Resizing without jagged edges ? (1 Viewer)

widdywiddyuk · Jun 21, 2006

Perhaps one of the image experts out there can answer this.

I have some images which when resampled (to make them small enough dimensions for the database) result in the edges being jagged.

How do I avoid this ? Some sort of filter, or some other method ?
For quickness I use IRFANview. Photoshop & Paint Shop Pro also
options.

Any advice on this common problem welcomed.

Cheers,

Woody

BenBirding · Jun 21, 2006

You need a program that uses high quality scaling. I recommend this program:
http://www.snapfiles.com/get/pixresizer.html
It's free and does its job quite quickly and efficiently.

saluki · Jun 21, 2006

widdywiddyuk said:
Perhaps one of the image experts out there can answer this.

I have some images which when resampled (to make them small enough dimensions for the database) result in the edges being jagged.

How do I avoid this ? Some sort of filter, or some other method ?
For quickness I use IRFANview. Photoshop & Paint Shop Pro also
options.

Any advice on this common problem welcomed.

Cheers,

Woody

In Photoshop go to File/Save for Web.Top left click on 4-up tab, click on 2nd pic. Bottom right click on Image Size and set to 800 width. Change quality setting so that pic is under 200k (file size is in bottom left of image). Click 'Save' and rename to different than original if that is .jpg. No need for any other software.

saluki

bpw · Jun 21, 2006

I wonder what you mean by jagged edges? Do they have this in Photoshop or when displayed in a browser?

I agree with Saluki, if you have Photoshop you have what you need. My method (there are many) in Photoshop is:

File > Automate > Fit Image: Enter the max size you want in either direction (height or width) for the image in both boxes (e.g. 600 pixels).

File > Save for Web: JPEG, High quality (can play around with quality here to influence file size if important). If you want to set a target size from here, select the ‘Optimize Menu’ (little arrow top right in Photoshop CS), select: ‘Optimize To File Size’ and enter the ‘Desired File Size’, e.g. 60k.

Save with different name or to a different folder.

If you work to similar dimensions with all your images, you can run these as an action in Photoshop– one click.

delia todd · Jun 21, 2006

bpw said:
in Photoshop is:

Image > Image Size > Resolution: set to 96 pixels/inch

I just change the longest dimension from whatever to 800 - that's in the box that's already highlighted.

bpw said:
If you work to similar dimensions with all your images, you can run these as an action in Photoshop– one click.

ooh how do you do that?

Look like you've lots of choices Woody

D

bpw · Jun 21, 2006

delia todd said:
I just change the longest dimension from whatever to 800 - that's in the box that's already highlighted.

Are you doing this in the 'Image Size' dialogue? If so, do you change the resolution?

delia todd · Jun 21, 2006

bpw said:
Are you doing this in the 'Image Size' dialogue? If so, do you change the resolution?

Hi BPW, yes it's in Image Size' and no, I don't change anything else - easy peasy o

well it needs to be for me.:gh:

D

bpw · Jun 22, 2006

delia todd said:
Hi BPW, yes it's in Image Size' and no, I don't change anything else - easy peasy o well it needs to be for me.:gh

After resizing do you use ‘Save for Web?

I use ‘File > Automate > Fit Image’ so I can use it in an ‘Action’ when preparing images for the Web. Typing the same values in both boxes will result in an image that is no higher or wider than these values, regardless of whether it is portrait or landscape image; it can therefore be automated. This is only of use to you of course if you produce images of similar dimensions every time, e.g. 600 x 400 or 400 x 600.

delia todd · Jun 22, 2006

bpw said:
After resizing do you use ‘Save for Web?

I use ‘File > Automate > Fit Image’ so I can use it in an ‘Action’ when preparing images for the Web. Typing the same values in both boxes will result in an image that is no higher or wider than these values, regardless of whether it is portrait or landscape image; it can therefore be automated. This is only of use to you of course if you produce images of similar dimensions every time, e.g. 600 x 400 or 400 x 600.

Hi Paul

No I don't.

Here is my exact route for this recent picture, done in Photoshop.

Image>Resize>Image Size

The picture started at width 2272, height 1704

I changed the width to 800 and the height automatically changes. OK that

I then Save As: changing the name to whatever.

