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Old 11-01-2010, 04:55 PM   #1
Shoalwater17
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Question Question about cropping and image size.

I have about drove myself crazy trying to figure this out. I'm using Photoshop Cs5 and as any photographer knows you have to crop photographs at times for the desired effect. Let's see if I can explain this. If I want to crop a photo but keep the original pixel dimensions, can this be done? What I'm finding is when I crop (in PS or Camera Raw) the pixel size is reduced as well as the file size. I know the file size will be reduced and I don't care. The problem I see when cropping is when cropped, the file can reduce to something like "1200 x 800 ppi". This is fine for computer viewing but what if you are trying to submit to a stock photo site? They have minimums for uploads and cropped images are often less than these minimums, usually 1600 x 1200 and/or 2MP. It's always (I think) better to upload a photo close to it's original size if possible. I hope this makes sense.

Thanks in advance.
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Old 11-01-2010, 05:56 PM   #2
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When I submit images in a gallery to MaxPreps, they require that the images be 1600 x 2166 x 300 ppi. That way, customer can purchase prints from 4x6 to 16x20 and not lose any of the image due to cropping to the desired size.

So, in Lightroom, once I finish tweaking the images, I export them and resize them to the 1600 x 2166 x 300 ppi. That usually makes an image of about 2mb in size.
Does this help?
Mike
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Old 11-02-2010, 12:04 PM   #3
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Shoalwater,

When an image is cropped, what you are doing is drawing a box around the part of the image you want to keep, and discarding all the pixels that are outside the box. Thus the pixel dimensions of what you have remaining will be equal to the dimension of the crop box, and always smaller than the original.

In the attached example, the original image is 5184x3456 pixels and the crop window is 2724x2043 pixels. After I throw away everything outside the crop window, I'll be left with a JPG that is 2724x2043 pixels in size. If I save the cropped JPG to disk, the file size will be a function of the pixel dimensions and the JPG compression factor used.

The term "ppi" (pixels per inch) or "dpi" (dots per inch) are synonyms. Both terms are meaningless while the image is being viewed on a computer screen. Screen dimensions are measured in pixels, not inches, thus the only relevant dimension to your image must also be measured in pixels. DPI or PPI only becomes relevant when the image is placed on or is being prepared for placement on something where the dimensions are measured in inches... namely paper.

Generally speaking, to obtain "photo quality" prints, the image should be printed at 300dpi. Thus to get a 300dpi 8X10, I must send the printer an image that is 2400 pixels x 3000 pixels. If I specify that same image be printed at 4x5 inches, the pixel density will be 600dpi. If I specify it be printed at 16x20 inches, the pixel density will be 150dpi.

If I print the example cropped image at 300dpi, the hard copy print will be 9.08 inches (2724/300) by 6.81 inches (2043/300). I can get a larger hard copy print from that image, but the pixel density will be less than 300dpi and the quality of the print will be less. If the hard copy gets too large and pixel density gets too small, you begin to see pixel "stair stepping" in the print.

CS5 gets a little confusing here, because it wants to know width and height of the crop window in inches with a specified resolution. That's because CS5 is assuming the image is destined for paper. CS5 isn't very friendly if that image is destined for a web page where dimensions must be measured in pixels rather than inches. In this case, the user is required to do a little arithmetic. Be assured, that in CS5 if you specify the crop window to be 4x6 inches at 300dpi, the pixel dimensions of what you will end up with after the crop will be 1200x1800 pixels. You could tell your printer to produce an 8x12 print from it (twice the size), but if you do, the density will only be 150dpi (half the density).

In Mikes example of 1600 x 2166 x 300 ppi, if that image is printed at 16x20 inches, it will be printed at close to 100dpi. It will also be distorted because 1600x2166 pixels is a different aspect ratio than 16x20 inches. If it's printed at 300 dpi, it will be 1600/300=5.3 inches by 2166/300=7.22 inches.

Dick
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Last edited by Formula4Fish; 11-02-2010 at 12:22 PM.
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Old 11-02-2010, 04:44 PM   #4
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Mike and Dick, thank you very much for the reply. Your posting helps to an extent, it can still be confusing. I know and have used the PS "Save for WEB and Devices" function as well as the "Save to Hard Drive" Export function in Bridge. Those are pretty straight forward. The "Image Size" function under Image button is where it gets confusing. It has sections for changing pixel dimensions, Document size as well as resolution. Then you add the buttons at the bottom for "Scale Styles, Constrain proportions, and Resample Image it get overwhelming. I know it's a big no-no to Up-Sample photos as you cannot ADD pixels that were not there in the first place. I guess I just have to make sure that when I "crop" a image it never goes under 1200 x 1600.

Thanks again guys for your help.
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Old 11-02-2010, 04:57 PM   #5
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I think your query...and the excellent responses...tell the tale of why BIG, LONG and expensive lenses are made and sold daily.

If just anyone could take a far away shot, and then crop it and still have a really good detailed image...then...no one would need to buy the big, long lenses.

Cropping is great to select out a portion of the shot. It often makes a poor shot into a good shot..by eliminating poor backgrounds etc. It is not a good substitute for a long, sharp lens, though.

regards, Rich
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Old 11-02-2010, 06:29 PM   #6
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Shoalwater,

After you have worked on your image in CS5 and are ready to save it, I suspect you should be using "Save As..." rather than "Save for Web & Devices..." See attachment.

Once you have saved it in CS5 using "Save As...", you're done! You can then click on "Close and Go To Bridge..." and Bridge will be displaying the image you just saved. There is no point in using the Bridge function "Export to Hard Drive." to save it again. It was already saved on your hard drive by CS5.

