Crop affects dpi in Photoshop CS5?

[Z1000]

I'm prepairing big file for printing, A1 format, 7016*9933px at 300dpi. I wasn't completely satisfied with result, so I needed to crop edges a bit, but that affected dpi resolution which changed to 2.5dpi and it allows me to raise it only to 76dpi but I need 300 for printing. Then I've upscaled file to original resolution (7016*9933) because small loss of pixels after croping, and created new document with same resolution on 300dpi and just copy-pasted this 2.5dpi to new 300dpi document, after saving in properties it says 7016*9933, 300dpi and it is in CMYK profile.

Is that ok now for printing?

 

[ALB68]

It should be. Finished size in inches is 7016 /300=23.38 inches x 9933/300=33.11" , that's your original size. I don't think you would have lost any quality in this operation. Did this answer your question?

 

[MrToM]

It seems a very long-winded and drawn out process you've used there but somehow it looks like you've ended up with the result you wanted.

Whether or not you could have had a better quality image without having to up-scale I dunno....but any scaling is generally never a good idea.

It doesn't make sense that 'cropping' changed the resolution....it shouldn't, so quite how you ended up with a resolution of 2.5dpi is beyond me.....unless you scaled it rather than cropped?

Whatever, if it now looks OK then, as Larry pointed out, the final dimensions and resolution should give you a print @ A1 size.

Regards.
MrTom.

 

[Z1000]

This is what PS says when I open file

edit: can't post link, but in image size option it says 300dpi.

I just wondered is it possible to convert 76dpi to 300dpi just by copy/paste into new 300dpi file. Thanks

And I don't know why PS automatically reduced dpi to 2.5

Upscaling is not good, I agree on that, but it was few pixels maybe, without major quality loss, I think it won't be visible on paper.

Sorry for bad English

 

[MrToM]

LOL....your English is fine.....better than some English people!

You may be getting confused with what dpi actually is...

DPI (Dots Per Inch) is NOT actually associated with images on your MONITOR.....this is PPI (Pixels Per Inch)..because monitors have pixels.

DPI is used when PRINTING....(Dots Per Inch)...the 'dots' referring to dots of ink used by a printer (as in the cheap plastic thing filled with extortionately expensive ink).

DPI can, and I stress can, also be used when scaling....if it is changed and the image is marked for scaling then it has an effect. If the image is NOT to be scaled then changing the resolution has no effect on the size of the image but this information gets written into the header meta-data so that when printed the printer can read it and print the image at the correct size.

You can change the DPI as much as you like (without re-scaling on) it doesn't matter.....what it will do though is change the OUTPUT size when PRINTED.....nothing will happen on your SCREEN.

Going back to your example your image already had enough pixels so that when printed using 300dpi would give you an A1 sized print....Larry has shown you the maths for that.

If you then want to CROP some of the pixels out of the image you have to CROP BOTH the width AND the height at the same time....you cannot have different dpi values for horizontal and vertical.

My approach would have to been to just uniformly transform the original image to fit the pixel dimensions of the existing document to fit in the part of the image I wanted......having the effect of cropping those bits I didn't want.

Transforming is still scaling (there is an option to use different algorithms when transforming), so you don't want to do it too much but it has the same effect without changing anything else...

...ratio, fit, dpi, document dimensions, etc etc all stay the same.

That's what I would have done anyway......simply 'uniformly transform' the image to fit the document...so I could see only the pixels I wanted.
No need to copy and paste anything....no need for another document.....simple as.

That's probably confused you even more now and If it hasn't, let me know...I'll try harder.

Regards.
MrTom.

 

[ALB68]

Z1000,
Our forum will not allow a link to be posted until you have 5 posts.
I simply don't understand why you would have dropped to a 76ppi by cropping the image. Inspect your file at a high zoom and look at your edge quality. Hopefully your edges have remained smooth without being jagged. Your going to see some of that eventually with higher zooms but try it about 400% and then maybe 800.

This is what PS says when I open file

edit: can't post link, but in image size option it says 300dpi.

I just wondered is it possible to convert 76dpi to 300dpi just by copy/paste into new 300dpi file. Thanks

And I don't know why PS automatically reduced dpi to 2.5

Upscaling is not good, I agree on that, but it was few pixels maybe, without major quality loss, I think it won't be visible on paper.

Sorry for bad English

 

[Z1000]

I really don't know, It automatically reduce dpi to 2.5 when I crop image and then it allows me to change it at max 76dpi, that's why I approached copy/pasting in order to get 300dpi for printing, that step first came to my mind :mrgreen:

 

[ALB68]

MrTom makes a good point. Where did you see DPI? Photoshop reports PPI for sizes which has a totally different meaning. Again, inspect the edge quality of the image you pasted .

I really don't know, It automatically reduce dpi to 2.5 when I crop image and then it allows me to change it at max 76dpi, that's why I approached copy/pasting in order to get 300dpi for printing, that step first came to my mind :mrgreen:

 

[Tom Mann]

I agree with Larry (ALB) and Mr. Tom that the change in dpi when cropping is *extremely* odd. In decades of working in PS, I've never seen this happen, so I suspect you inadvertently changed the dpi in some other way and only noticed it when you were dealing with the cropping issue.

However, there are easy ways (independent of the dpi number reported by PS) to check if you lost significant amounts of information during the process you described. If so, you would need to go back and correctly crop your image.

