How much is enough?????

[ignatiusjk]

What should a good pixel count be for a 16x20 from a 4x5 neg? I was always told that 7500 for the width was enough.Whats more important to scan to pixel count or to target size? Will either give you a better scan.

[Peter Mounier]

If you print at 300 ppi, then you will need 4800 pixels for the 16" dimension, and 6000 pixels for the width.

So if you scan the neg at 1200 pixels per inch, the 4" side of the film will get the needed 4800 pixels for printing at 300 ppi.

Whether you choose target size or pixel count, the scan will be the same. Choosing target size just arranges the pixels per inch for you when saving the file.

Scan at a higher resolution if you intend to crop before printing.

Peter

[Peter Mounier]

Now that I think more about it, the neg isn't exactly 4x5. More like 3.62"x4.62". So to fill the 4800 pixel requirement for 16", you will need 1326 pixels per inch (1326 x 3.62" = 4800.12)
Scan higher res if you intend to crop.
Sorry about the confusion.

Peter

[memorris]

I use SilverFast and there is a difference between the size and DPI settings. If you use the size so the scale is > 100% it scans at the specified DPI and then in s/w enlarges the image. If you set the DPI appropriately you get the maximum resolution. I once argued that the were the same with a friend and he proved it by showing me 2 scans of the same negative at 100%.

To scan for a specific size, take the desired dimension and multiply it by 300 unless you are using an Epson printer then 360. Then divide this by the scan size. This will give you the DPI to use. If the w:H ration is the same on the scan as the output, either dimension will work. If not, use the one that will need to be the largest.

[tlitody]

What should a good pixel count be for a 16x20 from a 4x5 neg? I was always told that 7500 for the width was enough.Whats more important to scan to pixel count or to target size? Will either give you a better scan.

work backwards from your output device. So if you have epson printer and are printing at 360ppi, then a 20inch image needs 20x360 = 7200 pixels. Then if your scan area is 4.62 inches wide, you need to scan at 7200/4.62 = 1558 spi at 100%.

[mrladewig]

Or just scan at the optimal res for your scanner and reduce the pixels with bicubic sampler in photoshop to the size you wish to print. This way, you only have to scan once, only have to remove dust once and can have a master file for whatever print size you wish to use.

But in the end, if printing on an Epson the ideal native resolution ppi is 360 or 5760*7200

Many other printers run at 300ppi native resolution so in that case a 4800*6000 image is ideal

Some printers run at 400 or 600ppi.

[maximogaia]

Thank you for the info. Very helpful