Crop Tool Doesn’t Resample

S
Posted By
Scanman
Aug 6, 2004
Views
522
Replies
20
Status
Closed
I have alot of images (bitmap) that I need to change the resolution from 600 to 300, but leave the image size the same. I SWEAR I used to simply input those numbers in the crop options, and the tool would resample (throw away the info) and leave the image the same size.
When i do this, it resizes the image, which means I then have to resize. any ideas ?..Is this "a feature, not a bug?"

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CB
charles_badland
Aug 6, 2004
So you enter the current Width and Height AND the new ppi in the crop tool option bar? Don’t confuse the image shrinking on your monitor (after cropping) with the physical dimensions assigned to the photo changing.
and
If all you want to do is resample (not crop out any part of the image), wouldn’t it be easier and faster to record an action using the Image Size dialog box to resample from 600 ppi to 300 ppi?
cb
S
Scanman
Aug 6, 2004
I leave the width and Height blank, and just enter the new ppi……
CB
charles_badland
Aug 6, 2004
Well, it’s interesting: If I enter only ppi in crop tool using Photoshop CS it resamples, but on PS 7, it resizes without resampling. You don’t say the version you use…
But that aside…
can’t you just enter the dimensions along with the ppi and have it work? Or record an action?
CC
Chris_Cox
Aug 7, 2004
Bitmap images can’t be resampled (because there is only black and white).

You have to convert them to grayscale to resample.
CB
charles_badland
Aug 7, 2004
Chris, I can… no real type of interpolation. But I can certainly add or throw out pixels in a bitmap (1 bit) image in Photoshop.
cb
JS
John_Slate
Aug 7, 2004
….so can I Chris.

What do you mean?

Charles: Try resetting/deleting you preferences.
CC
Chris_Cox
Aug 9, 2004
I mean what I said – you can’t resample bitmap images.
Throwing away pixels would mean a simple crop (cutting off the edges).

You were asking about a resample (although it’s difficult to figure out what you meant from your description).
CB
charles_badland
Aug 9, 2004
Chris,
Why then, if I create or open a bitmap (1 bit) file, can I go Image>Image Size, select Resample and add or subtract pixels. Isn’t that resampling a bitmap image?
cb
CC
Chris_Cox
Aug 10, 2004
Hmm, all resampling commands are supposed to be disabled for bitmap images.
R
Ram
Aug 10, 2004
Well, I just converted an image to grayscale first, then to 1-bit bitmap, and upsampled it by 400%. Not pretty at 100%, but something is happening. Yet viewed at 25%, the upsampled image looks just like the original.
MO
Mike_Ornellas
Aug 10, 2004
The issue here is that the interpolation setting should be "greyed" out.
R
Ram
Aug 10, 2004
Someone forgot to gray it out. 🙂

Maybe the same person who forgot to delete Adobe Gamma before burning the Photoshop 7 Mac install CD.
CB
charles_badland
Aug 10, 2004
Mike and Ramón
You don’t mean that the selection to resample should be grayed out under Image Size…right? .. just the interpolation choices in preferences.

I mean, you can resample a bitmap by adding or throwing away pixels.

If I create a bitmap file 1000 X 1000 px with a nice big black circle (grayscale first then convert to bitmap) then resample down to 25 X 25px, you can it does reduce the number of pixels. The black circle becomes obviously pixilated. I get a small file.
So resampling is taking place…. PS is deciding which new pixel should be black and which one white.
CC
Chris_Cox
Aug 10, 2004
You can’t really resample a bitmap – there is nothing between black and white (because those are the only 2 values available).

Yes, resample should be disabled in ImageSize.
R
Ram
Aug 11, 2004
Yes, resample should be disabled in ImageSize.

Yup; when I tested it earlier today, the resampled b&w image (resampled from 72ppi to 288ppi) viewed 100% looked identical to the original viewed at 400%. The image got bigger, but it didn’t get resampled, just amplified.
CB
charles_badland
Aug 11, 2004
Well, so this boils down to semantics? If “resample” means you can add or subtract pixels from an image, then it should NOT be grayed out. (so just how far off thread are we?;)

If the pixel dimensions is changeable in Image Size, then that is resampling. (right?) And there IS interpolation if you downsample. My point is that PS does allow resampling (ie changing the number pixels making the image) so it there is no reason for it to be grayed out.

Really, I’m not trying to be obstinate, it just seems like resampling is taking place here.
R
Ram
Aug 11, 2004
Charles,

Take a regular 8-bit image, duplicate it, then resample the copy by a factor of four. Now view the original at 400% and the copy at 100% side by side. See the difference? That’s resampling.

Now take a 1-bit b&w image and go through the same exercise. No difference between the original at 400% and the copy at 100%. No resampling. Each pixel in the original just got enlarged by a factor of 4.
CC
Chris_Cox
Aug 11, 2004
No, resample means determining the value of pixel between existing pixels (or groups of existing pixels). This usually involves interpolation (which is impossible in a bitmap).

It’s not semantics so much as quality.

No, ImageSize is not resampling – it is sampling the image without interpolation , but not very well.
CB
charles_badland
Aug 11, 2004
OK. Y’all make sense. (i’m in Florida) But a user can take a 1000 x 1000 px bitmap image and reduce the image to 100 X 100 px. Which I believe gets back to the original post…
R
Ram
Aug 11, 2004
Charles,

a user can take a 1000 x 1000 px bitmap image and reduce the image to 100 X 100 px.

That’s simple reduction, not true resampling. Enlarging is not the same as upsampling either. If you have an old copy of SuperPaint, try it and look at the difference. 🙂

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