An Experiment with Image Sizes

[Johnwnjr]

An Experiment with Image Sizes

In Photoshop Elements it is possible to select two slides and view them on the screen at the same time. I therefore scanned in a photograph from a film slide, finishing up with a JPEG image at 2224 x 1467. Then giving it a different name reduced it in Photoshop Elements to 1024 x 768. So with apparently two identical pictures, I examined them one above the other. I didn’t expect to see any difference because the computer screen is set for 1024 x 768, but I did:-

They first appear at different sizes, but even then the larger image had better quality.

I magnified the larger image by 100% for detail and to bring the smaller one up to the same viewing size had to magnify it 200%. As these are now viewed at the same size image on the screen it was easier to see that the larger image had the best quality. The smaller image has about half the number of pixels as the larger one, that is the reason the magnification has to be as stated.

According to Lin Evans (professional photographer) who has used all the programs mentioned “PicturesToExe allows full resolution images and ProShow Gold and ProShow Producer do not. Rather than allow full resolution images they optimize for DVD quality (low resolution) then interpolate upward from not more than 800 x 600 pixels to effect executable slideshows with greater screen display resolutions. This takes a serious toll on image quality which is in part why so many professional photographers prefer PicturesToExe.”

The reason for reducing to 1024 x 768 pixels has been to have smaller files for the computers to handle and is the limit most reasonably priced projectors work at. It has been said that slideshows should be made for the display resolution available for showing. However, if your computer can handle the larger files then even with present projectors it seems the image quality on the screen should be slightly better with larger files, and especially if zooming is used. Or am I missing something?

John.

[alrobin]

John,

One reason for resizing files to fit one's monitor resolution is that if larger files are used, then PTE (and your computer) have to make the decision on how to make the reduction in size for you. Most of the time they do a pretty good job in this, but eventually the image will end up being 1024x768, or whatever resolution you are using in the projection ( or viewing on the monitor ). But, it would be better if you performed this reduction in size personally, ahead of time, in a high-quality image editor, with more control over the process.

However, if your viewing equipment will handle higher resolutions, then by all means it is better to use larger images.

As far as zooming and panning are concerned, a larger image is better so that the portion being displayed will be of the same quality as it would be had you cropped the larger image down to the size shown by the projector or on the monitor. It is easy to calculate what this larger size should be, by using proportionality calculations based on the total dimensions being panned or zoomed compared with the size of the image seen at any instant in time.

[Ronniebootwest]

[quote It is easy to calculate what this larger size should be, by using proportionality calculations based on the total dimensions being panned or zoomed compared with the size of the image seen at any instant in time.

[Guest Techman1]

I magnified the larger image by 100% for detail and to bring the smaller one up to the same viewing size had to magnify it 200%. As these are now viewed at the same size image on the screen it was easier to see that the larger image had the best quality.

John,

If you reduce the file, you might want to apply an unsharpen filter to the smaller image to make it appear sharper. Additionally, you shouldn't try to view an image at greater than 100%, because you will begin to see jaggies (jagged edges in an image). Try viewing the smaller resolution image (1024x768) at 100% and then size the larger resolution image at whatever size (< 100%) needed to view them at approximately the same size.

I hope this helps a little.

Regards,

Fred

[thedom]

It is easy to calculate what this larger size should be, by using proportionality calculations based on the total dimensions being panned or zoomed compared with the size of the image seen at any instant in time.

Blimey Al! What does all this mean?

Ronnie,

I'm not sure but think it means that if you apply a zoom 125% on a picture B, to maintain the same image quality as an image A displayed 100%, the size of image B as to be 125% of image A.

Ex : image A = 1024 - 768

=> image B = 1024 x 125 % - 768 x 125% => image B = 1280 x 960.

[alrobin]

Blimey Al! What does all this mean?

Ronnie,

I tried to keep it simple, but basically it means that if you want to pan to an area completely adjacent to an image, but no more, then the resolution of the source file should be twice the resolution of the monitor, in both the vertical and horizontal directions.

Dom's explanation is correct, in the case of "zoom". If the zoom is 200%, then the vertical and horizontal resolution of the source image, in pixels, should be twice the resolution of the intended monitor, both vertically and horizontally.