Image resizing issues

[Janissary]

Hi, I have a bunch of approximately 1600X1200 jpeg images of my models. These typically come from my C_a_n_o_n A620 camera. I process them in iPhoto to crop, adjust lighting etc. The result is approximately 1600X1200 jpeg images. I save them, and I am generally happy with the results.

Here is one example (1600X1123)

I need this size for viewing the pics on my computer in the full screen mode etc.

When posting to forums such as this one, I typically try to keep my images to max size to 1024. So, I export all these images in iPhoto in a new size with the max dimension set at 1024. This resizing introduces a blur that just annoys me. Here is an example of the resized image (1024X719):

The results might be easier to view by downloading both images and comparing them in an image viewer with both images at the same physical size.

It may be subtle, but the blur is there. My question is, whether this blur is avoidable. I recognize that any sizing (even if downsizing) will introduce some loss especially with jpegs. But I wanted to know if I could achieve better results than this. Some pieces of information:

- I currently don't have the Raw format capability with my camera. With some firmware update and hacking this seems possible, but I am hoping to address this issue without the Raw format route.

- I tried this resizing in iPhoto and Picasa with similar (disappointing) results. I used to have IrfanView on my Windows machine, and I remember being very satisfied with the outcomes. Even though I have bootcamp on my mac (ie, a windows partition for mac), I would prefer not to switch to windows each time I need to do this.

- For iPhoto users: I resize an image by File > Export > Size: Custom: max dim: 1024 > Jpeg quality: Medium. I tried setting the Jpeg quality as High and Maximum, but get similar poor results at the expense of bigger file sizes.

- I don't want to take my original pictures at 1024 (even though that would eliminate the need for resizing) because I need the bigger images for non-web-based viewing and sharing as I mentioned.

If there is more information I can provide about my objectives and tools, let me know. I am really hoping to resolve this issue. This blur maybe something unavoidable, but I still wanted to get the experts' opinion on this. Thanks for your help in advance!

Edited June 10, 2013 by Janissary

[RichardL]

You need to resize in a factor of 2 in order to avoid getting blurry images. For example, if your original size is 1600X1200, then scaling it down to 800x600 would give the sharpest image. Then bring the scaled down image into a high end photo editing software like Photoshop and use the "unsharp mask" image filter.

[RichardL]

Correction, you need to resize your original image by a "power of 2" for best results. In other words, make sure both the width and height are divisible by a power of 2.

[Lodewijk]

Whenever you resize raster images there will be a loss of quality. It can be minimized, but it is unavoidable.

[Janissary]

Thank you guys. I wish the power of 2 method was an option, unfortunately cropping the pics causes arbitrary changes to the height/width. I guess I could refine it by adjusting my cropping mask, but that too would rarely guarantee I am at a proper height and width. The thing is I was much happier when I had IrfanView. I just cannot explain where the difference stems from. I read that it might have to do with the interpolation function that gets used, but I don't have a deep knowledge of these different software. I don't have Photoshop.

I could use the sharpening tool to sharpen the image, I will give that a try. My experience though is that it often looks very artificially sharpened (at least in iPhoto).

Another strange thing I observe is that after an editing operation, iPhoto will turn a picture to 72dpi no matter what. There is no way to set it to a custom dpi. In this context, dpi is probably irrelevant because all my needs involve computer viewing (no physical printing). Nonetheless, that peculiarity is something I have found to be bizarre.

[Bob Beary]

In I Photo there should be a check box when resizing photos to "constrain" the sizing. That way the reduced photo will be "constrained" or limited to the same proportions as the original.

HTH

Bob

[peebeep]

Does iphoto re-size or re-sample the image? If it's re-sampling then the amount of pixels is reduced, which degrades the image quality. If it's re-sizing, then the image should still contain the same amount of pixels, so for best image quality re-sizing is preferred. Re-sizing or re-sampling dialogue boxes should contain a tick box that says 'maintain aspect ratio' or something similar. If this box is checked you can change one of the image dimensions and the other one will be altered proportionally.

peebeep

[huntermountain]

I use BDsizer, a free batch resizer. There's a choice of three resizing methods, and the option to sharpen the resized images( and add a frame or watermark). Maybe you could experiment with it to see if you get more satisfying results.

BDSIZER

Edited to change the link to something that doesn't require you to use their 'download manager')

Edited June 11, 2013 by huntermountain

[RichardL]

I could use the sharpening tool to sharpen the image, I will give that a try. My experience though is that it often looks very artificially sharpened (at least in iPhoto).

You don't want to use just any sharpening tool. You want to use "Unsharp Mask" or USM. Might want to do some reading about this filter. Adobe Elements has it, and Elements is much more affordable than Photoshop. Version 11 can be had for under $65.

[Janissary]

Thanks for the input everybody. iPhoto does have a dialog box to set the new size of the image during export. So this is where I change the size of the image. I don't have much of a difficulty preserving the aspect ratio; I set the max dimension of the image to be whatever (1000pixels below), and it takes care of the other dimension. Perhaps I need to make sure that whatever the starting dimensions are, say (1583X714), the new dimensions should be integer values also.

So, in the example I gave, 1583 tries to become 1000 pixels, and the other dimension thusly tries to become 714X1000/1583 = 451.04 pixels. This rounds probably to 451. So these might contribute to the problem.

Just to summarize my steps:

- Shoot the scene with my A620 powershot

- Save the image to my computer in JPG, 1600X1200.

- Edit this image in iPhoto including lighting.

-Crop the image in iPhoto. This is where I create the cropping region manually and it depends on how the model is situated with respect to the image frame etc. So, here this might produce a 1583X714 image like I exemplified above. It is difficult for me to set the cropping mask to be multiples or powers of 2.

- Save this resulting 1583X714 image as my original image. No problems with this image. It looks nice.

- Export this image using the dialog box above to create a smaller version of it (max dimension 1000 pixels) to publish on the web.

- This new version at times is blurry.

I appreciate the help thus far. I guess I will use what you guys mentioned to read more on this. Thanks you once again.

[KursadA]

I hardly ever use any of the GUI tools for resizing or resampling unless I need to do some cropping, and in many cases I would do cropping after the resizing. I depend heavily on the command line tools provided by ImageMagick. I just happen to know that you're very comfortable with programming and using the command line, so why don't you take a look at ImageMagick - it's free and available for OS X as well. ImageMagick's resizing/conversion utility ("convert") has a truly mind-boggling array of adjustable parameters and customizability beyond any commercial tool out there. I have no doubt you can do any kind of image resizing with it, and can use the same script to do it on multiple images very easily afterwards.

FYI: The Caracal Models decal design flow heavily relies on programmability and file conversion capabilities of ImageMagick, GIMP and several other command-line Linux/ Unix utilities. It is the higher degree of automation and batch processing that allows me to work very fast and efficiently.

Edited June 13, 2013 by KursadA

[Janissary]

Thank you very much Kursad. This looks very promising. I will have to study it in greater depth but it looks quite comprehensive.

[geedubelyer]

Hi Jannisary.

Would "Easy Thumbs" by Fookes be of any use to you?

I've used it regularly since John Wolstenholme suggested it and it works beautifully. Almost every image I post on the web is reduced to about 100kb but they still look respectable on my monitor (the resolution, not necessarily the content )

HTH