Digital Light & Color

A question, or two, about resolution.

Both "New Image" and "Layout" have Resolution(dpi) as choices (other operations may have this as well, but I noted it for these two operations which I just recently did on a couple images).

- I understand the correlation between units of measurement in the Layout Transform as it pertains to dpi (shouldn't it be ppi?). I was placing a 7000 x 5000 image into a 10000 x 7000 layout and, depending on the dpi, the inches or cm would change. Of course, if in pixels, nothing would change if the dpi was altered. I usually set the units to pixels, as I don't need to know inches etc.

However, my (first) question is, it appears the default dpi is set at 100, but I usually set it to 300 (not sure why, just a habit I've gotten into I guess), and when I eventually press the "OK" button, I see the Resample dialogue come up and briefly count down. What is the purpose of this dialogue and exactly what is being resampled? The resultant image is, as expected, 10000 x 7000 pixels, so why the Resample?

- "New Image" also has a Resolution(dpi) that can be changed, but it appears to default to the resolution (and size and colour bit) of an image that is open and active. For an on screen image only (as opposed to an image about to be printed), what is the purpose of this setting when generating a new image. If I recall, the print dialogue has the ability to change resolution when printing, so I don't understand the need for dpi resolution when merely generating a new image.

- When compositing two images with different resolution, am I correct that the Input Image controls the dpi (actually ppi)?

- And last, it appears that masks have a default resolution of 100 ppi, regardless of the ppi of the image from which the mask was generated. Is there a particular reason for this?

Thanks in advance,

Marv

The resolution setting can be thought of as a hint for how large to make the image in physical units. It has no effect on any of the image processing operations, so the value you set for example in New Image does not really matter except in certain special cases such as printing to image dimensions or defining the default size when importing an image into a Word document. In Layout, if you specify the image size in physical units, the dpi setting determines the width and height of the output image in pixels, so it does matter there. If you specify the size in pixels, the dpi setting does not affect the output image. Layout resamples all images to fit in their respective panels. I am working on a new version that lets you specify panel size as image size, either in pixels or physical units, but that is not released yet.

You are right - it should really be ppi and not dpi, but dpi had become common parlance.

Generally the output dpi is set to the input dpi setting by most transformations.

No reason for 100 dpi for masks - the value is arbitrary.

Jonathan,

Thanks for the quick and informative reply.

Marv