removing slight bands in photoshop?

02/09/2010 01:47:32 PM · #1

hi, ive got a series of photos where there is some some slight verticle banding appearing due to uneveness in light coming from my homemade diffuser, all the overall colour of the background of each shot should be a light grey but there is a slight difference in the tone of the background making some bands that are a few cms wide, its kinda like if the background is a curtain with shadows coming from the folds in the curtain, how could I easily get rid of these bands, some way to even the tones, or make them the same? thanks for any advice!

02/09/2010 01:55:18 PM · #2

It's possible that what you are seeing is being caused by the bit depth limitation of an 8 bit JPEG. Without enough potential tones, an image with subtle shading can display with noticeable bands. Does it look anything like the slight banding you can see in the sky of this pic of mine?

02/09/2010 02:00:59 PM · #3

i dont think it would be caused by that because its a area of very low contrast and the change in tone is very subtle but its so annoying, i think it is because of the homemade nature of the diffuser, its a cardboard pyrmaid like thing with several sheets of a spare white shirt placed inside at varying distances from the flash, must be so effect from the uneveness/ cheapness of the shirt material :/

Canon RF 24-70mm f/2.8 L IS

02/09/2010 02:07:18 PM · #4

One thing you can do is to make a selection of the problematic area and apply a slight gaussian blur to help even it out. The problem with gaussian blur, though, is that is will pick up smudges from adjacent colors. So, if you do this, you would first want to promote the selection to a new layer, perform the gaussian blur on the new layer, and then merge it back down into the background layer. That's something that has worked for me.

kirbic

Canon EOS R5

02/09/2010 02:16:48 PM · #5

Originally posted by brightspark567:

i dont think it would be caused by that because its a area of very low contrast and the change in tone is very subtle

That's exactly when the problem

Yo_Spiff is describing will occur. It's referred to as "posterization." When the tones change very gradually, you get large blocks that have the same color value in one or more channels. This can become visible in the final image.
The real bugger is that the less noise there is in the file, the more you'll see this effect!
I've run into this with shots that have slow graduations in the sky, in particular where I have combined several originals for one purpose or another. The solution to this is to process exclusively in a 16 bit per channel space, and convert to 8-bit *only* after all processing is done. Even then, it is certainly possible that visible posterization will occur in the final 8-bit image. I have actually added a *very* gentle dose of noise selectively to these areas to avoid the posterization. This technique works very well. Apply it as your second-last editing step, immediately before conversion to 8-bit space. Add *just* enough to dither the tones by one or two values, and add it as luminosity noise, so that you don't get false colors.
Keep in mind the "solution" that I suggest is really a band-aid on the problem... the real problem is the 8-bit limitation of JPEG. The *real* solution is to avoid JPEG altogether, but no one seems ready to move away from JPEG for web-based images.

Canon RF 24-70mm f/2.8 L IS

02/09/2010 02:24:39 PM · #6

When I ran into the 8 bit banding problem in above posted image, I found that my usual tricks to smooth out skies (such as noise reduction and selective gaussian blur) only made the problem more pronounced. It ended up that I was being my own worst critic on this one, and the banding did not seem to hurt the entry in the challenge. I think most people overlook such minor banding in a challenge as unavoidable in some circumstances. I am particularly impressed when someone posts such an entry with perfectly smooth tones.

Message edited by author 2010-02-09 14:25:02.

kirbic

Canon EOS R5

02/09/2010 02:59:46 PM · #7

Originally posted by Yo_Spiff:

See my post as to the "why" behind this... there is a solution. OK, a band-aid. It is rather counter-intuitive, but it can work pretty well.
I agree that unless it's really visible, it doesn't seem to hurt scores. I think this is because it is not noticed in the limited time that most voters give to an image.

Canon RF 24-70mm f/2.8 L IS

02/10/2010 11:23:36 AM · #8

ive had a look at the original file (raw) and the bands are still there ?! its really bugging me because the main subject of the photos are alright, but the background!!! :@ ill try some methods of blurring etc, thanks for all the help anyways

kirbic

Canon EOS R5

02/10/2010 11:36:33 AM · #9

Originally posted by brightspark567:

Blurring is going in the *wrong* direction... see my posts. Anything you do to make the file "smoother" will increase the appearance of the bands. If the bands are there in the RAW file, it's because the camera itself has insufficient bit depth. Keep in mind that even if you keep your image in a 16 bit/channel space, the camera's analog-to-digital conversion is only capable of 10, 12 or 14 bits, depending on the camera. Also, most of the bit depth is used in the brighter portions of the image; darker areas are "bit-depth-poor."

02/10/2010 11:54:56 AM · #10

ok, so ive got a load of photos now that arent too bad but have got these stupid bands that are there to stay :/, thats gonna bug me ages now...

02/10/2010 12:10:35 PM · #11

Can you post an example for us to see?

Canon EF 70-300mm f/4.5-5.6 DO IS USM

02/10/2010 01:13:17 PM · #12

eugh just tried to but i cant post links yet on the forum, hope this will work
img692.imageshack.us/img692/4764/bubbles17.jpg

cpanaioti

Canon EOS-40D

02/10/2010 01:18:11 PM · #13

Originally posted by brightspark567:

eugh just tried to but i cant post links yet on the forum, hope this will work
img692.imageshack.us/img692/4764/bubbles17.jpg

//img692.imageshack.us/img692/4764/bubbles17.jpg

(fixed your link) You need to have // in front of the string you posted and have the automatically parse urls box ticked.

02/10/2010 01:32:45 PM · #14

oh haha didnt realise that, cheers!

02/10/2010 01:43:14 PM · #15

Well, it does indeed appear to have been a reflection of your background, and not from bit depth limitations. Some selective Gaussian blur took care of it.

02/10/2010 01:51:40 PM · #16

haha, after all of that! thanks anyways for all the advice from you all, ill get to work on blurring the backgrounds, i take it you did a blur on a layer copy and used a layer mask?

02/10/2010 02:07:44 PM · #17

Originally posted by brightspark567:

i take it you did a blur on a layer copy and used a layer mask?

You could certainly do it that way. It would work for this image because the entire image is tonal variations of the same basic color. However, if there were other colors bordering the area you wanted to blur (like a building against the sky), that method could blur the other color into it in undesirable ways. The way I did it was:
-Make a selection of the area I wanted to blur, with a feather edge
-promote the selection to a layer.
-Gaussian blur the new layer
-flatten and deselect all.

By doing this, I am isolating the part I want blurred so it is not going to pick up any adjacent colors in the image.

02/10/2010 02:18:24 PM · #18

ahh right cool, i like layer masks, ie the whole non destructive process, so ill use that for these images, but thanks for your advice, im sure ill find myself using in the future