Precise Cropping

[Andrew Yoole]

Use Image/Canvas Size and type your requirements numerically

[YrbkMgr]

Changing canvas size to a smaller one will force the image to resample according to the settings in Preferences (e.g., bicubic), if I recall correctly. Using the options bar with the crop tool, if you do not specify the resolution, it's a simple (but precise) crop.

[Thee_DarkOverLord]

If you do change canvas size, remember to crop the whole page, other wise you still have active graphics outside of the canvas area, resuliting in larger files than needed.

[Colin Walls]

T_DO:
Can you please explain that further. What do you mean "crop the whole page"? When you change canvas size you always crop. Are you confusing with the "hide" option on the crop tool?

[Thee_DarkOverLord]

probably, yet another retraction from me. I'll get my coat.

[Colin Walls]

T_DO: :-)) [you must be English ...]

[Thee_DarkOverLord]

suits you sir ;-)

[dave milbut]

No no...that would only "warp" the image in this case.




what would?

[Mac McDougald]

Very best way in this situation is use rectangular marquee.
Style: Fixed Size
Type in 760px and 540px
Click on image, move where you want cropped.
Image/Crop.

If you try the same thing with crop tool, you'll invariablly be
interpolating one way or another.

Mac

[Mac McDougald]

No no...that would only "warp" the image in this case.

Mac

[Mac McDougald]

> what would?

Oh, I read that as changing Image/Image Size
rather than Image/Canvas size
(Andrew's post). Sorry.

It would indeed work, although you'd have only the option of taking the
entire "crop" from top or bottom as in original example from OP. The
rectangular marquee method allows you to precisely move it around before
deciding.

Mac

[Phosphor]

Mac...why not just use the Crop Tool in the same manner you prescribe for the Rectangular Marquee?

Hit "OK" after proper positioning and you're done.

[dave milbut]

Oh, I read that as changing Image/Image Size rather than Image/Canvas
size (Andrew's post). Sorry.





I did too at first, then had to revise my post.

why not just use the Crop Tool in the same manner you prescribe for the
Rectangular Marquee?




I'm a crop tool biggot. It's too final. I like to ponder my destructive actions before committing them! :Þ

[Mac McDougald]

> Mac...why not just use the Crop Tool

Because you will not necessarily be cropping only original pixels.

You can pull a tiny area from whole image, and it will interpolate UP to
that to match pixel dimensions you select.

Using rect. marquee will only use original pixels, no chance of
upsampling.

Mac

[Phosphor]

"Because you will not necessarily be cropping only original pixels.





You can pull a tiny area from whole image, and it will interpolate UP
tothat to match pixel dimensions you select."




Not if you don't want to.

I RARELY use the Crop Tool and set it to resize. The only instance I can think of where I've used the Crop Tool that way is when I want to create a specific sized 72 ppi personal avatar for use in a forum from a high-res photo of myself.

[Mac McDougald]

> I RARELY use the Crop Tool and set it to resize.

Phos, the crop tool will in almost ALL situations resample the image, if
you set it for precise pixel dimensions unless you are extremely careful
to make sure the largest dimension is using original border of the image.

In flavor of original example:
you have 800x600 image.
You want to crop to 800x500 image.

ANY crop with crop tool wherein you type 800x500 px will upsample image
unless you ensure your crop border extends to entire outside edge of
image.

If you crop into the image at all to get your 800x500, you are usampling
fewer original pixels back to the 800x500.

This can't happen with rectangular marquee set to fixed size.

Mac

[Phosphor]

Hmmm...

Down I go to the Pixel Dungeon for some research...

[Mac McDougald]

All you have to do to prove/understand with crop tool is:

1. look at original pixel dimensions of image
2. set pixel dimensions at exact same as original
3. crop into image some.

Obviously, if you take less of the picture, using same number of pixels
as you started with, you are interpolating fewer pixels up to more
pixels.

Then do same thing with rectangular marquee.
You'll find you CAN'T make fewer pixels into more pixels as you can with
the crop tool.

Mac

[Mac McDougald]

No,not exactly.

Obviously, you can take fewer pixels than originally with either method.
The trick is knowing at what point you are grabbing fewer *real*
(original) pixels. In your example, if using the crop tool, you could
have selected 1x1 pixel and told it to be 6x6 pixel. But you can't do
this with rect. marquee.

Simplest way to splain:

Make an 800x600 pixel image.
With crop tool, set crop at 800x600 pixels.
You can crop ANY area with that, yes? Even a very small section.
It then interpolates whatever you have cropped to 800x600. Since you only
started with 800x600, obviously it has upsampled.

Now do same thing with rectangular marquee. You'll see that 800x600 pixel
selection can ONLY select the ENTIRE IMAGE. No interpolation possible.
Or grab your 6x6 pixel area out of it, and it will be valid.

The overriding point is that most funtions that folks want to perform
like this, if they use the crop tool to do it, there's a VERY good change
they will upsample actual pixels into interpolated ones. Not possible
with the rect. marquee method.

Mac

[Colin Walls]

Dave:
The crop tool is not necessarily final. You always have the hide option [if you normalise the background layer, you don't actually lose any data at all].