Korzybski
I'm well aware that I have to target B channel in Channel Palette. I's what I do applying a blur filter on that particular B channel. But it makes no visible difference (even with the strongest blurring) once you have cliked on the "eye" of the LAB channel to see the picture "full colors". It's why I have asked the question.
Nevetheless, there is some difference. You can notice a striking difference on the blue channels (after reconverting the image to RGB) between the Background and the Background copy.
Why this difference is not visible in the Layer Palette between the 2 layers "full colors" (Background and the Background copy) ? Despite a very slight change of colors these 2 layers seems identical !!
Am I missing something or does it work only with pictures with a terrible digital noise ? (I can't find one at the present time to test it)
Greetings
Digital noise is typically seen in the Blue channel when the image is significantly underexposed, which should not be present in a well scanned slide as the scanner/technician controls the exposure.
Is the noise that you see in the A and B channel, or in the L.
I suspect you may be seeing grain from the slides themselves, in which case blurring the B won't make much difference. Good slide scanners easily pick up the grain from the emulsion on higher speed slide films, or color negatives or B&W negatives.
This image was shot in 1945, on Kodachrome, and definitely has grain compared to modern digital images. It was shot with a manual focus, manual exposure 35mm camera by my father as a serviceman at Fort Sam Houston.
Post your image - let us see it.
Moderator of the Technique Forum and Finishing School on Dgrin
Once you suggested to me that because there was a bit of noise or something bothering you that perhaps it would help if I sharpened it by converting it to LAB, doing the channels separately, with GBlur on the A&B channels set at about 6, and do the sharpening on the L channel.
Since then I have just incorporated it into my work flow with no real understand of what I am doing. If I am pretty sure the noise is low or non existent, I lower the blur numbers.
But doing it that way seems to bring out a more saturated look in the finished sharpened product. I just deal with it if it is too saturated, often it does not seem to be. I have wondered why this happens, though.
Do you usually incorporate this method into your workflow, PF, or am I doing "work" that I don't need to be doing?
I feel guilty when I don't do it. I have to be in real hurry.
ginger
No, I do not do a GB on th A or B channel, except in very unusual circumstances.
If I have image noise from a high ISO, I will use Neat Image or some plug in to reduce the noise.
Generally, I try to avoid having noise in the first place if that is possible.:): Do not feel guilty about not doing it. There are easier ways ti increase saturation of colors - either in RAW conversion, or Overlay blending or increasing the curves in the A and B channels.
Moderator of the Technique Forum and Finishing School on Dgrin