Image of an autotype glass screen

[Schnitzel]

Hi everyone,

I'm writing an educational presentation on screening, and I'd like to include information on the analog halftoning process. For the life of me, I couldn't find a picture of the glass screen used in olden days. If someone could post a close-up image of the screen (even from a cellphone), I'd be very grateful.

Thanks again,
Shahar Klinger

 

[gordo]

Hi everyone,

I'm writing an educational presentation on screening, and I'd like to include information on the analog halftoning process. For the life of me, I couldn't find a picture of the glass screen used in olden days. If someone could post a close-up image of the screen (even from a cellphone), I'd be very grateful.

Thanks again,
Shahar Klinger

Maybe because it's a boring image?

It looked like this (quickly whipped up in PShop):

Basically black lines on glass. The lines faced away from the film negative i.e. separated by the thickness of the glass. When the exposure was being made the light would hit the lines which would cast an out of focus shadow onto the film. That out of focus shadow was effectively a threshold array.

You can replicate how it worked by following the instructions here: The Print Guide: Creating Custom Halftone Dots

Check out my blog on print-related matters (lots on screening):
The Print Guide

If you go to the "The Way Back" section you'll find some interesting historical stuff as well as quite a bit on screening..

If you want someone to cast a critical eye on your presentation don't hesitate to contact me as there is a lot of misinformation on the topic out there. I can be reached at pritchardgordon (@) gmail (dot) com

 

[Schnitzel]

Thank you very much, Gordon, for your explanation.

Check out my blog on print-related matters (lots on screening):
The Print Guide

Oh, rest assured, I've already read your entire blog, and I use it for reference every now and then. You did an excellent work there!

If you want someone to cast a critical eye on your presentation don't hesitate to contact me as there is a lot of misinformation on the topic out there.

I know, that's why I'm writing the presentation!
Thanks for the suggestion, but unfortunately the presentation contains company-specific material, so I can't distribute it outside. In any case, it is part of my job to use and develop halftone screening algorithms, and I managed to read a great deal of literature on the subject, so I'd like to think I got everything right.

Thanks again,
Shahar Klinger

 

[gordo]

Thanks for the suggestion, but unfortunately the presentation contains company-specific material, so I can't distribute it outside. In any case, it is part of my job to use and develop halftone screening algorithms, and I managed to read a great deal of literature on the subject, so I'd like to think I got everything right.

Thanks again,
Shahar Klinger

I understand.

G

 

[Alois Senefelder]

Optical Screening

Optical Screening

Gentlemen,


Some PDFs - that I hope will be of interest and value.


Halftone Reproduction, there are two theorys related to halftone reproduction using

optical screening and photo/chemical film - Dot Formation.

1) Diffraction Theory 2) Penumbral Theory



Regards, Alois

 

[gordo]

Gentlemen,

Some PDFs - that I hope will be of interest and value.

Halftone Reproduction, their are two theorys related to halftone reproduction using optical screening and photo/chemical film - Dot Formation.

1) Diffraction Theory 2) Penumbral Theory

Regards, Alois

Unfortunately the articles (typically) are quite unclear as to how the glass screens work to form halftone dots (e.g. the openings don't act like miniature pinhole cameras as stated). Fortunately it is relatively easy to simulate the glass screen halftoning process in Photoshop using the technique I described in my earlier post - i.e. The blurred, or out of focus shadow of the lines create an effective threshold array. That threshold array allows the litho film to be exposed at each opening in the grid (the halftone cell) in proportion to the intensity of light passing through it. The litho film, being binary, has a threshold response to the intensity of light that each opening in the grid allows through. That threshold response creates a dot size according to the exposure it receives.
Later, printers replaced the fragile and expensive glass screens with photographic film which replicated the fuzzy patterns (halftone cells).
Digital halftoning replicates the threshold array using algorithms that, among other things, define the threshold array and spot function (dot shape) of the specific screening design. This digital methodology for halftoning is used for all halftone screening in today's workflows, AM, FM, Hybrid or whatever.
BTW I have designed halftone screens as well as been involved in the development of commercial screens.

 

[Schnitzel]

Thank you both, guys.