I was wondering how can I make an image stay 12mp and 300dpi. I want to participate in a contest about street photography but their requirements are that the image must be 12mp and 300dpi. I'm new to photography and I'm confused about the dpi and the image resolution at 12mp. Also if its okay to shoot at RAW for this case? And would I be able to edit in lightroom the image? I'm using a canon t5i rebel efs 30-135mm. Thanks guys! Appreciate all the tips and advices.
Dpi is dpi and megapixels are megapixels.
Apples and oranges. These are two different values that can be chosen independently.
12mp means that the total number of pixels should be 12 megapixels. Your camera is capable of shooting images with more megapixels so you might have to reduce the size of the image so that it is 12mp.
300dpi means that the resolution should be set to 300 dots (pixels) per inch. This is only relevant for print.
Also if its okay to shoot at RAW for this case?
This is yet another entirely unrelated thing. You have read the contest rules. It would be very odd if you were not allowed to use RAW, because you likely have to send in a common file format like .jpeg and nobody knows what intermediate formats were used. Also, there's always RAW involved, whether the conversion happens in camera or in post production doesn't really change that.
And would I be able to edit in lightroom the image?
Again, read the rules of the contest! If they have no restrictions about image editing you can do whatever you want. But as it is a street photography contest, I'd guess that only minor image adjustments are allowed and major image manipulations are not ok. But as I stated previously: this is all up to the contest and you simply have to read the rules.
If you are unsure, just send them an email and ask.
Your camera is 18Mpx. 12 is a smaller one.
For an important shoot get used to shoot in RAW so you have flexibility to edit the image, but it is not important for the requirements of this contest.
You could just shoot at your max resolution and resample later from 18 to 12 with any editing program. Photoshop or Gimp. You can asign the 300 ppi in the same process.
You said "stay 12mp" so I assume the image is 12 mp now.
So in Lightroom, in the Adobe Camera Raw editor view, there is a line of text immediately below the preview picture. That line (by default) begins "sRGB", and ends with "ppi". Just click that line to change the values, and you can set it to 300 ppi. Then the JPG that you save will be that size (still 12 mp) and will say 300 ppi.
If not 12 mp now, you can resample it this same way. HOWEVER, changes here will apply to all future image processing too, so in some cases, you may want to change it back to original values when done. You surely don't want to resample all future images this way. But to do it, a 12 mp DSLR image will be approx 4243 x 2828 pixels in size.
The 300 dpi specification is totally meaningless, the image size in pixels is the only size it has. But many contests do stupidly say "300 dpi" anyway, not knowing how things actually work, and it is easy to satisfy them this way. Just tell them 300 dpi.