Photo Definitions

I've been in photography for the last 40+ years. Lately I have seen Uprezzing and  downrezzing ( forgive spelling) and I'm not sure what they are talking about.
Is it another way to say cropping or are they saying they are changing the DPI setting. I tried looking it up but all I found was about video.
I do all my own printing so the DPI is set all the time at 300.

Thanks for reading
Larry

Lets say you have a photo that natively is 6000x4000 from a 24 megapixel camera. Yu take one of those pictures and you make it 1200x800 for posting here on NSN - that's downrezzing.

Now if you take that same 6000x4000 image and change it to get a 300DPI print at 30x20" you need 9000x6000 pixels. When you change the size to 9000x6000 that is uprezzing.

Why wouldn,t I just crop it to the correct size? Last May I opened a Cape May shot and cropped it to 24x36 at 300DPI.
How is that different from your 2nd paragraph? Or is just a different way of getting to the same place?

Larry

Cropping is removing part of the photo, e.g. some off of one side or top, or both, etc.  You do have smaller pixel dimensions, but that's not down-rezzing.  If you used the whole frame from a camera that has a 2:3 ratio sensor, then you didn't "crop" to make it 24 x 36 at 300 ppi, you up-rezzed it:  24 x 300 by 36 x 300 = 7200 x 10800 pixels.

Larry Shuman wrote:Why wouldn,t I just crop it to the correct size? Last May I opened a Cape May shot and cropped it to 24x36 at 300DPI.
How is that different from your 2nd paragraph? Or is just a different way of getting to the same place?

Larry

That's not cropping.  You may have used the crop tool to resize to your new dimensions but the action it is performing when you do that is a change in resolution.  Cropping is the act of removing a portion of the picture.  I think you are mixing up the name of a tool with what is actually being done to the photo.  The crop tool in photoshop has the capability of doing things that aren't really cropping - it has a resizing capability built in.

Larry Shuman wrote:Why wouldn,t I just crop it to the correct size? Last May I opened a Cape May shot and cropped it to 24x36 at 300DPI.
How is that different from your 2nd paragraph? Or is just a different way of getting to the same place?

Larry

Answering your original question-it's basically changing resolution up or down.

Now with crop example it's a little bit more complicated. If you use crop tool and only change
resolution settings before applying crop tool you're basically cropping and changing resolution but that changed resolution
affects only document size for printout.

If you however change resolution (to higher) and type in width or height before applying crop tool then you're basically (most likely)
uprezzing-assuming your source is low resolution.

In the end if pixel size in Image->Image Size command is higher-you're uprezzing,if lower-you're downrezzing no matter what you did with crop tool.