Tutorial: Illustrated Guide to B&W scan & processing

[Tim Lookingbill]

I don't scan B/W or large format. I'm just an ex-graphic artist/prepress technician turned amateur photographer who likes to shoot consumer 35mm color negatives with a 1995 Minolta P&S and scan them on an Epson 4870 just to practice polishing turds.

Pardon my ignorance but I can't understand why such lengthy instructions are needed for scanning a one channel/grayscale image? This isn't the only site of well meaning individuals who've written a detailed workflow on this subject. I respect the dedication behind the work put into it, though.

I just have to scratch my head and ask...Do pro photographers really have this much trouble scanning B/W? Couldn't a simple curve pull out all the detail and tonality in such a simple capture?

[David Luttmann]

You might be a photographer, but you are not a DSP engineer. This discussion sounds like a painter explaining to a weaver how to make canvas. You might THINK you know, but you don't.

Just research a bit "noise to signal ratio" and ponder on "bus width versus signal source".. Surely such pompously competent people who can "not recommend this workflow" will know all about this kind of stuff.

Note that in my tutorial I pointed that /if/ I could use JPEG2k to store compressed 16 bits sources, I would use it. I wouldn't like the throw away signal.
I think you guys are still back in the 1990s where JPEG encoders were primitives. MODERN encoders are not, I would defy you to see any artifact in a clean "source" image compressed at say, 95%+ JPEG.

/If/ you recompress a JPEG the quality plummets, but on a clean source image it's return is still fantastic. In my tutorial the image is processed AND resized before doing the "final" JPEG, that makes de "danger" or overcompressed macroblocks artifacts pretty much as low as in the original image.

Oh and the "16 bits" of your scanner is bullshit. The whole Dmax is 16 bits /for it's total exposure range/, but as soon as you move the black/white point you eat into that. A normal negative will use about 1/2 of that range, up to 2/3ish on a contrasty neg; just the base "color" will eat into that anyway. So if you get away with 12 bits precision, you are a luckly person. Note that THIS will also give you exactly the same signal/noise ratio than in 8 bits; you just get better "precision" on the noise.

Of course, if you scan in 8 bit, you throw away any extra precision you may have hoped for by using a higher bit depth. Compressing levels with a 16 bit master file is ALWAYS better than with and 8 bit one.

If this method works for you....then great. But please, don't tell me that "you defy" anyone to see the difference. I tried your workflow and compared it to a 16 bit scan and tif method and found better results from using 16 bit. Sorry, but you're wrong. All the engineering in the world cannot tell me that I can't see the difference when I can.

I will not change my workflow and reduce quality to please some arrogant DSP who obviously is well outside his realm when it comes to high quality scanning and printing.

Go blow your attitude somewhere else when you actually learn to work with what you see as opposed to what you think "should" be correct. No one here will bow down to your "DSP" expertise!

[robc]

You might be a photographer, but you are not a DSP engineer. This discussion sounds like a painter explaining to a weaver how to make canvas. You might THINK you know, but you don't.

Just research a bit "noise to signal ratio" and ponder on "bus width versus signal source".. Surely such pompously competent people who can "not recommend this workflow" will know all about this kind of stuff.

Note that in my tutorial I pointed that /if/ I could use JPEG2k to store compressed 16 bits sources, I would use it. I wouldn't like the throw away signal.
I think you guys are still back in the 1990s where JPEG encoders were primitives. MODERN encoders are not, I would defy you to see any artifact in a clean "source" image compressed at say, 95%+ JPEG.

/If/ you recompress a JPEG the quality plummets, but on a clean source image it's return is still fantastic. In my tutorial the image is processed AND resized before doing the "final" JPEG, that makes de "danger" or overcompressed macroblocks artifacts pretty much as low as in the original image.

Oh and the "16 bits" of your scanner is bullshit. The whole Dmax is 16 bits /for it's total exposure range/, but as soon as you move the black/white point you eat into that. A normal negative will use about 1/2 of that range, up to 2/3ish on a contrasty neg; just the base "color" will eat into that anyway. So if you get away with 12 bits precision, you are a luckly person. Note that THIS will also give you exactly the same signal/noise ratio than in 8 bits; you just get better "precision" on the noise.

You may be a DSP engineer but the major flaw in your whole idea is that noise is something that can be controlled with the usual digital image processing software that you are using. By which I mean, the only place where noise is a consideration is at the point of scan before the signal is converted to digital. Once digitised noise is irrelevant in analogue terms which you seem to be thinking in. The digitised values are not effected by noise. So all you have is an image which has captured noise in it. And you have no way of controlling the noise the scanner produces (except by producing negs of suitable quality)

You should read this which will show you that your theory of removing noise only achieves two things. It reduces image sharpness by averaging 4 pixels into one and introduces resizing artefacts which are not the same as noise. They are calculated digital values which are wrong.

So if you want the best quality possible from your kit you will scan at hardware resolution so as not to allow hardware or software resizing during the scan and then instead of downsizing you should print at a higher dpi which will have the the same visible effect as removing scan noise by downsampling but without introducing downsizing artefacts. This in turn means less final sharpening is required which reduces final image artefacts which are there even if you can't see them.

Anything else is just an overly complicated method of reducing filesize.

[sanking]

You may be a DSP engineer but the major flaw in your whole idea is that noise is something that can be controlled with the usual digital image processing software that you are using.

What is a DSP engineer?

Sandy King

[robc]

What is a DSP engineer?

Sandy King

Its what BUZE calls himself and which I think means Digital Signal Processing Engineer. (but I could be wrong)

[sanking]

Its what BUZE calls himself and which I think means Digital Signal Processing Engineer. (but I could be wrong)

Interesing. Is this a degree option at some universities?

Sandy King

[Christopher Perez]

No degree, as such. Think Electrical Engineering Bachelor of Science.

It means he understands, from a practical design engineering standpoint, what the effect on bus widths, signal processing, and data accuracy have on the scanning process.

Interesing. Is this a degree option at some universities?

Sandy King

[Ed Richards]

> You should read this which will show you that your theory of removing noise only achieves two things. It reduces image sharpness by averaging 4 pixels into one and introduces resizing artefacts which are not the same as noise. They are calculated digital values which are wrong.

I do not think that resizing a gif tells us anything about oversampling to control noise. Scanning at 4800 DPI and then downsampling is a reasonable way to average data to reduce noise. You start with more data points and average them. With the gif you start with the minium data for the image, then reduce it. Downsampling only works when you start with more data than you need for the final image. Since GIFs do not have any excess data, all resizing a gif tells us is that if downsampled to less resolution than is needed to define the image, that the image breaks down.

[robc]

the fact the image is a tiff is irrelevant. I've done this with a TIF and the same thing happens. I think you are wrong.

[Ed Richards]

> I've done this with a TIF and the same thing happens.

Unless the tiff has excess data points, it will degrade. Unless the tiff was generated by a random process, like scanning, it is not going to have excess data points. A scan at 4800 downsampled to 2400 or 1800 has excess data points and what is being lost is noise, not real information.