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Post by BuckSkin on May 16, 2015 1:22:39 GMT
I wasn't sure where this question fit, so I put it here.
I hope I can word this well enough so as to get my point across.
It is my understanding that a digital image file has a specific number of pixels, X-many pixels across by X-many pixels high.
It is also my understanding that each particular one of those pixels contains a certain part of the image, whether it is a portion of a blade of grass or a portion of a cow's eyelash.
Using large/fine images from my particular DSLR as an example, when one of my images is loaded in the editor, it displays as 60-inches wide by 40-inches high at 72-PPI. (this is always how they display even though I have changed to 96-PPI in preferences.)
If I choose the Crop tool and select "use photo ratio", regardless of how much or how little of the image I discard, the resulting cropped image will be the same 40x60 dimensions as the original full-size image and still 72-PPI.
How can this even be possible ? ; this flies in the face of everything I know about math and pixels; I have just cut away portions of my original image and yet the new cropped image contains exactly the same amount of pixels as the original un-cut image.
Considering the above, the resultant cropped image appears to lose detail, in much the same way that the lettering on a balloon loses detail when it is over-inflated.
I believe a better option would be a choice to constrain proportions, such that the cropped image will still be the original 2:3 ratio, just smaller in dimensions.
Am I correct in my observations that a "use photo ratio" cropped image suffers a loss of detail ?
I much prefer to keep my images at their original 2:3 ratio, as I like to make slide-show movie DVDs and they just display better on the TV screen when every one of them is the same ratio.
I have used the custom setting, entering a width and height measurement and then lining my crop with the appropriate marks on the grid, thus achieving my goal without losing detail; however, this method forces me to do the math and enter the correct coordinates every time.
Thanks for reading. 
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Deleted
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Post by Deleted on May 16, 2015 6:03:33 GMT
Hi BuckSkin,
First of all, PPI is meaningless when viewing images on a screen. PPI is used to set a print size when submitting your image to print.
For example, say you have a 3600px x 2400px image and you want a 6"x 4" print. Then you would set the ppi to 600ppi. Note, your image would still be 3600px a 2400px in size. As a rough rule of thumb, 300ppi is needed on an image to get a good quality print, assuming the image quality is good (not blurred etc) in the first place. So if you divide the number of your X and Y pixels by 300 you'll get the size of the largest print (in inches) you can make.
Getting back to your issue.
If you use "use photo ratio" in the crop tool you will notice that the values of the Width, Height and Resolution in the parameters bar are set to whatever they are for the current image in your editor and those will be the dimensions of your crop.
So if your original image is, say, 3000px x 2000px and your crop dimensions are 100px x 100px, then your 100px x 100px pixel data will be extrapolated out to the original 3000px x 2000px which means a huge loss of image quality, especially if making a large print.
To make a 100% crop (crop actual pixels without changing their data or changing image quality), which I think is what you are alluding to, I find this the easiest process:
1) Say my original image is 5081px x 2674px (240ppi in the editor) and I want to make an A4 print.
2) Select the Crop tool with "No Restriction"
3) Set W = 297mm and H = 210mm and Resolution LEAVE BLANK. Do not enter a value for Resolution.
4) I then make a crop selection to whatever I feel look nice for a print. The crop bounding box will have an A4 aspect ratio because of the setting in 3)
5) If your crop dimensions turn out to be 3694px x 2612px, for example, you will notice that the images ppi (in the bottom left hand corner) has been reset to 315ppi to match the dimensions of an A4 sheet.
As long as my PPI is greater than ~280 ppi, then I am happy to make a print.
For cropping images to display on a TV, instead of W = 297mm and H = 210mm in 3) you could W = 1920px and H = 1080px or whatever suits. The rest of the process is the same.
Just make sure the number of X and Y pixels in your images is the same or larger than the number of X and Y pixels in the largest screen (TV or whatever) your images will be displayed on.
Remember, PPI is meaningless when viewing images on any type of screen.. The number of X and Y pixels AND the quality of their RGB values determine how your image will appear on a screen.
Hope this helps
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craftysnapper
Junior Forum Member
Posts: 184 
Open to constructive criticism of photos: Yes
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Post by craftysnapper on May 16, 2015 7:34:57 GMT
I am not fan of this feature at all unless absolutely necessary,what it is doing is interpolating pixels ,guessing and making pixels up from the surrounding ones to keep the image size the same with the resultant drop in quality.
If you want to crop to ratio then set that and make your crop then before actually commiting cropping change it to no restriction you crop will remain the same but with out the interpolation.
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Deleted
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Post by Deleted on May 16, 2015 8:05:03 GMT
..................,what it is doing is interpolating pixels,.........................
No, it's actually extrapolating. Not interpolating because it is "guesstimating" pixel data beyond the cropped dimensions back to the image's original, larger dimensions.
I'm splitting hairs here but for the sake of correctness, the differenxce between interpolation and extrapolation needs to be understood.
Difference between Extrapolation and Interpolation
The rest of what you said I agree with because it's essentially what I posted, but summarised.
