I guess what I am really confused about is the Wiki documentation for imageJ's aspect ratio.
"
To set the pixel aspect ratio, measure the width and height (in pixels) of a digitized object with a known 1:1 aspect ratio. Enter the measured width (in pixels) in Distance in Pixels. Enter the known width in Known Distance.
Then calculate the aspect ratio by dividing the width by the height and enter it in Pixel Aspect Ratio."
If it has a 1 to 1 aspect ratio, won't the pixel aspect ratio just be 1? What is width/height actually calculating? Won't it be calculating the Storage Aspect Ratio?
I'm new to the details, so I'm getting all my information from this Wikipedia excerpt:
"The ratio of the width to the height of an image is known as the aspect ratio, or more precisely the Display Aspect Ratio (DAR) – the aspect ratio of the image as displayed; for TV, DAR is traditionally 4:3 (both analog and digital), with 16:9 (widescreen) now also common. In digital images, there is a distinction with the Storage Aspect Ratio (SAR), which is the ratio of pixel dimensions. If an image is displayed with square pixels, then these ratios agree; if not, then non-square, "rectangular" pixels are used, and these ratios disagree. The aspect ratio of the pixels themselves is known as the Pixel Aspect Ratio (PAR) – for square pixels this is 1:1 – and these are related by the identity:
SAR × PAR = DAR.
Rearranging (solving for PAR) yields:
PAR = DAR/SAR."
I see changing the aspect ratio drastically changes the results of the measurements, so I really need to get a full understanding of what's going on behind the scenes.
Ravi Vaidyanathan wrote
Hi,
I would like to know how an image is being displayed in ImageJ. I have a 256X256 image that corresponds to a real world field of view of 2.3 mm by 1.4 mm. How does ImageJ display it and adjust the aspect ratio?
Thanks and regards,
Ravi
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