ChrisO wrote:
Hi Rod - can you translate for me? I haven't the faintest idea what any of that means I'm afraid...
Thanks,
Chris
Physical Pixel Dimensions (pHYs)
The pHYs chunk encodes the absolute or relative dimensions of pixels. For example, an image scanned at 600 dots per inch has pixels with known, absolute sizes--namely, one six-hundredth of an inch in both x and y directions. Alternatively, an image created on a 1280 × 1024 display will have non square pixels, and the relative dimensions of each pixel, also referred to as the aspect ratio, may be stored so the image can be displayed as it was intended to be seen.
To get the code translated to actual pixel width we will need ofnuts help.
For a GIF you would take the 2nd number multiply that by 256 and add the 1st number for a width. Then you would take the 4th number multiply that by 256 and add the 3rd number for height.
This doesn't work in this case for your PNG format. The results would be far to wide and tall.
For a GIF the example would be-
Example: "47 49 46 38 39 61 96 01 57 02" The width is the 7th and 8th bit, but the numbers are reversed. For GIF, take the 8th bit (01) and multiply by 256, then add the 7th bit (96). Gives you a width of 352. The height, take the 10th bit (02) and multiply by 256, then add the 9th bit (57) to give you 569.
When i go to Image>Print Size in Gimp i get these dimensions which seem correct.