I've been having some serious dithering problems on my photos lately, especially when I want to add a heavy vignetting effect. A pretty good example of the problem shows in the top left corner of .

Do you know a way to get rid of this? I'm postprocessing in 16 bits and saving at the highest possible jpg compression, but it still shows up...

I have the same problem.. Many good photos is destroyed by this.. It really #¤%#"" me off!
I guess the main problem is your graphic card. Then your screen.. maybee the moust important is that you cant push your digital photos to far in levels, contrast and saturation. It mainly shows in non detail areas, like the sky and things like that. (By you, i dont mean you in particular, to make that clear! :O)

If anyone knows how to minimize this problem, i will get happy too..
/
Elisabeth

Hi Alexandre.

I come up against this problem quite a bit at work, the best advice I can give is to first don't use multiple adjustment layers on these areas. Try to get your results with just one adjustment. Sometime a add noise level as low as .5 will help. Secondly if you still have problems, noise is you answer. If you are careful you can add some noise, which will remove the banding but not enough that the noise will be visible. A great way to add noise is to create a new layer, fill with 50% gray then change its blending mode to overlay, and then finally add noise to this layer. This method does work, but sometimes is quite tricky. The best way is to avoid multiple adjustments.

Alexandre i had a look at it, does it look like this before resizing?
You can also do a vignette by overlaying the original photo with a copy of it and then underexpose the copy (with photoshop) and then use a soft eraser to erase the middle part of the photo. dont know if the result will look better.

I would like to know how do you add vignette, then I could give you some advice on that workflow. :-)

At the moment, I add vignette by using the lens distorsion filter, as I rarely manage to get good results when creating manually the mask. This happens even when said vignetting is the only modification applied to the area.
I can't check right now if this is the same at 100% in this specific case, but on other photos, the gradient looked fine when observed at 100%, it was only when resized (either "for real" or just unzooming) that the ugly dithering appeared.

Oh ok, i had the same too. when printing out large its ok or when zooming in. maybe the grafic card or monitor?

that's the point :-) adding with the filter it creates those "newton rings"
the gradient is too fine, and when you resize then you get that banding and dithering.
check out my "spice up" article, there is a step to create a vignette :-)) try it out.

cheers :)

I think the answer to the original question is not to save as a Jpeg at all. If you have shot in Jpeg Open the file and save as 16bit Tiff or Psd. You can then work on the Tiff file without these dithering problems. What's happening is when you save as a Jpeg it 'dumps' any pixels that are not being used when you 'remap' (Levels or Curves). As you say it shows most in sky's and any graduated tones, but it is happening all over your picture.

I'm afraid it's another reason to shoot Raw.

If you have CS3 and Raw Converter V4.1 or higher you can right click on a Jpeg (or Tiff for that matter) and open it in the Raw converter, doing any manipulation here is lossless as the changes are written to a 'sidecar' (xmp) file that acts like an adjustment layer and the image is viewed through it, it doesn't touch the original file at all. Then open as a 16bit file.

Other than shooting occasionally in Jpeg, Jpeg does not come into my workflow at all, Psd or Tiff are much better options.

Dithering caused by graphics cards is largely a thing of the past as even the cheaper ones have 128Mb of memory which will allow large resolutions without dithering, but if your screen is set to 3000 X 2000 that could be the problem, but then other people wouldn't see it on their screens.

Chris

I always shoot in raw and edit 16 bits tiff files, but have to save as a jpg at the very end of my workflow, for display on the web. This is the only moment jpg are involved in the whole process.

I see what your saying Alexandre, what I said doesn't count. - sorry. Does the problem occur before or after you save as a Jpeg, is it a problem when you print?

