Lee Hart and a 6800-based Kodak film printer processor

Most recent revision date of this page, Oct 14 2023. Copyright 2023 Herb Johnson, with original content copyrighted by the author.


In Oct 2023, Lee Hart contacted me about his mid-1970's work with the EXORciser and the 6800 at Kodak. In that era Kodak was the leading film photo products and services producer, including film printers. This is one of a series of accounts about use of Motorola's 6800 EXORciser systems. Lee Hart has decades of microprocessor controller experiences and currently produces a line of very small 8-bit processor kits.- Herb

Photofinishing and the 6800 microprocessor at Kodak

The project in 1976, was to upgrade a Kodak model "S" [commercial photo] printer. It was designed in the 1950's as a vacuum tube analog computer with relay logic. Its job was to look at a negative, and allow the operator to re-balance the color and density, and then make a new print of it.

It was the first microprocessor-based project we did. Kodak had a sweetheart deal with Motorola, so we *had* to use the 6800. We got the [Motorola] EXORciser fairly early. There were no [floppy] disk drives available for it at the time, so early development work was done with the teletype and paper tape. We graduated to a 6800 cross-assembler running on a Data General NOVA 1200 minicomputer.

A terminal was needed to load the program, and to load/save image data. A 110 baud teletype took *hours* to load. We went to a TI "Silent 700" model 733 terminal with dual digital cassette tape drives; it ran at 1200 baud. [The cassettes were not audio-tape but contained higher-quality digital tape for data. - Herb]

We had no idea how complex image processing would be. [The imaging array was] very low resolution; I think a 4x4 array in 3 colors. A 12-bit A/D converter measured the density in each pixel. The idea was that it measured the B/W density and color balance in each pixel, and did statistical calculations to compare this negative to "typical" negatives. Did it have the right balance of red/green/blue? Was the overall density under- or over-exposed? It would then adjust the printing of that negative to correct it toward "center".

The calculations were so slow in software that we designed a TTL hardware multiply/divide unit. It took 3 Exorcisor-size PCBs, but considerably sped up math operations. We simply copied Motorola's bus and card size, so our cards could plug into the Exorcisor to test.

The program's memory requirements grew and grew, until we wound up needing 32k bytes. Motorola couldn't supply that much memory for a reasonable price, so we wound up using Intel 2104 4Kx1 dynamic RAMs. Since we needed nonvolatile memory (to avoid spending hours loading programs and data), it was backed up with a lead-acid battery and CMOS refresh circuitry.

In hindsight, it was amazing how much we were able to do in just 32k with a 1 MHz CPU. We didn't know it was "impossible", so we did it anyway. :-)

I looked for a photo of an "S" printer, but couldn't find one. It was unique in that it was built into a Steelcase desk! The right-hand drawers were removed, and replaced with one big drawer which held all the electonics. A large box about 2' x 2'x 4' wide was bolted to the top on legs; it was a giant camera, with one roll of photographic paper on the left, and another on the right. A projection lamp was mounted in the footwell. A hole in the center of the desk let its light come up, through the negative, and up through the lenses to expose the photographic paper. The shutter assembly had red/green/blue filters, so it could control the exposure times of each color. - Lee Hart

I asked Lee Hart about the use of this digital photofinisher ...

Yes, it was a commercial product that was used by Kodak internally, and also sold to other photofinishers like Fotomat etc.

The "S" printer was used to re-print negatives that the faster fully-automated printers made a mistake on. For instance, if you dyed your skin green and dressed as a witch for Halloween, the automated printer would think the picture had been taken under fluorescent lights (which tinges everything green). So it would cut back on the green exposure time to shift your face back to a [pink] flesh tone.

But that wasn't what the customer wanted! So the negative would get re-printed on an "S" printer, with the operator keeping the green face green, but color-balancing the rest of the print. - Lee Hart

Herb Johnson
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