Luminous Landscape Forum
Raw & Post Processing, Printing => Digital Image Processing => Topic started by: Ailan on October 10, 2008, 11:38:07 pm
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Hi,
I will appreciate any light on this.
I have been told and havent been able to verify this on the internet or any book that using the crop tool to straighten and crop an image in Photoshop degrades the quality of it, and its better to use the marquee tool to crop it and the straighten ruler to do the latter.
Is this right?
Many thanks.
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I have been using the crop tool for 10 years and haven't noticed any degradation.
I use the ruler to straighten the horizon first, then crop.
Just seems logical to use the crop tool if you are cropping and the selection tool if you are selecting.
Rich
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A picture is only degraded when cropped if it is in a degradeable format; ie .jpg.
.Psd, .Tif, and .Bmp should not make a difference, because there is no encoded compression.
Michael
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I have been told and havent been able to verify this on the internet or any book that using the crop tool to straighten and crop an image in Photoshop degrades the quality of it, and its better to use the marquee tool to crop it and the straighten ruler to do the latter.
Just to be clear, "cropping" does NOT do anything other than eliminate some pixels...ok? However, when you crop AND rotate, or JUST rotate an image in Photoshop, it requires an interpolation if the rotation is anything other than +-90º or 180º. Rotating requires changing the pixels and whether you do it in a crop or in a rotate after a crop done by marque it doesn't matter. In that regard, it's 6 of one and 1/2 dozen of the other (depending on your "default" resampling preferences which can make a difference, you really only want to use Bicubic for rotation).
So, don't fall prey to that faulty info...
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Just to be clear, "cropping" does NOT to anything other than eliminate some pixels...ok? However, when you crop and rotate, or just rotate and image in Photoshop it required an interpolation if the rotation is anything other than +-90º or 180º. Rotating requires changing the pixels and whether you do it in a crop or a rotate after a crop done by marque. In that regard, it's 6 of one and 1/2 dozen of the other (depending on your "default" resampling preferences which can make a difference, you really only want to use Bicubic for rotation).
So, don't fall prey to that faulty info...
Many thanks Mr. Schewe, and everybody. I appreciate your help a lot.
Everything is clear now, but just to confirm one thing if you would please.
If I use the straighten tool it also interpolates the image, right?
Many thanks again.
best regards,
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If I use the straighten tool it also interpolates the image, right?
Yes. Any rotation other than ±90˚ & 180˚ requires interpolation. The interpolation algorithm used is the one specified in your program prefs.
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Schewe,
With respect, are you saying that Photoshop does not "hurt" a .jpg image when only a crop is performed?
V/R
Michael
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Just to be clear...
Sorry, but there was nothing particularly clear about Mr. Schewe's late evening post. Considering Mr. Schewe is a successful author, readers should not have to endure typing errors and/or a mish-mash of misplaced prepositions, missing verbs and poor sentence structure. Frankly, Mr. Schewe's post on this thread is most confusing and unclear. Maybe he had too much wine when he wrote it.
I hope he'll come back and answer the OP's question more clearly (even if tinged with his infamous sour tone).
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Considering Mr. Schewe is a successful author, readers should not have to endure typing errors and/or a mish-mash of misplaced prepositions, missing verbs and poor sentence structure. Frankly, Mr. Schewe's post on this thread is most confusing and unclear.
Well bud, any successful author also has a real good editor to fix the writing...so sorry it was beyond your comprehension (odd that the OP figured it out though even with the original errors)...so I've taken the liberty to do a slight (and I do mean slight) edit...maybe NOW you'll be able to understand it?
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With respect, are you saying that Photoshop does not "hurt" a .jpg image when only a crop is performed?
If you do a non-destructive crop in Camera Raw a JPEG won't undergo any degradation. But any time you open and resave a JPEG, it has to undergo re-compression and thus it degrades...
(I hope THAT'S clear enough...)
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(odd that the OP figured it out though even with the original errors)
Without truly knowing the OP, that's an assumption. I wouldn't bet the cost of Photoshop on such an assumption.
...so I've taken the liberty to do a slight (and I do mean slight) edit...maybe NOW you'll be able to understand it?
Not just me (I'm not that selfish). Now EVERYONE who reads this thread will be better equipped to understand your helpful post. Thank you for clearing your words up.
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Without truly knowing the OP, that's an assumption. I wouldn't bet the cost of Photoshop on such an assumption.
I found it plain + clear what was originally written, despite the typo. As did the authoutr of following post. So maybe it was you who had too much wine when you read it that night.
