If I convert my file to PSD to JPEG, does it remember the width and height of the picture?

Question

So I'm doing some card invites on my computer. I'm using photoshop, and I've got it with the height and width that I want to print it out.

The only problem is, I'm going to have to take the file to a computer that doesn't have photoshop in order to print it out. So I've converted it to a JPEG on the best quality.

THe only problem is the JPEG format doesn't seem to store the dimensions in the meta data. Like my PSD file seems to have width = 95mm and height = 145mm but the JPEG's metadata only has the number of pixels of the width and height.

Is that enough information? I thought pixels were different sizes for different computers and printers right?

So can anyone tell me, if I convert a PSD file to JPEG, does it maintain the print size of the image? If not, can anyone tell me a better file format i should be saving my files into.

Answer 1

JPEG files don't know anything about "size" other than the pixels they contain. If your PSD file is 95 × 145mm, and you want to save it in a pixel-based format (like JPEG), you have to think about how many pixels per millimeter you want to store.

Or, in professional terms, "dots per inch". Or, when we're talking about doing this on the computer: "pixels per inch" (there are no dots in a computer).

Typically, when aiming for printing, 300 PPI should be enough to maintain good quality. Therefore, set it accordingly when creating the file:

If you now save that as a JPEG, it will have a dimension of 1122 × 1713 pixels (let's skip the math here). The important thing is: Your image was still made with a resolution of 300 dots per inch (for printing). So, you're good to go.

There might be a possibility where the DPI metadata in the Exif tags of the image are incorrectly interpreted:

That this picture is not 72 dpi, is visible when you look at Windows Explorer or Windows Viewer. The Exif (properties box) mentions here 96 dpi. So Photoshop invents 72 dpi, and Windows thinks: let’s make it 96 dpi.

In this case, the pixel size is still right though, so you may have to adjust the print size. The metadata could be wrong there. What matters is the count of pixels you have.

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That all being said, choosing JPEG for vector graphics like text and hard edges is bad. JPEG was optimized for photos with smooth transitions. With text—unless you choose really high quality—you might see weird artifacts on edges.

Therefore, you should save the image in an uncompressed format, like PNG or TIFF (where the latter also supports the notion of image "layers").

Answer 2

Did you export to JPEG as opposed to 'Saving As' or 'Save for web and devices'? That's always the best option, maintaining the highest DPI available which is usually 300.

Here's some more info: http://gophotoshop.tribe.net/thread/bee88c85-8e09-41fe-b6f6-183a91338b79#453fde65-fa52-4fdc-80f6-9ec3d394dbb2