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Deleted
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Post by Deleted on May 16, 2015 8:34:41 GMT
This is symptomatic of the crop tool which has the option to resample the image depending on what options you choose. Therefore I prefer to use the Rectangular Marquee Tool to define the area to be cropped and then follow this with Image > Crop. This doesn't perform any resampling but should you find you need some then you can do this with Image > Resize which brings the amount under your control. BTW: It's 'Interpolating' No pixels are added outside of the cropped area, instead additional pixels are fitted in between those pixels left immediately after the crop. If it was extrapolated then pixels would only be added outside the cropped area and PS can't guess from that what they should be since within the cropped area there may well be random variations of tones and brightness. Colin |
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Deleted
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Post by Deleted on May 16, 2015 9:01:14 GMT
.................BTW: It's 'Interpolating' ......... Colin
Yes you're right....I was thinking of something else 
I used to crop using the Marquee Tool and Image->crop but then accidentally stumbled across using the crop tool directly when I was playing with its Resolution value. I found that if Resolution is left blank, as posted earlier, then the crop tool does not resample. If you do enter a value for Resolution, then it does.
Leaving the Resolution value blank in the crop tool allows you to do a 100% crop with the flexibility of specifying cropped dimensions in px, mm or inches all in 1 step thus avoiding the extra step of Image->Crop if using the Rectangular Marquee Tool.
I think I'll butt out from this thread from here on
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Post by cats4jan on May 17, 2015 2:43:20 GMT
I am not a fan of cropping. I use the marquee tool to make a selection of my original and use
control/command j to place this selection on a new layer. When you turn off your original layer, you have your cropped image.
This method allows me to make several "crops" without a lot of difficulty.
If I need a specific size, I use the grid.
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craftysnapper
Junior Forum Member
Posts: 184
Open to constructive criticism of photos: Yes
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Post by craftysnapper on May 17, 2015 6:55:41 GMT
.................BTW: It's 'Interpolating' ......... Colin
Yes you're right....I was thinking of something else
And there was I thinking I was the one who was originally right.  |
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Post by BuckSkin on May 17, 2015 15:41:29 GMT
If you want to crop to ratio then set that and make your crop then before actually commiting cropping change it to no restriction you crop will remain the same but with out the interpolation.
THIS ^^^ is what I was looking for; THANKS !!!
I just experimented with this method and it does just what I was aiming for; I did not know that the crop options could be changed once the crop had been described/drawn/highlighted on the image.
This method does in about half-a-second what I had been taking forever to accomplish following my method of doing the math and then using a magnifying glass while counting those tiny grid lines.
I also wish to express my appreciation to everyone who has provided their information and solutions; I have read and re-read every single post and intend to study and practice them more; I have learned a lot.
Using the marquee tool to define a crop should prove handy in various situations, especially when making odd sized crops.
davep9 has given me something else to learn about, as I have no idea what an "A4" print is and figure maybe I should know.
Please keep the ideas coming.
Thanks.
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Post by BuckSkin on May 17, 2015 15:48:55 GMT
Considering this ^^^ method, one could have more than one "crop" layer in a layered PSD file and turn visibility ON/OFF to compare the results.
Thanks.
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Deleted
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Post by Deleted on May 17, 2015 21:54:11 GMT
Hi BuckSkin,
Glad to see you got a solution and useful extra information from everyone.
A4 is one of the international A series paper sizes. I'm guessing you're from the US or Canada because in the link below you will see
"..... The A series of paper is the most commonly used worldwide, with only the US and Canada not currently conforming to the ISO standard. ......"
Anyway, if you are interested you can find more information on paper sizes (photo, print etc) at Everything You Need To Know About Paper Sizes.
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Post by BuckSkin on May 18, 2015 4:11:21 GMT
Hi BuckSkin,
Glad to see you got a solution and useful extra information from everyone.
A4 is one of the international A series paper sizes. I'm guessing you're from the US or Canada because in the link below you will see
"..... The A series of paper is the most commonly used worldwide, with only the US and Canada not currently conforming to the ISO standard. ......"
Anyway, if you are interested you can find more information on paper sizes (photo, print etc) at Everything You Need To Know About Paper Sizes.
Thanks for the link; I will for sure give it a good reading.
Before our recent introduction into the world of photography, I had never really given "standard" print and frame sizes much consideration; if you were on a budget, you had your film developed into 4x6 prints (which is the only common size that matches the 2:3 ratio of a 35mm image); if you could afford the extra expense, you got 5x7s; and, if you wanted to give grandma a nice big framed picture, it was an 8x10.
For at least the last fifty years, in America, 2:3 ratio 35mm format has been king.
Curiously, with the exception of small 4x6, none of the commonly available "standard" frame or print sizes are 2:3 ratio, requiring one to sacrifice image detail in order for the image to conform to the print or frame.
Now that I know more about such things, it bewilders me as to why "standard" frame and print sizes conflict so with the most common 2:3 image format.
Other than economy of materials, is there a logical reason for this that I am missing ?
Thanks.
On another note: Am I the only one that has difficulty making replies to posts; I put my cursor right where I think it should be and the next thing I know I am typing in the middle of someone else's sentence..... 
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