Hi Jacob,
Ok, I've chosen an image that is 3508px x 2631px and is 300ppi.
I've opened a new artboard sized at the above size and placed the image into the artboard.
Going to the transform panel it shows that the placed image is 841.92px x 631.44px. and says that at this size it is 300ppi. These figures, when multipled by 72 become 60618.24 and 45463.68 so nothing like what I want them to be. However when divided by 24 and multiplied by 100 they become the correct 3508 x 2631. So the placed image is effectively 24% of the size I want it to be and at this smaller size it is 300ppi. However...
Once I resize it to 3508px x 2631px using the transform panel the resulting image is showing as 72ppi in the documnet info panel! Even though the original image is 300ppi at these dimensions! I just can't work out why?!?
mrplod,
Ah, now I know what you mean.
Illy basically works in points, 1 point = 1/72 inch, and the unit pixel (which you can choose instead of points, inches, etc) is set to the same value, 1/72 inch. This ambiguity is part of the difficulty in grasping all this.
I've chosen an image that is 3508px x 2631px and is 300ppi. |
An image that is 3508px x 2631px is just that: this is the pixel size, meaning that it is made of 3508 x 2631 = 9,229,548 pixels (small squares), each of which may have its own colour, no more, no less.
This image can be represented at any size in any application, and that size will determine its resolution in PPI (Pixels Per Inch). If you divide the size by 300 to get a resolution of 300 PPI you will get 11.693 x 8.77 inches = 841.92 x 631.44 points/pixels (understood as the unit 1/72 inch).
This means that if you want the image to have a resolution of at least 300 PPI you cannot make it larger than 11.693 x 8.77 inches = 841.92 x 631.44 points/pixels (pixels as units in Illy).
If you want a larger image at 300 PPI you will have to start with a larger original image.
An image fitting an Artboard of 900 x 900 points/pixels = 12.5 x 12.5 inch at 300 PPI will have to be 3750 x 3750 pixels (300*12.5 = 3750).
Are you sure that is the actual size of the red square you made in Photoshop? If so, I have no clue why it shows up the way it does in Illy.
Edit:
I just reread this:
I then saved this image as a jpeg so the jpeg had a dimension of 900px x 900px |
When you export as a JPEG, you can set a resolution, but you can also just save it at an actual pixel size (as in Save for Web & Devices) such as 900 x 900 pixels. Maybe that is where things go wrong.