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Old 09-27-2007, 08:09 AM   #1
john_b
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Default greyscale images: TIFF v JPG

I thought I was reasonably familiar with features of the main image file formats. I wondered, though, about storing greyscale images since I'm intending to scan in some old family (b/w) negatives.

I think I'm right in supposing that if I scan in 16-bit greyscale mode then TIFF is quite suited for that. But is it necessarily the case that JPG - even though it has 3 x 8-bit channels available - can only ever store greyscale images in a maximum of 256 shades of grey?

File sizes are not an issue in this case, but on the face of it JPG is just not suited for greyscale - or have I missed something?

Grateful for any advice.
John
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Old 09-27-2007, 08:27 AM   #2
LoisWakeman
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I believe that greyscale JPGs are always 256 shades (8 bit), yes. PNG also supports 16-bit grey, as does TIFF.

However, in practice rather than theory, JPEG seems to work well for monochrome use as long as you don't over-compress it.
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Old 09-27-2007, 08:57 AM   #3
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Thanks, Lois. It just struck me as a bit odd that storing a greyscale image in JPG format means that the three channels are - presumably - holding the same information.

I agree that I'm probably not going to be able to tell the difference between an 8-bit greyscale image and a 16-bit one. Perhaps there are those who can, but, in any event, if I can scan in 16 bit mode (and save it as a TIFF) then I might as well do so.

I still use an old copy of PSP (v4) for some purposes because it opens quickly and is particularly suited to the job. I have noted, though, that it refuses to open some TIFF images although it's happy with others. I just had a feeling that flavours of TIFF were perhaps not quite as universally supported as JPG and, of course, future-proofing your images is quite crucial... but that's another issue...

Thanks again.
John
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Old 09-27-2007, 10:44 AM   #4
don Arnoldy
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Originally Posted by john_b View Post
File sizes are not an issue in this case, but on the face of it JPG is just not suited for greyscale - or have I missed something?
JPG's main advantage is the potential speed of compression/decompression. It is lossy--every time you resave a JPG, you lose a little more information from the file. I would not save the original scan data as a JPG--use TIF.

   
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Old 09-27-2007, 11:07 AM   #5
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I would not save the original scan data as a JPG--use TIF.
I think you're right. The scanner does give me an option to scan in 42-bit colour but presumably JPG can't handle that? I don't know whether TIFF can but in any event, it does seem a bit over the top...

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Old 09-27-2007, 11:36 AM   #6
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john_b: I wondered, though, about storing greyscale images since I'm intending to scan in some old family (b/w) negatives.
I've scanned old family images in RGB because there are gradations you will miss if you scan greyscale and you may find greater flexibility when processing the scans--experiment and see.

All of the images on my Remembrance and Remembrance 2 webpages were scanned RGB and many were later "greyscaled" by using Photoshop's Channel Mixer which allowed me to pick and choose which RGB channels (and how much) individually to get the best b/w image I could.

The only time I save any of these images as jpg's is when I am creating images of them for a webpage--basically, I don't consider jpg a "good" format for archival purposes...

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Old 09-27-2007, 12:00 PM   #7
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I've scanned old family images in RGB because there are gradations you will miss if you scan greyscale and you may find greater flexibility when processing the scans--experiment and see.
Oh dear, this is leading me into unfamiliar territory...;-)

In effect, you're saying that scanning a b/w image in colour will give you greater control over the final image, right?

I looked at the pages you mentioned and wondered whether you were referring exclusively to scanning prints - which they mostly seemed to be - or whether that also applied to scanning b/w negatives as well?

I must say that this hadn't occurred to me at all although I see the point you make about using the three channels.

So the choices seem to be boiling down to scanning in 16-bit greyscale or 3 x 8-bit RGB - is that a fair summary?

Eek - now I'm scared!
John
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Old 09-27-2007, 02:12 PM   #8
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Default Scanning Old Photos

A year ago I scanned a number of old photos, including some color photos and some black and white photos, but I never thought of scanning in anything other than color, and with a fairly high resolution, at that, with the result in TIFF format. I then worked with the scanned photos using Paint Shop Pro 6, to erase some of the problems with the originals with cloning and other techniques. I then printed the results on a color printer for framing.

Are you intending to print the results, or are you intending to put them on a website? Really big files are of little consequence on a home color printer, but they should not be placed on a website. High DPI scans can be edited and printed well, but are not of value for emails or web sites, where some thought as to load times, even with broadband, should be given. I am not an expert by any means on scanning or digital photo editing, but that is my personal experience.
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Old 09-27-2007, 02:56 PM   #9
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john: or whether that also applied to scanning b/w negatives as well?
I'm sooo sorry!!! I completely missed that you were talking about negatives...duh...

I've not scanned b/w negs but I think I'd at least try scanning one in RGB if that's possible and compare it to the same neg scanned greyscale.

What scanner are you going to use? What scanning software?

I have a Minolta Elite II slide/neg scanner and an Epson 2450 flatbaed although I've never used the flatbed to scan slides/negs. I use VueScan with the Minolta and it's excellent scanning software...


>>In effect, you're saying that scanning a b/w image in colour will give you greater control over the final image, right?

Yes...although with negs, I'm not sure that applies...


>>So the choices seem to be boiling down to scanning in 16-bit greyscale or 3 x 8-bit RGB - is that a fair summary?

Yeah...


>>Eek - now I'm scared!

LOL!! Don't be...keep us posted...I'm most interested...

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Old 09-28-2007, 01:33 AM   #10
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A year ago I scanned a number of old photos, including some color photos and some black and white photos, but I never thought of scanning in anything other than color, and with a fairly high resolution, at that, with the result in TIFF format.
Are you referring to scanning prints, though, rather than negatives? I don't know if b/w prints should be treated in a different way to negatives?

In any event, I think TIFF is the way to go with these but I did just have a few concerns in that there seem to be different flavours of TIFF... perhaps it's the old story where it's decided to 'improve' something that already works perfectly well...;-(

John
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