High Resolution question for enlargements

[Kphipps]

<DELETE POST>

 

[rexbobcat]

http://web.forret.com/tools/megapixel.asp

Megabytes aren't as important as image resolution.

Images that have a a lot of one tone tend to be smaller but that doesn't mean the quality is less

 

[Ysarex]

You're confused. You're looking at the photo's file size as a compressed JPEG. JPEG compression is variable relative to the image content. If your photos are 3888 x 2592 pixels and are 8 bit RGB then they are 28.8 megabytes regardless of the PPI you have set and regardless of ISO -- (3888 * 2592) * 3 = 30233088. That's 30 million, 233 thousand and 88 pixels. The 3 in that equation is there to account for RGB -- three color channels.

At 300 PPI that's a 12.9 by 8.6 print.

ISO has nothing to do with this. Higher ISO values give you noisier images but have no effect on resolution. Noise however can interfere with your recording of fine detail and this can show in a print.

If you want to print larger than 13x9 you'll have to drop the res below 300. To print 13 x 20 your res will drop to 200 PPI. As prints get larger we stand further back to view them and as a result they can be printed at lower resolution. 200 PPI should be just fine for a print that size.

Joe

 

[Pallycow]

^ what he said.

We have 24x36 and 30x40 prints on the wall for examples printed off 6 meg cameras and 12 meg cameras, at 72 dpi. Viewing distance plays a key role.

 

[AgentDrex]

Very interesting. I will have to keep this in mind as well...

 

[KmH]

^ what he said.

We have 24x36 and 30x40 prints on the wall for examples printed off 6 meg cameras and 12 meg cameras, at 72 dpi. Viewing distance plays a key role.

Whatever PPI value camera EXIF data states, can be changed post process for printing. Canon cameras for some reason typically have a 72 ppi default setting. IIRC Canon, and others, inappropriately uses the term dpi, and not the term ppi. (see below)
Print labs use the printer device RIP software (Raster Image Processor) to set an appropriate PPI for the print ordered, though many print labs will not print images that cannot be set to or above their minimum PPI values.

It is not clear if the above mentioned prints were printed at 72 PPI or that 72 dpi (or ppi) was the stated resolution in the camera.

24 inches times 72 pixels (not dots)-per-inch (PPI) = 1728 pixels
36 inches x 72 ppi = 2592 pixels
1729 pixels x 2592 pixels = 4.48 megapixels.

30" x 72 ppi = 2160 pixels
40" x 72 ppi = 2880 pixels
2160 pixels x 2880 pixels = 6.22 megapixels.

To try and keep things clear:

Unfortunately, scanner makers, some software programs, and some people who should understand the difference, use the term dpi when what they really mean is PPI. The 2 terms are not interchangeable.

The term dpi (dots-per-inch)is often used inappropriately to describe the resolution of digital photographs and other images made up of pixels.
DPI is an inappropriate term because input devices, like scanners and digital cameras don't produce dots. They produce pixels
Pixels are square (some older cameras had both square and rectangular pixels).

You might notice that Photoshop always refers to input resolution as being in pixels-per-inch or pixels-per-centimeter.

If you have a photo from a digital camera, scanned from a photograph, or displayed in Photoshop, it is always made up of pixels.

Dots are round.

DPI refers to the resolution of printing devices.

Since it takes multiple dots to print a single pixel, printer resolution has to be greater than image pixels resolution.
A typical inkjet printer can usually vary between 360 dpi (low print quality) and 2880 dpi (high print quality).

When you send a Photoshop image to an inkjet printer, it is important to understand that the number of image pixels-per-inch is not the same as the number of dots-per-inch created by the printer.