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Resizing problems


digicammad 18 22.0k 40 United Kingdom
9 Sep 2003 3:04PM
I've noticed a number of people talking about resizing problems, but I can't honestly say I have noticed any on my shots.

I use IrfanView resample or, if I also need to edit the image, 'save for web' in Photoshop. Either way I make sure neither the height nor width exceed 500 pixels.

Do these problems only occur if larger images are submitted and have to be resized by the gallery software?

Ian
Carabosse 18 41.6k 270 England
9 Sep 2003 3:31PM
Using 'Save for Web' in PS does lead to a better on-screen result rather than 'Save' or 'Save As'... somebody did explain why a couple of months ago but I can't remember!

I guess if you let the gallery sofware do the resizing it may degrade the image.
Atlas 18 621 United Kingdom
9 Sep 2003 3:49PM
I have noticed some loss of quality when letting this site resize but it only really seems to show up on LCD monitors.

Rob
mad-dogs 19 2.2k England
9 Sep 2003 4:14PM
Save for web automatically sets the resolution to 72 dpi and removes unnecessary data such as the thumbnail image of the icon.

It reduces the file size by throwing away information which saving as a normal jpeg does not.
bigredtim 18 1 Australia
30 Sep 2003 7:59PM
I have noticed my photo quaility is not as sharp when I have reduced my pics from 4.1 megapixels. With my old digital camera which was only 330,000 pixels this does not occur. My new camera has a feature where I can copy photos in a smaller size, I intend trying this for any photos I want to submit here and see if they come out better.
brian1208 18 11.8k 12 United Kingdom
30 Sep 2003 8:15PM
Rob, an interesting observation re: problems only showing on LCD monitors. I am one of those who both has problems reducing size of my images and, sometimes, in seeing defects in the photos of others that no one else seems to see.

I wonder if there is some sort of interference pattern between artefacts in the compressed image and the liquid crystal elements in the screen.

I am beginning to see a certain logic in the different effects on differing images.

Downsizing sharp edged, metallic images is simple and gives little loss of quality.

The most difficult, I find, is in downsizing images with subtle colour variation and soft tonal quality.

Portraits and similar images are my worst problem.

There must be some science behind this - time to put my thinking cap on and do some reading.
collinf 18 1.2k
1 Oct 2003 11:06AM
Brian - I assume that from your post you are using an LCD?

One of the first questions I was asked when purchasing a new monitor was: Do you do a lot of digital imaging work? My reply was (obviously) yes. The answer came back that I should NOT purchase an LCD. I do not remember the exact technical response, but it had something to do with the LCD not being capable of showing an image to its true quality. This was then demonstrated. We put the same picture (a digital image of my car) on a CRT and it looked exactly how it was supposed to. We put it on the LCD at the same time (on a different PC) and had the two sat beside each other. The LCD version looked almost washed out and really bad. I went for a 17" CRT in the end.

Collin
brian1208 18 11.8k 12 United Kingdom
1 Oct 2003 1:00PM
Collin - in the main I am very happy that the LCD is capabable of good photo manipulation. I have carried out the following test:
- set up the photo on screen, print photo, scan photo, colour match on screen against original and got very close agreement, using both eye and colour picker. (I have spent a lot of effort colour matching printer, scanner and screen to achieve this - it doesn't work straight out of the box!).

The only time I think I am having problems is when the downsized image has compression artefacts (as is usually the case) and these, sometimes, seem to interact with the transistor spacing on the LCD screen. Its almost like a moire or interference effect.

I never see this with original images whether compressed or not. It only occurs once an image has been through a heavy downsizing and file compression for web saving.

Even then it is not a continual problem. As I say, I think there may be a specific type of image / compression process that causes this.

I need to do more work to understand this effect.

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