Chris

No worries :-)

It happens before I save as jpg, sadly. And I don't (yet) print, so I can't know if it's a problem there too. But I'll use Vernon's method for adding vignetting next time, and keep my fingers crossed...

have it happening sometimes as well, both in Picasa and PS regrettably. and it is always most visible in (rather large) smooth areas with a very delicate graduation in tones. Drives me crazy, as I don't know a way around it :(
Happens to me as well before resizing and saving as jpeg. I do shoot in jpeg though.
As I mostly convert my photos to b&w, it is during the conversion that it happens. Think it doesn't happen if I just desaturate the photos, but that doesn't exactly give me pleasing results.
Had a small conversation with King about it, as even he had it happening with some of his last uploads. Seems to me that the best way around it is to just get things as right as possible in camera, so that you don't need to fiddle with contrast and tonality too much anymore in post processing. Regrettably, getting things right in camera is not my strong point :(

Have heard of this before, it has been suggested in another forum that your raw convertor can make a big difference and especially whether there is any noise removal at this stage. I would suggest doing no noise reduction until the very end of processing and maybe try a different raw convertor. Canon DPP is prettygood for not getting this effect and also Capture One. Hope this helps.

Found the original thread in other forum here, lot of testing done on various raw convertors, worth a look.

No link....

Sorry...

No link...

maybe here
http://www.onexposure.net/forum.php?action=viewtopic&tid=744&jpg-or-raw

Sorry, here is the link I meant http://www.potd.com.au/forum/viewtopic.php?t=1918&postdays=0&postorder=asc&start=0

that was an interesting article david. thank you.

1. edit the picture in 16bit, not 8bit
2. try adding a new layer with some monochromatic noise, just enough so the dithering disappears. worked for me :)

Martin

A vignetting technique that works for me is this:

create new adjustment layer - levels
run shadow and midtone sliders to the right to darken image, until you get a smooth corner darkness to your liking
Stay on the current adjustment mask and hit the gradient tool - choose the radial type
Run a line from the center of image to any corner and you'll have a nice smooth gradient

Optionally, change later blending to multiply and reduce opacity a bit until you're satisfied.
If the central focus of your shot isn't in the center of your image, you can paint out or in parts of the gradient on the layer mask until you get something that works

Many of my images have long tonal gradations. I work with large image sizes and sometimes get banding after reducing the image size and resaving.

As Martin says, adding a bit of noise can help. I tried creating a nice tonal graduation in Adobe Illustrator, then brought it over as a layer, that seemed to help. I keep it handy. Now when saving a smaller file as a jpeg, I add the subtle graduation of tones, the layer that is causing the problem, only after resizing the image and just before I save it.

However, all these steps are part of the struggle. I still don't feel any sense of mastery over this problem.

IMO, the most important thing said above is 16bit. Makes much bigger files and more processing time, but well worth it, especially if you are doing a more involved treatment that you would not want to have to re-create. I either convert from raw into 16bit psd or scan from film at 16bit.

Here's my headache:



This was rejected because of the banding (dithering) visible mostly in the lower left area. I went back to the original file and tried to remove banding by adding noise:



This was also rejected as the screeners preferred the original composition (I can't see a difference but then I'm not a screener...). So, I tried desperately to remove banding from the file I uploaded first, trying to correct it by adding selective noise. This was the only method I could try - there's allegedly a way to correct banding by playing with the red channel in channel mixer but in a BW convert it doesn't make much sense.



This was the final attempt which was rejected again. It would be cheap to argue that photos with bigger flaws have been published but let's not touch this subject. I consider this a challenge.

After thinking a lot about a method to solve this banding problem and much of fruitless googling, I can only think of one solution: uploading larger files where we don't have to apply as drastic resizing as we do now. The 750 pixel limit for portrait format is just not big enough (even if the system occasionally tolerates 800 pixels). This will be obviously not be on top of Jacob's to-do-list, so until then all we can do is to reheat this topic... maybe someone has discovered the philosophers' stone since the last post? :)

Yes, it's a haedache but most annoying happens while doing some skin softening, do you have any advice? It doesn't happen always but sometimes even a single layer causes this dithering and can't be solved via vignetting.

A very bothering issue indeed... at least I am happy to figure out that my crappy PP skills can't be accused for this... :))
If it seems we have to deal with that I wonder what is the less worse : ugly banding or diphering noise ? what do you think ?

PS: composition is indeed different: #1 and #3 are cropped version of #2 with more compact aspect ratio. #2 shows more space on right (see at the level of knee).

