cropping

[Sabina]

Hi everyone ~ I recently heard that it is a bad idea to crop a picture using crop tool - that it resamples the entire photograph each time a crop is done. Is this true? If so, what is a better tool to use in cropping?

Also, I frame my photos using crop, bring the cropping box out a bit from the edges of the picture and selecting a colour for the frame - in other words, I'm not removing any of the picture, I'm adding to it. If cropping causes resampling, does making a frame the way I do, cause resampling as well?

Thanks for any help ~ Sabina

[symes]

Anything you do to a Jpg in Photoshop or any other program causes it to lose a little bit of Data. I haven't noticed it, but I am also not a Pro...

To avoid this use a tiff file while you are still working with a photo and then convert to jpg when all changes are done.

So convert from RAW to Tiff, work on it and then when you are finished convert to JPG.

Cheers,

[Sabina]

Thankyou Symes, much appreciated!

[tim]

Anything you do to a Jpg in Photoshop or any other program causes it to lose a little bit of Data. I haven't noticed it, but I am also not a Pro...

I don't think this is as clear as it could be. Once you load a JPG into Photoshop, it stores an internal representation, and all operations inside photoshop are lossless (except if you do something like a blur etc). You only lose data again if you save as JPG again.

[lostdoggy]

I don't think this is as clear as it could be. Once you load a JPG into Photoshop, it stores an internal representation, and all operations inside photoshop are lossless (except if you do something like a blur etc). You only lose data again if you save as JPG again.

That is not exactly clear either. Whenever you open up a JPEG file and then save, it will lose data. You don't have to do anything to the picture. This is because the JPEG file is compressed in a lossy compression and needs to be expanded in order to be used. when you terminate the session and save you have to recompress it again in a lossy compresion. But if you terminate without saving the original file is unaffected.

[tim]

That is not exactly clear either. Whenever you open up a JPEG file and then save, it will lose data. You don't have to do anything to the picture. This is because the JPEG file is compressed in a lossy compression and needs to be expanded in order to be used. when you terminate the session and save you have to recompress it again in a lossy compresion. But if you terminate without saving the original file is unaffected.

Sure. May I try again? The only thing that will lose data is saving a file as JPG. Operations inside photoshop don't degrade the picture, unless the action you take is destructive.

[mgbeach]

if you save as another copy then the quality of the original image you opened is unaffected, correct?

[tim]

Yes.

[lostdoggy]

Sure. May I try again? The only thing that will lose data is saving a file as JPG. Operations inside photoshop don't degrade the picture, unless the action you take is destructive.

Sorry didn't mean to trump you!!!

[tim]

Just trying to put things clearly, i'm not the best technical writer around :)

[lostdoggy]

Neither am I
I write like I studder!!!

[jfrancho]

Just trying to put things clearly, i'm not the best technical writer around :)I'm not the best reader, I thought the thread title was for something else....

[Sabina]

LOL jfrancho, unfortunately I think I can figure out what you mistook my title for.....

soooo..... does anyone know why a person would use 'select' to crop, instead of crop tool? The person who told me this, said it's because cropping with crop tool resamples the entire pic. Does that sound right? If so, what about making frames with crop tool? Does this resample the pic as well even though I'm not cutting off any part of the pic?

[lostdoggy]

Sorry, well me let take a try at this.
Let say your original file was 8X10 at 240ppi and then you want to crop out say 80% of the image set at 8X10 at 240ppi. So now you have taken 20% of the image away but the final image which still have the same final size. In order to do that PS will have to add pixels to fill in the missing 20%. To do this PS will resample the picture. To minimize the resampling the cropping would have to be smaller then the original.

[Sabina]

ah ha,,, I see. Thankyou very much.

[alfa1six4]

If you still want to use the crop tool and not resample the image, just leave the vertical, horizontal and resolution fields blank at the top of the screen. All the pixels outside of the selection will be tossed out.

[tim]

Here's something else - now when I choose the crop tool in CS2 it crops to a specific number of pixels, not a specific ratio. Anyone know how to get it back to a ratio?

