Monday, November 1, 2010

Oh so technical

OK, geek time. A few figures regards the resolutions and some of gear we might consider using in the hope it might serves as a handy quick reference during the process.

Resolution & Image Size: The Math

For the image to fill the entire lightbox, 2595mm x 995mm:
72ppi: 7,662 pixels high (39MP) 120MB photo - uncompressed & before crop
150ppi: 15,325 pixels high (150MP) 500MB photo - uncompressed & before crop

For a portrait image, full width of lightbox (eg. such as Marnie's test)**
72ppi: 2,938 pixels wide (11MP) 32MB photo uncompressed
150ppi: 5876 pixels wide (46MP) 131MB photo uncompressed

For a landscape image, full width of lightbox **
72ppi: 2,938 pixels wide (6.5MP) 18MB photo uncompressed
150ppi: 5876 pixels wide (25MP) 74MB photo uncompressed

** aps-c format DSLR camera or good quality scan from 35mm might be ok for these situations.

General rule of thumb: At 1:1 size, 72ppi is a good target to print from and will achieve a good result.
Up to 150ppi is better still. Anything over that though, and well that's just plain testosterone sillyness! 

Scaling image up to 72ppi for the final print file is OK (
35ppi at 1:1 would be a minimum res.) depending on the subject mater - smaller text on originals won't look so great. (Of course, if we are of Hito's school of thought, we take the good with the grain/degradation of the image and run with it!)


Full-frame Digital SLR:
eg. Cannon 5D Mark II (21MP), or Nikon D700(12.1MP)
; or alternatively, if you can get your hands on one, a Medium Format 
* Even though the pixel count is different, both of the above camera's have a comparable per-pixel sharpness.

High-Res Scan of Medium Format Transparency/Neg:
Scan of 12,000pixels ono along longest side, preferably from a 6x7 proportion trans./neg.
* Film grain is somewhat forgiving - so long as the original is in focus, noise makes up for loss of resolution and it will still look good.

The Cruse scanner at HMIF: 15,000 x 10,000 pixels (150MP)
Scan options: Scan bed (1.5x1m) or Book cradle/table (approx60x38cm?); 30min per scan. This is what it looks like. See samples here.
* delivers very flat directional light which can be 'hard' ie. the scans are meant to look flat - ie no shadows resulting in loosing and 'object' feel. Depth of field focus range is plus or minus 20mm (max). I really don't know how a hand would look in the shot. On the scan bed, objects and hands have to clear the sync-light which passes over the bed usually set at a 10cm height above (max height 15cm), ie. limbs/hands would have to be kept to the edges!
* I guess the point to used this would be to used the 1.5x1m scan bed - usually more reliable too. If the scan bed was used and scaled up to the light box height, the objects/images would appear on the lightboxes at 160% of their original size.

* One idea that's come to mind while writing this post - one scan could be split into 4 images across 4 lightboxes. It would still give us a resolution of around 100ppi at 1:1 (and objects would appear 260% of their original size when scaled up on the lightbox). Worth a thought since we have 16 images to play with.

OK so that's the facts on the table. In summary, the resolution does become significant when filling the whole lightbox area, due to the crop factor. However, there is totally room to move on these specs due to the way we might want to play out the size of the image or lack of resolution/quality.

Clear as mud?

    1 comment:

    1. thanks so much for this just scrabbling for a cam now!!