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Cropping and Image Qaulity


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puppychew

Power User
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Hello,
I need to crop photos for web use. They need to be 300x400 px for the web page they will go on.

I thought I was doing good until I watched a tutorial on Lynda.com that said I may be stretching out the image and reducing quality - it ended there with no explanation.

So this is what I have been doing.

a photo 1200x1600 photoshop size 5.4M, camera photo size is about 1000K, apx. 6x8 inches, resolution 180 - this is from the image size menu which I do not change.

I make my color adjustments etc in photoshop, save as a photoshop file, then crop it.

I do not use the image size menu - I didn't think I needed to.

To crop, i set the crop to 300x400 and outline the part I need to show on the web.

If I were to check the Image Size box, it is 300x400 and 1.6x2 inches

I then save to web. The JPEG size on high quality is about 20K.

My confusion:
Is my process above correct?

Sometimes the object I need to focus on requires more cropping - meaning I am cutting out a smaller part of the photo to fit the 300x400. Am I stretching pixels of this small cropped part and decreasing quality?

Quality and being able to see detail is important.

I appreciate help in this - still learning.
thanks in advance!
 
If you want to use only a section of the image, you have no choice but to crop it. Doing so it not stretching pixels, you are simply using less of them.
 
so I am only using the pixels I have selected in the crop. If the size of the crop 300x400 is larger than the selection to crop, there will be less pixels. Then will there not be a decrease in quality?
 
It might have an effect. You are working with a 180 ppi resolution image. If you use the save to web option, PS will save it at the web's 72 ppi.

Then again the effect may not be noticeable unless you zoom in REAL close......
 
When you crop, you are essentially throwing away the unused portion (pixels). The quality hasn't changed but the picture is now smaller (contains less pixels) so if you tried to make it the same physical dimensions as the original, it wouldn't look as good.

Look at the data under image size for the original. Now crop and look at the data again. The resolution will be the same, but the pixel dimensions will be less.

For this picture I cropped out a section (red outline) and pasted onto the original, as you can see there is no difference in quality.
 
Thanks so I'm doing ok. That Lynda.com tutorial got me confused. I was thinking that I should reduce or increase the size of the image or adjust canvas size before cropping.
 
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