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themoleman342
Joined: 21 Oct 2007
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 Posted: Wed Jun 24, 2009 2:37 pm Post subject: "Indexed" scans |
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themoleman342 wrote:
I scanned a couple of my B&W images the other day. When I tried to edit them through GIMP I found they were in an "indexed" format as opposed to gray scale. I just converted them over and was able to edit properly. Can anyone explain what this actually did, if anything? Does it have an effect on quality?
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Orio
Joined: 24 Feb 2007
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| Posted: Wed Jun 24, 2009 3:37 pm Post subject: |
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Orio wrote:
Indexed is a very limited colour palette that is typical of gif and other low size image format, basically a prehistorical remainder of many years ago.
Your quality might not SEEM degraded but it WILL be degraded if you print and also if you perform editing on the image.
You must go into your scanner's software settings and change them to make sure that it will scan in true colour mode.
About indexed:
http://en.wikipedia.org/wiki/Indexed_color
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themoleman342
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| Posted: Wed Jun 24, 2009 3:56 pm Post subject: |
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themoleman342 wrote:
But it is only with black and white images and I save in TIFF format...does that still apply? |
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Orio
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| Posted: Wed Jun 24, 2009 4:51 pm Post subject: |
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Orio wrote:
| themoleman342 wrote: |
| But it is only with black and white images and I save in TIFF format...does that still apply? |
Yes, it will scan the images in 256 shades of gray, which is of course better than 256 colours, but it's still very low colour resolution.
It doesn't mean a thing if you save an indexed image as TIF, an image can only have as many colours as it has originally. Since the indexed image has 256 different colours, the TIF image also will be composed of 256 different colours, and the others will remain unused.
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themoleman342
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| Posted: Wed Jun 24, 2009 5:54 pm Post subject: |
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themoleman342 wrote:
The only setting that I think would apply is changing the bit depth to 16 for black and white. It is possible that the default grayscale was 256 shades. Would this rectify the problem? |
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Orio
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| Posted: Wed Jun 24, 2009 6:23 pm Post subject: |
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Orio wrote:
| themoleman342 wrote: |
| The only setting that I think would apply is changing the bit depth to 16 for black and white. It is possible that the default grayscale was 256 shades. Would this rectify the problem? |
Yes.
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my_photography
Joined: 03 Nov 2008
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| Posted: Thu Jun 25, 2009 7:58 am Post subject: |
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my_photography wrote:
256 is 8 bit color /grey shade. With 16 bit you will have 65536 color/grey shade.
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no-X
Joined: 19 Jul 2008
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Location: Budejky, Czech Republic
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| Posted: Thu Jun 25, 2009 8:44 am Post subject: |
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no-X wrote:
Truecolor (24bit total = 8 bit per channel = 16.7M colors total) palette has 256 shades of grey, becasue if you use Truecolor for B+W images, all three colors channels are aligned and because of that, 2 of them are redundant. In fact, there is no difference between Truecolor and 256 shades of grey for B+W images 
(more detailed: Truecolor has 8 bits for red, 8 bits for green and 8 bits for blue. If all of these channel store the same value, than the resulting color precision is 8 bit effective - just like 256 shades of grey)
The only difference would make 16bit (per channel) format, e.g. 16bit TIFF, or better.
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Orio
Joined: 24 Feb 2007
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| Posted: Thu Jun 25, 2009 8:51 am Post subject: |
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Orio wrote:
| no-X wrote: |
| Truecolor (24bit total = 8 bit per channel = 16.7M colors total) palette has 256 shades of grey, becasue if you use Truecolor for B+W images, all three colors channels are aligned and because of that, 2 of them are redundant. In fact, there is no difference between Truecolor and 256 shades of grey for B+W images |
I assumed he was scanning in colour mode (as he should).
This brings the subject to another point: NEVER scan in grayscale mode unless you scan things like letters or invoices, etc.
With image, one should always scan in colour mode, even if the original is B&W.
The correct path is:
- scan in colour mode (24 bit preferably)
- apply all needed edits to the image
- save an archival copy in colour mode
- convert the image to grayscale for printing B&W
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no-X
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| Posted: Thu Jun 25, 2009 9:27 am Post subject: |
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no-X wrote:
Yes, this is correct technique. I only remarked, that truecolor and 256 color palette can store exactly the same amount of data in grayscale.
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themoleman342
Joined: 21 Oct 2007
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| Posted: Thu Jun 25, 2009 3:26 pm Post subject: |
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themoleman342 wrote:
Many thanks everyone. I'm new to this whole process so these explanations are helpful. I can potentially scan in 48 bit depth. Would this be preferable? I actually don't see the opinion of 24. Only the default and 48. |
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Orio
Joined: 24 Feb 2007
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| Posted: Thu Jun 25, 2009 3:35 pm Post subject: |
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Orio wrote:
48 bit is fantastic but it can generate HUGE files.
So probably for your everyday scan you should use 16 bit unless you want your harddrive quickly filled.
And reserve 48 bit scanning for the most important photos.
24 bit would be the ideal compromise however.
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themoleman342
Joined: 21 Oct 2007
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| Posted: Fri Jun 26, 2009 11:01 pm Post subject: |
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themoleman342 wrote:
Looks like the software I have, Arcsoft PhotoStudio 6, accepts 48bit images but doesn't support many of the editing features with it. I would have to convert to 24bit to do anything. How much will I lose from my photos by this conversion?
I simply do not have the money to spend on any software that fully supports 48bit images. The PhotoStudio program just came with the Canoscan and seems to be a decent program overall. So I'll stick with it for a little while...
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Orio
Joined: 24 Feb 2007
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| Posted: Fri Jun 26, 2009 11:04 pm Post subject: |
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Orio wrote:
| themoleman342 wrote: |
| Looks like the software I have, Arcsoft PhotoStudio 6, accepts 48bit images but doesn't support many of the editing features with it. I would have to convert to 24bit to do anything. How much will I lose from my photos by this conversion? |
Purists might say "a lot", but I think that practically, this will have no visible impact on your images, except if you do A LOT of post processing and digital filtering.
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