digital noise??

[imagesofarchitecture]

I use conventional medium-format equipment to record portraits in my studio. I use a black backdrop. To make

digital representations, I scan 8- x 10-inch glossy prints using a HP scanjet 8200 at a resolution of 400 pixel

per inch.

 

The problem is that the scanned images have many, many tiny white spots ("salt-pepper" appearance) in the black

regions corresponding to the black backdrop. Although a few of these spots may arise from dust, most do not

appear in the original scanned print. The effect may be digital noise caused by the scanner, but I am not sure

about that. It is extremely tedious to remove these spots. Have you seen this effect? What is the best way to

eliminate it?

 

I thank you for any help that you can provide.

Gary

[wogears]

Post an example, please.

[bruce_watson1]

Might be specular reflections from a semi-gloss print (even a gloss print, but gloss usually causes other problems like Newton's Rings). Try scanning a matte print and see if they don't go away.

[imagesofarchitecture]

Les:

 

Thanks. I will try to pose an example. The effect is difficult to see unless one uses Photoshop to enlarge the

image.

 

Gary

 

Bruce:

 

The effect is worse when I use matte-finish paper, because the scanner records the texture on the surface, which

gives by itself a "salt-pepper" appearance.

 

Gary

[obakesan]

yep ... all that is old can be new again :-)

 

sure looks like dust, noise is more regular and almost kinda "patterned"

 

I've upped the gamma to exaggerate this image to make the comparison clearer, I've marked the dust in circles and point out a patch of noise (which was buried in the darkness) in the square.

 

BTW .. make sure you post images as jpg if you want them to display inline<div></div>

[obakesan]

ohh ... some of those other white 'pixels' are probably also dust

 

ya gotta love ICE

[bruce_watson1]

Yup. That's dust. Dust comes from three major places. First, dust on the film at exposure time. Second, grunge on the film from development processing. Third, dust on the film/print at scan time.

 

Dust that's on the film at the time of exposure blocks the light and leaves clear spots on the film. If it's negative film when you reverse it to make a positive print, you get black spots in your print. If it's tranny film, you get white spots in your print.

 

Dust from processing is the same as dust during scanning -- it blocks light reaching the scanner's photo-detectors. Leaves white spots in the scan file.

 

So now you need to figure out where the dust is coming from and how to prevent it. The photographer's never ending battle with dust is legendary. It can be controlled to a high degree, but never eliminated. Sigh...

[bruce_watson1]

Also, some of the dust from scanning is due to dirty scanner glass. It can be on either side of the glass on a flatbed scanner, and either side of the drum on a drum scanner. The dust on the non-film side of either is often a major undertaking to remove and keep from returning. But sometimes you just have to do what you have to do...

[imagesofarchitecture]

Dear Colleagues,

 

I thank you for your very valuable comments. As I had feared, the major effect is dust. I do use "canned air" to blow away dust from both the print and the scanner glass. Apparently it is not effective. Perhaps the large surfaces hold too large of a charge of static electricity.

 

Does anyone know whether it is possible to access the underside of the scanner glass on the HP 8200?

 

Gary

[wogears]

Google 'hp 8200 scanner tear apart'. You are likely to come up with a manual or at least good instructions. The 'radioactive' brushes (Staticmaster, etc) are reasonably effective.

[obakesan]

Gary

 

I've heard a number of things against canned air, but mostly (to me) it seems to stir up the dust and promote static charge. I struggle on with a flat bed because I use 4x5 and even if I only used 6x9 I can't afford a LS-9000. But if you're scanning 120 roll I reckon you should look carefully at this scanner (or the 8000). The ice turns images nearly as clean as digitals. I reckon you'll find it saves you time and is faster (if not as perfect) as a drum scanner.

 

HTH

[diana_lewis]

<p>Mmmmm yes.... such great images come to mind....</p>