I simply OK the next box, which is JPEG options (it was left on "Quality 6, Medium".

Voila - done.

D

widdywiddyuk · Jun 22, 2006

Thanks for all the help here. I tried a few of the techniques out and it still appeared jaggy. HOWEVER ... on poking around and trying some things it seems that it was the way the image was being displayed by the various pieces of software. It was optimising the size for some reason .... showing the image as 100% actual size showed it just fine. SO.... another pic about to go into the photo gallery under invertebrates/insects.

Cheers,

Woody

bpw · Jun 22, 2006

delia todd said:
Hi Paul

No I don't.

Here is my exact route for this recent picture, done in Photoshop.

Image>Resize>Image Size

The picture started at width 2272, height 1704

I changed the width to 800 and the height automatically changes. OK that

I then Save As: changing the name to whatever.

I simply OK the next box, which is JPEG options (it was left on "Quality 6, Medium".

Voila - done.

D

Ok, but if the image is purely for web display, you should ideally change the resolution to match PC monitors (most 72ppi some 96ppi). This can reduce the file size considerably depending on the existing resolution. Also, if the resolution is high enough, the image might be downloaded and produce an acceptable print. A resolution of 72ppi will not produce a good print.

Save for Web changes the resolution to 72ppi, or you can do it manually in the Image Size dialogue.

I actually suspect that your images may already be at 72ppi perhaps?

delia todd · Jun 22, 2006

bpw said:
Ok, but if the image is purely for web display, you should ideally change the resolution to match PC monitors (most 72ppi some 96ppi). This can reduce the file size considerably depending on the existing resolution. Also, if the resolution is high enough, the image might be downloaded and produce an acceptable print. A resolution of 72ppi will not produce a good print.

Save for Web changes the resolution to 72ppi, or you can do it manually in the Image Size dialogue.

I actually suspect that your images may already be at 72ppi perhaps?

Well I had to go and look, 'cos I hadn't a clue what you were talking about :eek!: and yes, they are 72ppi. Nothing I've done has given this resolution though - I wouldn't have known why, how or when to change it.

I'm not really sure what point you are trying to make now though, virtually all my pictures* are downloaded to threads and occasionally into the gallery and what I do seems to work hassle-free.

*erm.... what I mean is pictures I want to down-load, not ALL my pictures

D

bpw · Jun 22, 2006

delia todd said:
I'm not really sure what point you are trying to make now though, virtually all my pictures* are downloaded to threads and occasionally into the gallery and what I do seems to work hassle-free.

What you are doing Delia is spot on for Web display. Your images are already at 72ppi so simply resizing them is fine. I was assuming that the resolution of your images would be higher; perhaps they come off the camera at 72ppi?

For most (and perhaps for Woody who started this thread), the image resolution is much higher when it comes off the camera. This is when it is a good idea to reduce the resolution to between 72 to 96ppi for the reasons stated above.

Hope you weren’t hanging over the cliff to get that shot!

Recurvirostra · Jun 22, 2006

It doesn't really matter if the image is set at 72ppi, 96ppi, or any other value when viewing on a monitor. If the image is, say, set to be 800 pixels wide, then that's what it will be - 800 pixels wide on whatever monitor you are viewing it on.

The 72ppi (or whatever other value that is set) only has a bearing on the size that the image will be printed at. Then an image would print out approximately 11.1 inches wide (800 ÷ 72). If it was set to 96ppi it would print out roughly 8.3 inches wide (800 ÷ 96) and so on.

delia todd · Jun 22, 2006

bpw said:
What you are doing Delia is spot on for Web display. Your images are already at 72ppi so simply resizing them is fine. I was assuming that the resolution of your images would be higher; perhaps they come off the camera at 72ppi?

For most (and perhaps for Woody who started this thread), the image resolution is much higher when it comes off the camera. This is when it is a good idea to reduce the resolution to between 72 to 96ppi for the reasons stated above.

Hope you weren’t hanging over the cliff to get that shot!

The must do Paul, but I can't find anywhere in the manual about changing it (Coolpix 4500)

Me! Hang over a cliff - no way! :eek!: Just lucky they were up near the path. Mum was shouting at some other people.