For example, I assume that for safety you have been saving different versions of your PSD file as you worked, so you probably have a version just b4 you began the crop related operations, and then another version after all of the manipulations you did.

If so, then simiply convert each version to a JPG (using the same quality factor), and compare the two file sizes. If you cropped away only a few percent of the image, then these two file sizes should be within 10% of each other. If they are not, you've lost more information than you think, and you need to go back, and using a conventional, single step, approach crop your image. If you still can't do this, tell us what happened and we will try to figure out why and help you get through this.

Good luck,

Tom M

PS - The reason I'm suggesting such a seemingly odd way (ie, comparing file sizes) to compare the two versions of your image is that I'm worried that your odd cropping process indeed created a file with the correct pixel dimensions, but has lost more information than just a little bit around the edges. The method I described is a quick and dirty way to tell this that doesn't rely on any dpi numbers.

 

[Z1000]

I've tried it again. It only happens when I crop with certain aspect ratio, if I leave height/width boxes empty DPI doesn't change. And yes it's dpi not ppi, image > image size > and there is the info. If I use certain aspect ratio dpi reduces to 2.407 and it doesn't allows me to change it to 300.

 

[Z1000]

I've compared non cropped and cropped (and after that upscaled version) and there is a difference. Is this going to bi visible on paper, it's ''actual size'' in photoshop

 

[ALB68]

Your screen doesn't look like this?

I've tried it again. It only happens when I crop with certain aspect ratio, if I leave height/width boxes empty DPI doesn't change. And yes it's dpi not ppi, image > image size > and there is the info. If I use certain aspect ratio dpi reduces to 2.407 and it doesn't allows me to change it to 300.

 

[Z1000]

Yes it looks, but I thought that's dpi? I always changed that value for printing and properties says 300dpi. I'm so confused now. Especially with quality loss in comparison above, I've tried to upscale original file for 500px more and there is no major quality loss like in this jpeg.

 

[MrToM]

@ Z1000...

The Image Size dialog box is NOT cropping.
Its 'Re-sampling'. Hence the checkbox called 'Resample'.

If you need to CROP the image as per your original post then do as I have already suggested.
Your image dimensions (in px) are fine, as is the resolution (300dpi)....to give you an OUTPUT (Print) size of A1 dimensions.

To CROP the image use Ctrl + T to enter transform mode.
Hold SHIFT (to constrain proportions) and click and drag one corner handle to transform the image BIGGER.
Do this until the area you want to CROP OFF is outside the document and no longer visible.

Try to keep the dimensions of the transform a multiple of 8....this will give you the best quality.
In other words make the NEW size 7024x9941....OR 7032x9949....etc etc.

The area OUTSIDE the document will not be printed, the document will still be 7016x9933px.

Once you have transformed the image to the area you want use Ctrl + A to select ALL, and then use Image > Crop to trim the pixels outside of the document bounds.

Regards.
MrTom.

 

[ALB68]

Why not use the Crop Tool and just specify the size??

@ Z1000...

The Image Size dialog box is NOT cropping.
Its 'Re-sampling'. Hence the checkbox called 'Resample'.

If you need to CROP the image as per your original post then do as I have already suggested.
Your image dimensions (in px) are fine, as is the resolution (300dpi)....to give you an OUTPUT (Print) size of A1 dimensions.

To CROP the image use Ctrl + T to enter transform mode.
Hold SHIFT (to constrain proportions) and click and drag one corner handle to transform the image BIGGER.
Do this until the area you want to CROP OFF is outside the document and no longer visible.

Try to keep the dimensions of the transform a multiple of 8....this will give you the best quality.
In other words make the NEW size 7024x9941....OR 7032x9949....etc etc.

The area OUTSIDE the document will not be printed, the document will still be 7016x9933px.

Once you have transformed the image to the area you want use Ctrl + A to select ALL, and then use Image > Crop to trim the pixels outside of the document bounds.

Regards.
MrTom.

 

[MrToM]

The crop tool will allow you to make it larger too. I see your point though
Yep...that would do it as well. (darn, why didn't I say that?)

Regards.
MrTom.

EDIT:

I didn't say that because using the CROP tool will change your document size.(Dimensions)
Transforming the image will keep the document size and resolution but 'Crop' the image within it.

 

[Z1000]

I am using crop tool. And than ppi changes, and I need to change it to 300 if I want to print document but PS doesn't allows it after using crop tool

 

[ALB68]

OK. Let's back up a bit. The original document..when you look at the Image/Size screen, what is the PPI? Communication is breaking down or something.

I am using crop tool. And than ppi changes, and I need to change it to 300 if I want to print document but PS doesn't allows it after using crop tool

 

[MrToM]

I am using crop tool. And than ppi changes, and I need to change it to 300 if I want to print document but PS doesn't allows it after using crop tool

Well try my way instead....you'll keep the document size AND the resolution.

Regards.
MrTom.

 

[Z1000]

OK. Let's back up a bit. The original document..when you look at the Image/Size screen, what is the PPI? Communication is breaking down or something.

It was 300, then I cropped it and it changed to 2.5, then I created new 300dpi(or ppi) document and copied this 2.5ppi on it, saved it and now it says 300dpi (7016x9933px) in properties of document. Can I send it for printing?

Anyway I found quality loss reason, it's because of action I used on final jpeg file, didn't notice it earlier.