View Full Version : Evaluating a photo on the screen for focus?

3-Feb-2012, 19:02

If I'm in photoshop viewing a 4x5 bw scan and click the zoom function to view "Actual Pixels", I feel like the greatly enhanced file size of a 4x5 scan gives a different level of enlargement than i'm used to viewing Actual Pixels of dslr raw files and jpegs (much greater).

Can I use "Actual Pixels" to test sharpness/focus/scanning effectiveness on the screen?

It zooms in so much more than I'm used to it seems to zooms in more than is really that good.

At that enlargement on the screen, should the photo appear pretty sharp on the screen or definitely compromised on the screen?

I may need to work on focusing technique.

John Rodriguez
6-Feb-2012, 19:12
Altec, it depends on what resolution you scanned at and what the scanner you used can really resolve at that SPI. For example, I use an Epson 4870 and scan at 2400. With that setup if an image still looks sharp at 50% it's sharp. It won't look great at 100%.

6-Feb-2012, 20:59
Here's a little trick I use to gauge sharpness of a scan. First, I create an 8x10 image at 360 dpi from the uncorrected, unsharpened scan file. Next, I zoom into the image so that the ruler in Photoshop is equal to a 'real' ruler. I then look at the image. If it's sharp, I know I'm good to go ahead and create a full resolution master file.

I scan at 1800 spi (the native resolution of my Microtek 1800f) at 16-bit using Vuescan. At 100% (View Actual Pixels) the image on screen doesn't look too good, so I don't rely on that to gauge critical sharpness.

Really, though, the only way to truly gauge sharpness is to create a proof print and evaluate that.


Bruce Watson
7-Feb-2012, 12:10
Can I use "Actual Pixels" to test sharpness/focus/scanning effectiveness on the screen?

Can you? Of course. Should you? Probably not.

The problem is that most computer monitors have much larger pixel spacing (in the range of 72-100 ppi) than do printers (in the range of 300-360 ppi). In the worst case, you'll be looking at an additional magnification of 360/72 = 5x. That's a lot of extra magnification, so it shouldn't be any surprise at all that such an image looks soft on your screen.

If you want to know if your final print will look sharp, make a print. It's the only way to know for sure.

7-Feb-2012, 12:23
If 1.) you are viewing at actual pixels, and 2.) you intend to print at 360 ppi, then you can back up from the monitor about 3-1/2 to 4 times your normal monitor viewing distance. For me, when I've viewing a monitor closely, I'm about 14" from the display surface, and my monitor's resolution is about 100 pixels/inch. 360/100 is 3.6, and 3.6 times 14 = 51". I therefore check for sharpness at a little over four feet. The idea is to present the same pixel density to your eye as you would looking at the print. If you are printing at a higher pixel density, then back up farther (which will make it look sharper). If you are printing at a lower value, come closer (the lowest I go is 240, which I view from about three feet).

If it looks sharp from the distance that packs in the same number of pixels for a given viewing angle as what you see on a print, it will look sharp on the print. It won't be the same--the monitor is backlit and that will give it a greater impression of sharpness. But it will be close enough to estimate where you are. Experience will calibrate it further.

Remember, as you back up, you may lose the ability to see the fine detail on the screen. That's okay--the point is for the image to be sharp enough so that no matter how close you go, there is detail to the limit of what your vision can detect.

Rick "just how I do it" Denney