Sorry for the delay in response @szh141 …
Just a few thoughts - and perhaps others here on the forum can provide you more guidance …
I worry that the images you present cannot be used to reliably measure what you wish to. Some issues include:
Using bright field to delineate your cells. Ideally you would have a membrane marker in this case, as you want info regrading distance from cell periphery - you need a membrane marker. You cannot use bright field to define the cell membrane unfortunately. Also - with the images you have, overlapping cells cannot be distinguished from each other - so this may cause issues if you want per cell measurements.
Using widefield images for these measurements. Because you are also interested in distances… and need to measure those reliably within each cell - it would be better to use confocal images - so you have an optical sectioning of your cells - will also be easier to delineate individual cells and their membranes.
(Would also recommend acquiring 12- to 16-bit images for intensity measurements…)
This is not to say all is lost. You could perhaps extract some preliminary data… but perhaps you need to approach again your experimental set-up along with refining what you need to measure accordingly. Perhaps others have better insight. But I would point you again to the Principles page of the ImageJ wiki.
If you have more questions/comments - please do post again.