File processing help

[phili1]

I shoot most everything raw except Realty portraits. I never gave it a thought but noticed that when I down load a Raw file and open it in Adobe it opens at a reaolution of 300DPI.

I just notived that my portraits at med fine JPG down loads and opens in Adobe at 72 DPI.

As muc as I know I can not figure this one out.

Anybody with any ideas, as to why.

[Jon]

It's just the camera's built-in settings, and is totally meaningless. You can override the embedded "resolution" at will.

[DaveG]

I shoot most everything raw except Realty portraits. I never gave it a thought but noticed that when I down load a Raw file and open it in Adobe it opens at a reaolution of 300DPI.

I just notived that my portraits at med fine JPG down loads and opens in Adobe at 72 DPI.

As muc as I know I can not figure this one out.

Anybody with any ideas, as to why.

The dpi of the file is unimportant until the document size is included in the same statement. It's like someone saying that the interest on a loan is 10% but there's no indication of how much you are borrowing.

I got into that issue last week when I provided some images to a client. The 20D/10D (and I suspect ALL Canon DSLR's) naturally make 240 dpi images. I'm pretty sure that they do this in order to brag about the bigger canvas size, and the fact that 240 dpi in that size is pretty good.

My client needed H&S shots of herself for the web and mentioned in passing that she needed them 300 dpi. Well these were 8MP RAW files compressed at 12 to become honking big jpegs, so I just left them at 240 dpi. Of course her web person told her that they needed to be 300 dpi so I "fixed" them.

It was my fault for not listening to the client but I sure would have liked to have gotten a hold of the idiot web guy. A) The file has not changed one bit when I switch from 240 to 300 dpi B) If there's a problem with the original file provided it's that its an order of magnitude TOO BIG!!! and C) you will need to make them 72 dpi to go on the web anyway!

In Photoshop's Camera RAW there's a Resolution box where you can specify the dpi you want. I'm guessing that you have something enabled when you process jpegs that creates that 72 dpi. The thing is the canvas at 72 dpi is measured in feet. At 300 dpi it's in inches. In any case just change the dpi to what you want and watch the canvas/document size change.

[phili1]

I know that was what happens, and I know how to change it but I was wondering if there was an in camera setting and as I gather there is not.

Anyway I agree with you and n ot the web guy. The only thing I can think of is he need it because of his compression program. Some sites have there own systen. It is amazing how mnay different approches there are with digital.

Anyway thanks for responding.

[Bodog]

The confusion arises because people continue to incorrectly refer to image resolution in DPI. Images consist or pixels, not dots. The proper Acronym is PPI or Pixels Per Inch. DPI (Dots Per Inch) refers to the size of the dots a printer can lay down on paper (many dots make one pixel). As pointed out in earlier posts, PPI can be changed to any number without changing the size of the image; only the print size is changed. By increasing PPI you're simply telling the output device (printer) to decrease the pixel size, thus a smaller print. Decreasing PPI increases pixel size, thus a larger print. Nothing to do with resolution; the number of pixels has not changed, only the relative size of each pixel. ;)

[phili1]

Bodog I am familar with that and know how interpolation works, what I could not figure out is why when down loading a jpg the output res was 72DPI and Raw downloaded at 300DPI. I thought thnat I was overlooking something in the Camera set up.

[Bodog]

As far as I know a RAW file has no resolution set; it is just raw data off the sensor. During the conversion you can set it to whatever resolution you want. I'm guessing jpegs are set to 72 or 96 PPI by default because the primary use of a jpeg is for viewing on a monitor, as opposed to printing. But that is just a guess. At any rate, the setting is completely irrelevant, as your printer's driver will adjust it automatically when you set the print size.

BTW interpolation is a completely different matter; relating to increasing or decreasing the total number of pixels, not the pixel/inch ratio.

[phili1]

I agree with you thanks for your reply.