Basically, Bridge is for browsing your images and PhotoShop is for modifying them and saving the modified images. The workflow could be:
  • Browse your images with Bridge
  • Select an image to be worked on, double-click it to open it in PS
  • Make the desired changes in PS and "Save As..." to save those changes. Here, you might assign it a new name so you never alter the original... such as the original is "MyPicture.jpg" and the modified copy is saved as "MyPicture_cropped.jpg".
  • Then select "Close and Go To Bridge" if you wish to go back to Bridge. In Bridge, you will see the original "MyPicture.jpg" AND MyPicture_cropped.jpg" which you just saved. You may now browse for the next image you wish to send to PhotoShop to be modified.
Bridge has a couple image modification capabilities, but it's very limited. You can rotate the images, and save copies of selected images elsewhere on your hard drive using the "Export to Hard Drive" function. With PhotoShop being so much better suited for these functions, I see little need for ever using "Export to Hard Drive" in Bridge.

Summary... browse with Bridge - make changes and save them with PhotoShop - browse with Bridge.
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Old 11-02-2010, 07:39 PM   #7
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About "Image Size"...

Refer to the first attachment. It's the image I cropped at 4X6 inches with a resolution of 300dpi. As you can see, the pixel dimensions are 4*300=1200 height and 6*300=1800 width. I can only do two things here... make it bigger or make it smaller. If you change the size in the Pixel Dimension area, CS5 will automatically change the Document Size (which is simply the size of the hard copy print you will get). Likewise, if you change it in the Document Size area, CS5 will adjust the pixel dimensions.

If I make it smaller, pixels will be discarded. As you can see in the second attachment, I specified to make it half the size by changing Document Size. CS5 changed the pixel dimensions to 900x600 pixels.

If I make it larger, pixels will be added. In the third attachment, I changed Document Size to 8x12... twice the height and twice the width. CS5 changed the pixel dimensions to 3600x2400. It's worth noting here, that the original image is 1200*1800=2,160,000 pixels in size (2 megapixels). After it is upsized, it becomes 3600*2400=8,640,00 pixels (8.6 megapixels). CS5 must ADD 6,480,000 pixels to this image, and guess what color to paint each one of them.

That's where resampling comes in. CS5 uses the colors of adjacent pixels to decide what color the added pixels should be. There are 5 different algorithms to choose from. CS5 indicates you should use Bicubic Smoother for enlargements and Bicubic Sharper for reductions, but for exersize, you can resize the image 5 times, using each one of the resampling algorithms, compare them afterward, and keep the one you like best. You can do a 6th one by turning Resample Image OFF.

Scale Styles in your case probably makes no difference if it's checked or not checked. If your image has layers with styles applied to them, select Scale Styles to scale the effects in the resized image. I doubt this applies to you.

You always want to check Constrain Proportions, to maintain the current ratio of pixel width to pixel height. This option automatically updates the width as you change the height, and vice versa. This proportion is also referred to as aspect ratio. In the example of a 4x6 image, the aspect ratio is 2:3, that is, for every 2 units tall it is, it 3 units wide. Imagine what your picture would look like if you make it wider, but not taller.
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Old 11-02-2010, 08:42 PM   #8
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Quote:
Originally Posted by Shoalwater17 View Post
I have about drove myself crazy trying to figure this out. I'm using Photoshop Cs5 and as any photographer knows you have to crop photographs at times for the desired effect. Let's see if I can explain this. If I want to crop a photo but keep the original pixel dimensions, can this be done? What I'm finding is when I crop (in PS or Camera Raw) the pixel size is reduced as well as the file size. I know the file size will be reduced and I don't care. The problem I see when cropping is when cropped, the file can reduce to something like "1200 x 800 ppi". This is fine for computer viewing but what if you are trying to submit to a stock photo site? They have minimums for uploads and cropped images are often less than these minimums, usually 1600 x 1200 and/or 2MP. It's always (I think) better to upload a photo close to it's original size if possible. I hope this makes sense.

Thanks in advance.
Cropping does not resample and upsize or downsize unless you have pixel dimensions specified in the little boxes on the toolbar line for the crop tool. But, don't do it that way because you cannot specify how it's done there, only the size. Instead, crop with the pixel dimensions left blank so that you are actually cropping to pixel size. Then, go into edit image-size and set the end result size you want there. Notice in image size there's a pop open dialog menu with different ways that you can do the resizing. Pick whatever is best for whether you are enlarging, or reducing. Note there are two options for reducing size, try both and you'll see which looks best to your eyes. Nearest Edge maintains sharpness of hard edges best, but is not good for "busy" scenes like foilage. If there's a lot of sky like at sunset, use maintain gradient to avoid color banding. When you resize at the same time you crop, you cannot select which method is used for the resampling needed to re-size.
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Old 11-02-2010, 09:14 PM   #9
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Quote:
Originally Posted by Pocketfisherman View Post
Cropping does not resample and upsize or downsize unless you have pixel dimensions specified in the little boxes on the toolbar line for the crop tool.
Good points all, Pocketfisherman.

The only thing I might add just to avoid confusion, is that cropping can never "upsize". Cropping will ALWAYS downsize, either to the dimension of the crop frame, or to the dimension specified on the toolbar line.
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Old 11-03-2010, 08:14 AM   #10
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Just tried it in CS5, and it did upsize with no problem in the crop tool. You can upsize crop to pixel dimension larger than the original by putting the numbers in the crop dimension boxes. It violates the definition of "crop", but it does work.
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