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02/06/2004 12:51:57 AM · #1 |
I've recently noticed that when applying gaussian blur (or dust & scratches or median) filters, I sometimes get strange little gradation lines, as in this shot. If you look closely, you can see little squiggley lines, kind of like a topographic map.
Is there any way of avoiding these lines when applying these filters? I have noticed that they appear most often when the filter is applied somewhat drastically. |
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02/06/2004 01:19:05 AM · #2 |
| I believe it's caused by the polarized filter. If I don't process much in PS the effect of the polarizer is good, but when you tweak with PS too much I sometimes see this same type of banding effect. |
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02/06/2004 01:30:51 AM · #3 |
I belive you are referring to the banding effect noticable in large areas with smooth gradations. This is most noticable with images edited in an 8 bit color mode as apposed to a 16 bit color modes which provides many more colors for smoother gradations. It is hard to avoid completely in 8 bit mode but it can be reduced somewhat by applying a slight amount of noise or grain via a filter in your editor. It's common with images on the internet which have to be 8 bits or less.
T
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02/06/2004 07:03:26 AM · #4 |
Is it possible to switch to 16 bit to avoid it?
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02/06/2004 07:08:29 AM · #5 |
In photoshop CS you can work in 16bit
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02/06/2004 07:20:39 AM · #6 |
| I often get this effect even in 24-bit mode... I also used a noise filter on high density but very low setting. I thought that there must be some dithering function that I just could not find, feeling stupid noising an image that I blurred to smoothen out. Is there not a better way to get rid of these lines? |
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02/06/2004 07:28:10 AM · #7 |
Originally posted by labuda:
I often get this effect even in 24-bit mode |
Everyone is talking cross-purposes here, and not really using terms correctly.
Jpeg is a 24 bit image made up of 3 * 8 bit channels.
Photoshop normally edits images in 8 bits per channel. Photoshop CS also allows you to use 16 bits per channel. |
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02/06/2004 07:50:55 AM · #8 |
24 bit? Don't cameras usualy only record in 12 bit mode 16 bit is only the space that your working in as your image is 12 bits. Thus working in 24 is pointless?
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02/06/2004 08:43:42 AM · #9 |
I had the same problem and ran my photo through Neat Image and it took those little lines away!
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02/06/2004 09:10:00 AM · #10 |
Did you perhaps increase the brightness on this shot quite a bit from the as-shot file? The bands are present to a greater degree than I am used to seeing, even working in 8-bit per channel mode.
If this is the case, working in 16-bit (per channel) mode is not going to help. The bands are a limitation of the original file. If you did not increase the brightness significantly in software, then I can't say why you are seeing such distinct bands.
Working is 16-bits per channel can help you to avoid introducing this effect, however it can't help if it's there already.
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02/06/2004 09:21:43 AM · #11 |
Some people (on photo.net) claim to take 8-bit images, convert them to 16-bit, then add a small gaussian blur (1%) to smooth out the histogram. I can't recommend it, but you might want to try it. You should do all additional editing in 16-bit too, although a wider color space is recommended when working with 16-bit.
Since you're only starting with 8-bits (per channel) of data, the advantages of converting to 16-bit are really not that great. Any editing that would cause banding/posterization in 8-bit are also likely to exist if you edit in 16-bit and convert to 8-bit. I really haven't done intensive research/testing in this area, but I would be very interested to hear about your experience.
Another option to to grab the BruceRGB working space and try working in that instead of sRGB. It's a more "efficient" suited for 8-bit editing on images intended for typical output devices. Finding BruceRGB can be tricky as it's not so commonly available anymore.
Finally, something you may have overlooked is a recent change to your color quality settings in your operating system (display preferences/settings). If they're set to 16-bit (or maybe even 24-bit), instead of 32-bit, you're more likely to see these problems. |
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