Need Help with Utterly Simple Problem (aka unsure of basic photography knowledge)

lennon33x · Jan 13, 2014

KmH said:
What type of resolution are you asking about? There are 2 kinds of resolution. 1. The resolution needed for electronic display, which is just the pixel dimensions of a digital photo. My 24" computer display is set to show 1600 px by 1200 px. But, I can change that display resolution if I want to. 1600 x 1200 fills both the shape (width and the height, or aspect ratio) of my display. If a photo is 3872 x 1683 pixels I can't see the entire image at 1 pixel to 1 pixel on my display because the image is bigger than my display is set to show. For that reason, most web pages automatically reduces the zoom factor for a photo so the photo will fit in the space the web page code allows for photos. 2. The other resolution is print resolution. Print resolution is the pixel dimensions AND the pixels per inch (ppi) value. PPI has no meaning for electronic display. To simplify matters lets use even numbers - a photo that is 3000 pixels by 2000 pixels. A 3000 x 2000 photo set to 100 ppi will be a print that is 30 inches by 20 inches. Here is the math 3000 px / 100 ppi = 30 inches (pixel units are on both sides of the equations - and cancel, leaving just inches from the denominator) 200 px / 100 ppi = 20 inches. The same 3000 x 2000 pixel photo set to 300 ppi will be a print that is 10 inches by 6.67 inches. So to get a bigger print we didn't have to change the pixel dimensions at all. Plus, a larger 30 x 20 print will be viewed from a greater distance than a 10 x 6.67 print so the fewer pixel per inch the bigger print has likely won't even be noticeable. Back to increasing just the pixel resolution of a photo. To do so pixels have to be invented that didn't existed in the original photograph. There are software applications that look at the original pixels and then guess what new pixels need to be created to increase the pixel resolution of the photo. Some of those applications do a pretty good job.

I tried to make the two interchangeable in my head. I was thinking how a digital resolution of a photo that had such high pixel requirements would be equal to those that are printed. I guess we are talking about two different animals.

orljustin · Jan 16, 2014

MicheleT said:
Mugs Please select a maximum quality JPG (RGB Color) that is exactly 4600px (width) X 2000px (height).

Laptop & iPad Skins / iPad & iPad mini Cases Please select a maximum quality JPG (RGB Color) that is exactly 4600px (width) X 3000px (height).

I shoot at the largest file size. I am using a Nikon D60 which is my backup camera. I also have a Nikon D5100 which is having major shutter issues right now. So, (and here comes the ignorance) if my file is 3872 x 2592 pixels

This is being made into a big deal, when it isn't.

1. In Photoshop, or other program open Image->Image Size
2. Type in 4600 for width - hit OK
3. Choose crop tool
4. In options boxes type in 4600px and 2000px
5. Use tool to crop to maximum width, and then crop vertically to select best area up and down
6. Save and upload.

KmH · Jan 16, 2014

You gave them a fish they can eat today.

Why not teach them how to fish so they can eat fish every day they fish?

apaflo · Jan 16, 2014

KmH said:
What type of resolution are you asking about?
There are 2 kinds of resolution.

The two you discuss... are just exactly the same thing!

1. The resolution needed for electronic display, which is just the pixel dimensions of a digital photo.

The electronic display only has so many pixels. Resolution of a display is measured in Pixels Per Inch, though historically is called Dots Per Inch. Typically today most LCD displays are close to 100 PPI. It might be a little more or less. For example I use a pair of NEC monitors that are 1600x1200 pixels and my video driver says they are 99 DPI. At 99 DPI that means the 1600 pixels across a horizontal line covers 1600/99 inches, or 16.16 inches. Those values are cast in concrete and cannot be changed.

Hence a 4000x2000 image, to be displayed on my monitor, must be reduced in size by at least from 4000 to 1600 pixels before it is displayed.

2. The other resolution is print resolution. Print resolution is the pixel dimensions AND the pixels per inch (ppi) value. PPI has no meaning for electronic display.

That is exactly the same type of resolution as discussed with a monitor. The only difference is that printers have a higher Pixel Per Inch
parameter.

For example, HP and Canon printers usually print at either 300 or 600 PPI, while Epson printers use 360 or 720 PPI. That is as compared to the 100 PPI of my monitor, but it is exactly the same thing. It is also "cast in concrete". We cannot decide to use some artibrary PPI value for either display on a monitor or a print, and when we talk about it as if that were true (saying we can get good prints at only 200 PPI but the best is 300 PPI) what we mean are "original pixels" in the image before it is resampled for display or printing.

And that leads to gross amounts of confusion!

To simplify matters lets use even numbers - a photo that is 3000 pixels by 2000 pixels.
A 3000 x 2000 photo set to 100 ppi will be a print that is 30 inches by 20 inches.

If fact there are no printers that will print at 100 PPI, and setting the image to that will do nothing because all printers will totally ignore it.

For example, I use Epson printers that mechanically print at 360 PPI. If I feed the printer a 3000x2000 pixel image it prints a 3000/360 by 2000/360 inch print (8.3"x5.6"). If I want a 30x20in print it necessarily must be resampled to produce an image that is 360*30 x 360*20 (10800x7200) even though we typically say it is being printed at 100 PPI. What we mean is the original image had 100 pixels to make each inch of the eventual print; but in fact the printer necessarily had to see exactly 360 pixels per inch to make a print.

So to get a bigger print we didn't have to change the pixel dimensions at all.

You do change the pixel dimensions, and just as with the monitor display, the driver will do it automatically if needed.

You can give a print driver a specific image with whatever the pixel dimensions are and either let it print at the size appropriate to that pixel dimension with it's PPI, or you can tell the print driver what physical size the print should be and it will resample the input image and send the appropriately resized image to the physical printer. Either way the PPI of the printer doesn't change.

Back to increasing just the pixel resolution of a photo.
To do so pixels have to be invented that didn't existed in the original photograph.
There are software applications that look at the original pixels and then guess what new pixels need to be created to increase the pixel resolution of the photo.
Some of those applications do a pretty good job.

That's very true. Resampling to either upsize or downsize is a very complex subject if one wants to be very critical.