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12/13/2003 01:19:30 AM · #1 |
This has been bugging me for awhile now.. many times in b&w pictures instead of having a nice smooth image I see these waves (for lack of better word) of shading, and I am not sure if this is some wackiness with my eyes, my computer or if it is due to resampling/sizing of the images.
Besides wanting to clarify this in general, I am wondering why I don't see this on winning images - even though they MUST have been resized downward to fit the challenge specifications. Is this the work (and benefit) of using PS's bicubic whatever to resize?
If so, I downloaded gimp which is supposed to have many of the same workings, but I cannot seem to find how to resize my images so that I eliminate many of those artifacts.
Others have said to simply go to scale image, but that is what I have been doing and those waves still show for me. Do I need to downsize it incrimentally each time? I tried to follow the tutorials on the site about this but they are PS-centric and I can't find how it would work with Gimp (assuming there actually are parallels between the two programs in this area).
Any help would be appreciated, though I think I may just be out of luck.
- Sia
PS: I have seen this in color photos as well but it seems the b&w is where it is most easily seen. |
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12/13/2003 01:51:56 AM · #2 |
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12/13/2003 03:09:02 AM · #3 |
The one that prompted me to ask this question right now is currently in a challenge (not my image) but the same effects can be seen in this image of mine that I uploaded yesterday - it was scaled down to 640x480 from an only slightly larger size of 1280x960 I think.. I've had this occur with the 2560s as well so I know its not size specific.
Blue Button
Can you see what I'm talking about? |
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12/13/2003 06:24:06 AM · #4 |
I think I understand what you mean. I have had a similar effect taking picture of very old B&W slides. They first look smooth but when I desaturate them or turn them into grayscale they show much more rough transitions, not as smooth.
I would guess it is due to having less "color" values to play with. When using color each pixel has an red, green and blue value from 0 to 255, so 16 M colors graduations available (256x256x256) . When using B&W the RGB each have the same value so each pixel can only have a value 256 different values, that is quite a reduction in possibilities from 16M.
Especially in a low contrast picture with soft tone transitions this will be visible. |
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12/13/2003 07:11:29 AM · #5 |
| I noticed a similar problem with my first two challenges - my picture which looked perfect in terms of clarity looked slightly pixelated when resized. I solved it by making sure that when I resized it I also made it 150 dpi and that seems to have taken care of the problem. I haven't tried this with b/w however, so perhaps this isn't what you're talking about? |
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12/13/2003 10:16:10 AM · #6 |
Make sure your monitor is set for 24 or 32 bit color.
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12/13/2003 01:40:52 PM · #7 |
Originally posted by LucidLotus:
This has been bugging me for awhile now.. many times in b&w pictures instead of having a nice smooth image I see these waves (for lack of better word) of shading ... |
If you are talking about abrupt and visible changes of color in what should be a smooth gradient, the "better word" you're looking for is banding and it occurs, as mentioned, when there are too few variations in the values of the pixels, and when there are too few pixels over which to spread the transition.
When you make the image smaller, the changes have fewer pixels over which to display the transitions, and they become more visible.
For B+W photos, shoot/scan in RGB mode, and use the Channel Mixer to convert to monochrome, or a combination of Curves to adjust the color, but never make the Mode conversion to Grayscale if you can avoid it -- leave it in RGB (or Lab) Mode. |
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12/13/2003 01:47:54 PM · #8 |
What res are you shooting your shots in? How are you resizing in PS? With the Resize option in help or thru the canvas size? Is resizing the las thing you do or do you make changes after resizing? Examples of one of your shots would be a start in getting some help.
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12/13/2003 04:17:52 PM · #9 |
GeneralE - I haven't used the Channel Mixer option before, I'm using Gimp (not PS) so I'll have to check if that's an available choice and see what I can do with it. So far I just desaturate by fiddling with each individual color in the 'Hue-Saturation' selection when doing the b&w/color thing or the 'desaturate' selection for a complete B&W - I never do the greyscale - is desaturating just as likely to create the banding issues?
Jmsetzler - thank you for that quick help tip! Changing my color bits from 16 to 32 took away all of the waves/banding I saw in the Button picture I thumbnailed, and most of the ones in other pics. That helped immensely.
I will also try increasing the resolution of my pics more to see if that helps too.
A big thank you all who answered/explained, its really appreciated and greatly helped me understand *why* it happens.
Hopefully I'll be able to help you guys with something down the road. :)
- Sia |
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12/13/2003 04:36:17 PM · #10 |
I think any technique you're comfortable with which achieves the result you want is fine. One of the great thing about computers (and digital editing) is that there's usually several "right" ways of achieving your goal.
The banding from low monitor (color) resolution is essentially the same effect as converting to grayscale -- fewer colors/shades available. You can also imitate these effects by converting your image to Indexed Color (used for GIF files). The smaller the number of colors you allow in the palette the more pronounced the effect, until you go to two colors and achieve a posterization effect (if you have a Posterize adjustment you can use that too). |
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