D

RAH · Jun 22, 2006

From what I've read and from experience, the ppi setting of an image is not important AT ALL. PPI is a PRINT setting (controls how large it will print). It has nothing to do with the resolution. In other words, if you have an image that is say 800 x 600 and has a ppi of 72, and you change its ppi to say 96, or 200, or 8000, WITHOUT resampling, the result is NO CHANGE to the image, except in how large it will PRINT.

So all this advice about changing the ppi for someone trying to change an image's dimensions (width x height) seems kind of meaningless to me. If you want an image to be reduced in size from 2274 x 1704, to 800 x whatever, use resize/resample, make sure resample is checked, put 800 in the width, let the height adjust automatically, and do it. Has nothing to do with ppi.

As far as I know, most (all?) digital cameras produce images that are 72 dpi directly out of the camera. As I said, this is only important when you are PRINTING the image. When you want to print at a smaller size, you increase the ppi (WITHOUT resampling) and you get progressively smaller prints as you increase the ppi. Just like going to a photo store with film negatives and saying you want 4x6 prints or 5x7 prints. The size of the negatives isn't being altered, just the print size.

Also, Woody, you're correct in saying that you shouldn't view an image at over 100% or it WILL look jaggy on the edges.

Recurvirostra · Jun 22, 2006

That's what I thought I said, RAH.

bpw · Jun 22, 2006

Thank you gents, I’ve learned something today...

I find it amazing that most professional photographers and Web processing software, (including Photoshop) still advise a resolution of 72ppi for Web images. Why? Read this article (there are many out there):

http://www.nicholsonprints.com/Articles/dpi.htm

RAH said:
So all this advice about changing the ppi for someone trying to change an image's dimensions (width x height) seems kind of meaningless to me.

This is not what I was actually suggesting, I realise that these are separate issues. I was referring (incorrectly) to the file size.

RAH said:
By the way, as far as I know, most (all?) digital cameras produce images that are 72 dpi directly out of the camera. As I said, this is only important when you are PRINTING the image.

My Nikon Coolpix produced images at a resolution of 300ppi, but as you say, it makes no difference.

I had a recent email conversation with a very well known photographer who advises reducing the resolution and the reason he does so (apart from reducing the file size, which doesn’t work, I’ve now tried it) is to protect his images from download and print? If I understand the above article correctly, this won’t work either? I emailed him again today, and his response was:

“I am not positive that that is correct, but it does not matter. The images that I prepare for the web look great and I try not to get to involved in technical stuff...”

Fair point I suppose (but he is giving out technical advice)!

A complicated subject!

RAH · Jun 22, 2006

I think that this whole subject is complicated by the fact that many image editors have one dialog box which can be used for 2 completely different kinds of resizing:

1) changing the actual dimensions of the image (width vs height in pixels)

2) changing the size the image will print at.

The first type, changing the dimensions, is done via resampling. The 2nd type, the size it prints at, is done by changing the ppi (also called dpi). The confusion comes because of the fact that some editors allow you to have resampling checked, but also allow you to change the ppi, which, yes, will cause the dimensions to change.

For example, if your image is say 1000x800 with a ppi of 200, it will print at 5 x 4 (1000/200; 800/200). But if you have resample checked and change the ppi to say 100, the image dimensions will be resampled and the image will be downsized to 500 x 400 (maintaining the same print size by lowering the size of the image itself). So the user gets the idea that using ppi is the correct way to change the image's dimensions. But in fact, it is mixing apples and oranges.

If you look at Irfanview's system, it is much clearer. The DPI is set in the image's Properties dialog. Changing the value alters the image's printing size, but does not affect its dimensions. Dpi can also be set in the print dialog, which is also appropriate. In the Resize/resample dialog, there is no mention of dpi. All it talks about is width vs height. This is as it should be.

John S, yes, that is what you said. I actually didn't read all the way down to your explanation. After reading several dpi discussions above it, I entered my first posting, because it seemed to me that folks were making it more confusing than it has to be.

citrinella · Jun 23, 2006

delia todd said:
Originally Posted by bpw
If you work to similar dimensions with all your images, you can run these as an action in Photoshop– one click.

ooh how do you do that?

D

I use Elements v.2

Look under File, Batch processing.

Mike.

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