Extreme Gaussian Blur posterizing image?

M
Posted By
Malameel
Jan 19, 2004
Views
1964
Replies
26
Status
Closed
Hello,

I have a black and white image of a person at a podium in a room. I want to extremely blur out the background. I selected the area that I want blurred and apply the filter about 30.

The problem is that the image has a sort of posterize effect to it where each grade of grey becomes a cleanly and smoothly defined section. I tried switching to 16bit mode, but it is still there to the same degree. I am also in grayscale, and I tried RGB and that also seemed to be the same. I cannot see a difference in any of the situations.

I also tried applying the filter in steps but that doesn’t help either.

Any help is appreciated.

I am using Photoshop CS on WinXP sp1.

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L
LenHewitt
Jan 19, 2004
Have you tried using the new Lens Blur rather than gaussian?
PC
Pierre_Courtejoie
Jan 19, 2004
Or smart blur?
RK
Rob_Keijzer
Jan 19, 2004
Or your monitor on 16M7 colours?
MV
Mathias_Vejerslev
Jan 19, 2004
Adding a little noise, then blur, usually helps to eliminate some of the banding.
LH
Lawrence_Hudetz
Jan 19, 2004
Banding on smooth, subtle transitions is the bane of digital. You can find this happening in sky tone when using corner burndown or trying to help the values deepen as the sky approaches the zenith with the Gradient tool. Yes, you can apply some noise, but then you have just countered the blur!

I would love to see 16 bit output and printing capability. 65,000 steps instead of 256.

The eye is a damn good device for seeing differential values.
JS
John_Slate
Jan 19, 2004
….yeah, if he could only apply that blur in 16bit, bye-bye bandy!
M
Malameel
Jan 19, 2004
I have tried using all the blurring options available in CS, and it is still there. I have even tried combining them. Even adding noise and then blurring. This is the best option so far, by adding a small amount of blur, noise, then blur again. I can get a very blurry image, however, it gets muddy if the technique is used too much and really doesn’t solve banding.

And as said already, adding noise isn’t what I want, and removing grain and noise is important to me.

You can apply the filter in 16bit mode, but I do not know if the filter is really 16bit.

I guess it is a short coming of the current state of technology.
JS
John_Slate
Jan 19, 2004
You can apply the filter in 16bit mode, but I do not know if the filter is really 16bit.

It must not be if you still get bands! Otherwise the effect would be sufficiently dithered when going to 8bit.

I wasn’t aware that CS allowed that filter in 16bit.
J
JasonSmith
Jan 19, 2004
Does the banding show up in print?

Realize that even though the file is 16bit, your monitor is not.
M
Malameel
Jan 19, 2004
Yes, CS allows to use many new filters in 16bit not available before, but it just seems to still be 8bit results.

Maybe I need to test this out with an image from beginning to end in 16bit. I am sure that could cause problems, but I would think that a blurring effect wouldn’t matter.
BG
barry_gray
Jan 20, 2004
Applying noise and then blur defeats the original noise and you’re back to sq. one. Apply TINY amt’s of noise repeatedly.
M
Malameel
Jan 20, 2004
It seems that applying noise and then blurring the image and then repeating works vry well because the blur is not an undo. So I am not really back to square one, just a muddy versuion of square one if repeated too much.

In the end this doesn’t solve the original problem of banding, weither or not in 8 or 16bit mode.
LH
Lawrence_Hudetz
Jan 20, 2004
The answer is: If you can see it on the monitor, you will see it in the print. In fact, just because you don’t see it on the monitor does not mean you will not see it in the print.

Both are 8 bit systems.
PC
Pierre_Courtejoie
Jan 20, 2004
Could you put a link to a part of the image somewhere?

In fact, one of the best advantages of 8bit>16bit>8bit is that the second conversion can add a bit of dithering, thus lowering the banding effect
MV
Mathias_Vejerslev
Jan 20, 2004
(True if dithering is activated in advanced prefs, as per default).
PC
Pierre_Courtejoie
Jan 20, 2004
Yes, hence the "can" thanks for the addendum, Mat!
M
Malameel
Jan 21, 2004
(True if dithering is activated in advanced prefs, as per default).

I belive that Diffusion Dither (under Display & Cursors) is not set "on" as default. Should it and would it be better? I just recently did a reinstall so I know I did not change it.
MV
Mathias_Vejerslev
Jan 21, 2004
Sorry I meant Color Preferences, under the Advanced controls, dithering for conversions.
JS
John_Slate
Jan 21, 2004
In fact, one of the best advantages of 8bit>16bit>8bit is that the second conversion can add a bit of dithering, thus lowering the banding effect

Just going 8bit>16bit>8bit on a banded image will add little or no dithering. The dithering comes in when 16bit file values in the file would translate somewhere between 8bit levels, so the pixels dither to simulate the intermedate values. If you just go back and forth you basically get exactly what you started with.

Even if you do a tone change to a banded image while in 16bit, and come back to 8bit, the bands will be comprised of dithered pixels, but the well defined borders between the fields of tone will remain.

If the fine gradation is generated within 16bit, using even 12bits worth of gray levels, then dithering when going to 8bit should be complete.

I’ll be curious to see if Melameel’s Color prefs>advanced controls have dithering for conversions selected, and if not, how things come out when that option is selected…
M
Malameel
Jan 27, 2004
Sorry about being away for so long, my internet has been down at home where I have been having this issue. (I mean that I home I do different type of work and I am not hinting that my work PS is acting diifferently.)

Anyway, The banding is still there even in teh 16bit gaussian blur. However, I will check tonight if the "Use Dither (8-bit/channel images" is checked or not. Here at work it is on which I woudl assume is on by default and therefore will be on at home. However I will confirm tonight.
JS
John_Slate
Jan 27, 2004
See #18, that is the important preference, so that dithering is applied when converting to 8 bit from 16 bit.

Dithering in 16 bit is totally unnecessary, since what it does is simulate more gray levels than exist in the file. Who needs more than 65,536?

I think the setting you are checking only affects display.
CC
Chris_Cox
Jan 31, 2004
Any extreme blur will look posterized in 8 bit.

And any extreme blur wil probably look posterized in 16 bit because your display is only good for 8 bits.
J
JasonSmith
Jan 31, 2004
Which is what I was trying to say, but others disagreed with me.
H
Ho
Jan 31, 2004
Try this action (found in the Adobe Studio Exchange section):

Edgarian Blur < http://share.studio.adobe.com/axQuickSearchSubmit.asp?txt=ed garian+blur&allprods=2&submit1.x=0&submit1.y=0>

This has helped me beat posterization on *some* files. You can run it more than once if a stronger effect is needed. If you have enough history states, you can step back through the stages of the action to dial in the look you want. As always, your mileage may vary.
M
Malameel
Jan 31, 2004
As far as the dithering option "use Dither", it is checked on.

I never really solved the posterizing, and I just basically had to give up on trying solve it and get to a point where I was still happy with it.
H
Ho
Feb 3, 2004
Note to anyone who tries "Edgarian Blur": Please give it a rating using the Rate and Review section of the details page. The only rating so far is my own, which looks kind of bad because I’m the one who supplied the action. I reviewed it because it really isn’t my work, I just made it available. Dr. Edgar deserves the credit (or the criticism if you don’t care for the effect).

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