[jfrancho]

Here's something else - now when I choose the crop tool in CS2 it crops to a specific number of pixels, not a specific ratio. Anyone know how to get it back to a ratio?In the crop tool, you can specify pixels (px) or inches (in). I'm pretty sure you can change the unit of measure in Preferences. Is that the answer you were looking for?
Anyway, I usually only crop in ratios, for making different print sizes, so I'm really not losing much. I also crop the psd file, create the jpeg from there. I assume that is a preferred way. Does anyone know if it would be best to crop in ACR? I'm guessing it would be the best way on paper.

[tim]

I can't see a preference for that :( Anyone else know how to change the crop tool from pixels to ratio?

If you open from RAW then you might as well crop in ACR, I don't think it'd make any difference though.

[Sabina]

What about if you're just cropping a pic by selecting crop tool, and doing the crop - without selecting any ratios or dpi's or anything. For eg. say my picture has some unwanted junk on one edge, that I wish to cut off, I select 'crop tool', move my mouse cursor along the unwanted edge to bring it further in, and crop that off. I'm not specifying anything at this point, just getting rid of the unwanted edge. Is this a mistake? Does this resample the rest of the picture?

[mgbeach]

I can't see a preference for that :( Anyone else know how to change the crop tool from pixels to ratio?

If you open from RAW then you might as well crop in ACR, I don't think it'd make any difference though.
The Lights Right Studio has a great selection preset available that I've attached here. It has common print sizes in both portrait and landscape.
I hit Alt+Ctrl+I to bring up the Image Size menu and change the resolution there. Then I use one of the selection tool presets to drag out the area I want. Then Image...Crop and I'm done.
download and unzip the file. Then put it in the presets folder under Photoshop. select the Marquee tool and then Load Presets. Browse to the file and you're good to go.
Wow, that probably sucks as far as directions go, but you should be able to figure it out

[prime80]

When you don't set a ppi in the dimensions, the crop is not destructive. The only time the image is resampled during a crop is when a ppi is entered in the top toolbar.

[tim]

What about if you're just cropping a pic by selecting crop tool, and doing the crop - without selecting any ratios or dpi's or anything. For eg. say my picture has some unwanted junk on one edge, that I wish to cut off, I select 'crop tool', move my mouse cursor along the unwanted edge to bring it further in, and crop that off. I'm not specifying anything at this point, just getting rid of the unwanted edge. Is this a mistake? Does this resample the rest of the picture?

No.

[Sabina]

Thanks Tim.

[tim]

I think this comes down to understanding basics of digital photography, I think I can help. Pictures are just numbers put in rows and columns, ie an array, like this

1 4 6
2 3 5
9 2 4

If you crop a photo, all you're doing is taking away some data. For example, if you crop so you keep the top right part of the image, you'd have this.

4 6
3 5

Taking away data doesn't alter the data that's already there. Of course real images have many more numbers, and the numbers are bigger. A 16 bit image on high res from a 20D is 3504 x 2336 numbers, and each number is between zero and 65000 or so. For an 8 bit image the numbers are between 0 and 256

Some operations are destructive, like changing levels. If you have an 8 bit image, one value might be 197. If you increase the levels by 8% it comes to 212.76. Photoshop has to round this to 213 because otherwise it can't store it, so you lose all little data. When you're in 16 bit more you lose less data, percentage wise.

Hope that helps, and makes sense.

NB: I have skipped over some details to make this simpler, there's no need to correct any picky details I have wrong, unless they're major. For example, I know that depending on how things work under the bonnet it might be a three dimensional array, each array position containing R G and B values, CMYK, etc.

[Sabina]

yes is does (helps, and makes sense),, I just learned that bit about levels being destructive. I never really liked using it anyway, I prefer to use curves (I *think* curves is non destructive...?).

[tim]

Curves is destructive, same as levels, as it changes each pixel by a variable amount. It's possible you might lose a little less data when the curve is a straight line, but I wouldn't bet on it. If you operate in 16 bit mode it's not too important, it's more important to get the picture looking right :)

[Sabina]

arg! Okay, well I guess all of this destructiveness is a good thing to remind a person to get the picture as near correct as they can when they actually take it in the first place, lol.