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I'm going from memory here, but I switched from the crop tool to the rectangular marquee tool in Photoshop some years ago because the crop tool re-sized my images based on the dimensions of the crop. In other words, if I wanted to crop something to a 4x6 size, the crop tool would re-size the image to the correct number of pixels on each side to make a 4x6. The rectangular marquee tool, on the other hand, allows you to crop to a particular ratio (2x3, for instance), but does not change the number of pixels on a side except to reflect the pixels discarded because they were outside the cropped area. That is the same way the crop tool works in Camera Raw. If there is some way to get the Photoshop crop tool to work like the rectangular marquee tool in this regard, I would prefer to use the crop tool, as it gives you more control.
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... and its better to use the marquee tool to crop it and the straighten ruler to do the latter.
BTW, how does one use the "straighten" ruler? I have seen this in Elements, but not in CS3.
Michael
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BTW, how does one use the "straighten" ruler?
It's the ruler and it's part of the eyedropper tool. When the ruler tool is active, you simply click & drag along a line you want to be exactly vertical or horizontal. Go to Image>Rotate>Arbitrary and the degree of rotation is automatically entered (down to the 0.01˚).
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It's the ruler and it's part of the eyedropper tool. When the ruler tool is active, you simply click & drag along a line you want to be exactly vertical or horizontal. Go to Image>Rotate>Arbitrary and the degree of rotation is automatically entered (down to the 0.01˚).
Chris: I have not found the ruler tool, and it would be quite helpful to me. Can you help? I do seascape photography, and almost always have crooked horizons (in spite of having a grid screen on my DSLR), which I usually use rotate canvas command to fix. Thanks for the help.
Dave G in NJ
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Some Photoshop tools have multiple functions and switching through them is easy. Depending on your program prefs you switch through the various tools using the keyboard. To get the eyedropper I tap the "i" key. Another tap gives me the color sampler tool and another tap on the "i" key brings up the measure tool. This way of accessing the different tools is fundamental to Photoshop use. Check it out in the manual.
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I'm going from memory here, but I switched from the crop tool to the rectangular marquee tool in Photoshop some years ago because the crop tool re-sized my images based on the dimensions of the crop. In other words, if I wanted to crop something to a 4x6 size, the crop tool would re-size the image to the correct number of pixels on each side to make a 4x6. The rectangular marquee tool, on the other hand, allows you to crop to a particular ratio (2x3, for instance), but does not change the number of pixels on a side except to reflect the pixels discarded because they were outside the cropped area. That is the same way the crop tool works in Camera Raw. If there is some way to get the Photoshop crop tool to work like the rectangular marquee tool in this regard, I would prefer to use the crop tool, as it gives you more control.
Chris, I think that if you use the crop tool in photoshop and leave the resolution box empty, the crop is simply made at the proportions in the other two boxes.
So if you put in 6 by 4, it does not matter if the units are inches, centimetres or elephants. The crop tool will not resample the pixels. Just crop the picture to
the ratio of 6 by 4.
Jim
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Some Photoshop tools have multiple functions and switching through them is easy. Depending on your program prefs you switch through the various tools using the keyboard. To get the eyedropper I tap the "i" key. Another tap gives me the color sampler tool and another tap on the "i" key brings up the measure tool. This way of accessing the different tools is fundamental to Photoshop use. Check it out in the manual.
Thanks Chris. I'll give it a try.
Dave
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Not so - it resamples to some very odd dpi figures if you try - very aggravating when backward progress is built in like this - I'm not the only one who wants the old "aspect ratio crop" then - Adobe are you listening ?
Thanks Chris. I'll give it a try.
Dave
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Not so - it resamples to some very odd dpi figures if you try - very aggravating when backward progress is built in like this - I'm not the only one who wants the old "aspect ratio crop" then - Adobe are you listening ?
I actually find myself cropping in Photoshop less, doing it in Lightroom. But there are still occasions where I might need to crop in Photoshop.
If the Resolution box is empty, it doesn't resample, it assigns those dimensions to the image, then makes a corresponding adjustment to the DPI. This is the same thing as using image size with the resample box turned off. You can also indicate a final resolution, and leave the width and Height box empty, you will then get the DPI you have specified and the corresponding calculated height and width.
Only if you provide all three numbers will Photoshop actually re-sample the image to the specified numbers.
I agree, it would be nice to simply indicate a proportion in the crop tool box, much like Lightroom. But you can use the tool to crop to do aspect ratio cropping without the image being re-sampled, and then if necessary modify the image size settings without resampling to achieve a more appropriate range.
I personally prefer the crop tool because it is easier to modify to achieve your final crop. I normally put what I think my target final size is for the image. Often I only put one number in ... the longest side. This will then calculate all other numbers, and provides me a useful DPI number ... if the number is too low I either don't print that large, or occasionally will try a 200% uprez. I have been very pleased with the concept taught by Jeff Schewe regarding not interpolating to output size, but letting the printer driver handle it as long as the DPI falls within an acceptable range.