Yep. Indeed. I forgot to take my eye drops. Anyway, I call on my fundamental human right to say something stupid once in a while.

The more I think about this - and the more forums and how-to's I read on the net - the more I believe it has nothing to do with our PS skills. Banding/dithering is technically determined by our 16-bit browsers' capability to render details of small to medium sized images. I found an interesting thread about this:
http://www.photoshopgurus.com/forum/quick-tips-techniques/121-succesfully-removing-banding.html
... where they discuss a method that could or could not work in color, but unfortunately not really useful for editing BW photographs.

??? 16 bit browser? Computer language?
16 bits adds up to 48bits in rgb, 16 bits per channel.
This is where some of the problem might be. I have the same problem with many underwater shots in the darker area. To avoid it I work all the way in 16 bit(per channel), then change to 8 bit mode when I need to make a jpg.
The darker areas have less resolution on the sensor, and when the resolution is "dumped" even more by converting to 8 bit it is hard to make any contrast adjustment any more without banding.

Sorry, have not had time to read all posts, so I might just have given the same info as some others

If that's a headache, I want a migrane.

I think the only way to truly remove the banding using the least grain possible is to add 1.3-2.5 grain in photoshop.

I don't know if this article helps eliminating the banding in your images, but I think it shows when you will run into problems.

@Balazs, I don't think the problem has anything to do with size. This is a problem we have fought for years in the TV and Film graphics industry. The banding is caused when the change in value between on line and the next is smaller than one "bit". What the software does is to round off the value so that you get repeated values and then all at once the value jumps to the next higher available value in your color/bit depth. I was not aware of any internet viewing capable of 16bit. I think all browsers are 8 bit and certainly jpeg only supports 8 bit. The ONLY solution I have ever seen to an image that has this kind of very subtle graduation is to capture and process in deeper bit depth than 8. When I shoot with my D90 I always shoot in Raw + Jpeg. Sometimes I just use the jpeg, but mostly I convert the raw file to a 16bit Photoshop file and do all my processing in 16 bit, including printing. I ONLY convert to 8 bit for jpeg for the web and only at the very last step right before I re-size. And when I scan film using my Nikon 4000, I scan in 14 bit and save as Raw. Then from there the process is the same as with the D90 files.

The reason 16 bit processing does so much to avoid banding is that there are WAY more values for the software to choose to assign to each each pixel or line of pixels in a subtle graduated area of an image. You tend to get WAY fewer repeated values and, therefore, almost no hard transitions. 8 bit files have only 256 choices for value for each pixel. 16 bit files have 65,536 choices for value for each pixel.

The idea that noise or grain can "remove" banding is a technically a myth. All the grain does is to disguise the banding. Now, sometimes I will admit, it does a very nice job of disguising the banding, but it technically does not remove it. What happens is that the grain tends to diffuse the hard transitions between one value and another, so the repeated values are much less noticeable when they transition to the next 8 bit value.

Absolutely yes. Thanks for elaborating this.

Exactly!

I may be wrong, but it is the lack of 'dither' that causes these banding proplems. The problem referred to occurs in areas of gradual, smooth gradation of hue or luminance. Jpegs are made up of MCU (minimum coded units) blocks and the 'macroblocking' over areas of smooth brightness gradation gives rise to this banding artifacts.
Dither is an intentionally introduced noise in order to prevent theses quantization errors.
I recall in the days of 4 bit colour, that dither was the introduction of adjoining colours in order to great the illusion of additional colour shades. Thus red, white,red produced a dithered pale red.

Yes, dither is the interpolation of neighbouring pixel values to achieve smooth tone transitions, but it is not noise because noise is random.

Use of any editing tool which works by resampling and redistributing pixel values such as levels and curves will cause posterisation/banding.

If you have this problem already in an image I have found that the Descreening tool in onOne's PhotoTools can help.

Very interesting and helpful thread!

I also urge you all to read Dave Nitsche's comment in this thread

http://1x.com/v2/#discussions/17288/cropping/

brose