Question about resolution of still pix on Canon PowerShot SD30?

Question

I took a photo with the Canon PowerShot SD30 (after not using it for a while, so I didn't remember much about it) and was surprised that the resolution was only 250 dpi. I was asked for a higher resolution (this would be for Internet display primarily). The manual confused me since it did not express resolution in a dpi number like 300 or 400. (I am used to such numbers used in scanning, whereas for digital cameras it seems to be different.) What's the relationship, if any, between the resolution as expressed in dpi and the image size?

The advanced manual, under "Resolution" settings, gives these choices for still images:

Large= 2592x1944 pixels
Medium 1 = 2048 x 1536
Medium 2 = 1600 x 1200
Small = 640 x 480

I had the camera set for a high-quality compression setting (Superfine--don't know if that has anything to do with it).

The advanced manual, under "Resolution" settings, gives these choices for still images:

Large= 2592x1944 pixels
Medium 1 = 2048 x 1536
Medium 2 = 1600 x 1200
Small = 640 x 480

I had the camera set for a high-quality compression setting (Superfine--don't know if that has anything to do with it).

Eric Lefebvre · Accepted Answer

DPI is only important when printing and can be set at the time of printing. It stand for Dots Per Inch.

The actual resolution in terms of pixels is what is TRULY important.

Let's take your large setting.
2592 X 1944 printed at 250DPI would result in a print of 10.36 inches by 7.77 inches.

A small file (640*480) printed at 250 DPI would give us a print of 2.56 inches by 1.92 inches.

Now let's say you are printing your large file (2592 X 1944) at 300DPI. The print would be 8.64 inches by 6.48 inches.

At 400DPI? 6.48 by 4.86 inches.

400DPI is ridiculous ... 300DPI is used for what's calledd offset printing ... it's what you use for printing brochures and the likes where the quality needs to be really high from really up close but if you are printing a large art print meant to be looked at from a few feet then you can drop the DPI down significantly with little to no PERCEIVABLE loss of quality.

Think about it like this ... billboards look pretty shrp and crisp to you when you look at them from the side of the road right? Well they are printed at something like 5 DPI. Each inch of the print only has 5 dots.

So printing your large file to a billboard at 5DPI, we would have a print about 518 inches by 388 inches or 43 feet by 32 feet.

ps.: 5DPI is just a random number ... it's probably more like 10 or 12 DPI, I don;t do billboard prints. :)

Heck 400DPI is pointless even due to paper absorption ... the paper can't absorb ink in a well enough defined fashion for 400DPI to even work, ink spreads out a bit.

Question about resolution of still pix on Canon PowerShot SD30?

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