Advice on Sizing PNG Files

[TonyFalla]

I am trying to set up an AV Show, using 5.5 Beta, part of which I want to use O&A on some newspaper clippings which I have scanned in. The originals were scanned in at 600 dpi and saved as TIF files, after which I did some manipulation to get what I required and then saved as PNG files. I loaded these images into my O&A sequence and then had all sorts of problems, PTE crashed, Preview stopped responding, I then realised that the PNG images were very large 5 - 15 MB so it was a problem of my own making as they were still 600dpi.

I then got my PNG images and in Photoshop used the image size command to reduce them to 100 dpi which gave me much more reasonable size images. I now find however that when I load the 100 dpi images they have lost definition and appear to be slightly blurred.

Can anybody point me to any articles or offer advice on how to scan in newspaper clippings and create small PNG files without this loss of defintion?

Tony Falla

[Maureen]

Hi Tony

Sut Mae?

Are you planning to do any printing?

I ask because the only reason to talk about dpi (dots per inch) is if you are a print worker.

If you are in the world of the projectionist ie creating AVs for monitors, televisions, projectors - completely forget dpi (the Myth of 72 dpi has been covered here for many moons and can be viewed at http://www.scantips.com/no72dpi.html and no doubt Ken will paste a lot of links to help you too).

You do need to concentrate on the pixel sizes of your images.

Are you still working at 1024px by 768px or have you upgraded to future proof your work for HD to 1920px by 1080px ready for the new projectors currently available?

You need to tell us what size resolution ie pixel size you are creating your PTE show at the moment.

Then create the png image larger than that so it will work smoothly in your O&A sequence.

By all means scan the newspaper at the biggest size you can so you have a really sharp image. Then resize with Photoshop's crop tool leaving the dpi box blank.

We held an RPS AV workshop covering this cropping in South Wales last year and hope to do another soon. Meetings are open to non RPS members too.

Hope this helps.

[Ken Cox]

Tony

see

http://www.scantips.com/basics04.html

http://www.scantips.com/basics2f.html

http://www.scantips.com/basics4f.html

http://www.scantips.com/resolut.html

http://www.scantips.com/basics9jb.html

http://www.scantips.com/basics1e.html

http://www.scantips.com/interpol.html

and the best in my opinion

http://www.scantips.com/basics6b.html

I have found that this site has the answers to most scanning questions - in fact i bought his book

ken

[fh1805]

Tony,

One point that hasn't been mentioned is that, whenever you resize downwards in Photoshop, you always lose some definition and so will have to get that sharpness back. After doing the resize as described by Maureen you then need to apply Unsharp Mask. In a recent post elsewhere on the forum Barry Beckham suggested using Amount=200%, Radius=0.3 pixel and Threshold=1. I find this a good start point. The only parameter I find I need to change is the Amount. Sometimes 200% gives an unpleasant effect and so I reduce it in steps of 25 until I find a setting that I'm happier with for that particular image.

I use quite a lot of old black and white images in some of my sequeces and find that these often require less than 200% whereas modern day colour digital images seem very happy to accept 200%.

[thedom]

Hi Tony,

Is there a particular reason why you want to keep your scan as a PNG file ?

PNG file might be huge.

If you do not need transparency (main reason for using png files), you could save your file as JPG file, keep a big resolution and decrease the weight of your image.

An other alternative would be to save it as a GIF file. I think this format is quite appropriate to keep a good resolution for text.

May be you could try both and see which one gives the best result ...

[TonyFalla]

Thanks for all the replies they have been most helpful and I can now see how I can improve the quality of the scans.

I apologise for typing dpi when of course I meant ppi, the senility must be worse than I thought! I was however using this to reduce the file size of my images, I know I could have cropped the image to a fixed pixel size and could have achieved this by either the Crop Tool or the Image Size Tool and agree that the Crop tool is best for this if you want all your images to be the same pixel size. In this case however all of my scans were different sizes as I was scanning anything from a small headline to a half page article. I had scanned them all at 600ppi therefore it was sensible and convenient to reduce them using the ppi setting as I would then retain the relative size of each image.

It so happens I produce all my shows in 4:3 format as that is the format for the projector I use and on top of that I personally dislike the 16:9 format.

The articles on scanning that Ken informed me about I have found very useful and have shown that the poor resolution I am getting was due more to the way I was scanning than the degradation of the image due to resizing. I am going to try rescanning and see how I go from there. I do need the PNG transparency for the AV I have in mind.

Once again many thanks for the help

Tony Falla