unsharp pics aft resizing

[jamcrky]

Hello everyone..........I have been using irfanview for the past several years and never had a problem till recently.....
I have been using the batch conversion under file......and now after resizing many of the pics appear to be unsharp......some appear to be over sharpen...I have tried several different setting in the advance mode and the results are always the same.....I had check them in PS and they are sharp....

I think this may have started when I got a new camera Nikon D80 but not sure.......he a copy of what I am takling about

one other question....Do my jpeg files degrade everything I tried to resize ???

http://i.pbase.com/o6/20/213220/1/100158434.kQ1EwMY2.resizedDSC_1235.JPG

Thanks in advance for all the help and info .....Jim

[Leif]

http://i.pbase.com/o6/20/213220/1/100158434.kQ1EwMY2.resizedDSC_1235.JPG

Forbidden

You don't have permission to access /o6/20/213220/1/100158434.kQ1EwMY2.resizedDSC_1235.JPG on this server.
Apache/2.0.58 (Unix) Server at i.pbase.com Port 80

[j7n]

403 Forbidden

It's a stupid HTTP_REFERER protection.

Do my jpeg files degrade everything I tried to resize ???

Yes, JPEG is a lossy compression and files should be saved only once to this format. If you repeatedly edit a JPEG file, its quality will degrade.

From the screenshot I can see that you're doing Resize instead of Resample. Resize is a primitive algorythm, similar to whats being used if you zoom in and out. Go to the Image -> Resize/Resample dialog and do one operation with the correct parameters: Lanczos filter. After that this choice should be preserved also in the Batch dialog.

[jamcrky]

resizing

Thanks again will try it tonight....I'm glad I keep the pics on my memory card so I can upload em again as they probably are degraded after many attmept s trying to resize......
I just have one more question.....you had talk about looking at my screen shot and gather the info from there how do you look at the screen shot from a pic that I had sent...never knew howto do that ......

and thanks for the step by step instructions......I really need that

Jim

[j7n]

I should've said that I looked at the picture. Dunno why 'screenshot' came to my mind.

But anyway the picture is not unsharp. It's overly sharp, so that it's really hard to tell if pixel resize was done or and excessive sharpening was applied to it. Be careful with the option "apply sharpen after resample".

Also resize of any kind should be done only once. If you need a different size, go back to the original and do it again. Always keep the originals.

[jamcrky]

resizing

First of all thanks for your time and help.....I follow your directions brought a picture in imaage resize/resample using lanczos and the quality is excellent...but now I'm lost where do I go from here ....if I want to do a batch resize/resample for lets say 200 pics....I went to file>batch conversoin rename and everything is the same as before???......I read some of the stuff in the help menu but still cant make sense out of it.....

Thanks again Jim

[j7n]

the quality is excellent...

Now we are getting somewhere.

In batch dialog, when you click Advanced options, you need to activate the checkbox called "Use Resample function (better quality)". I just noticed that it's off by default.

[jamcrky]

resizing resample

yes we are getting somewhere thanks to you......

Ok I just want to carify all the steps just so I have it clear in my own mind

go to image>resize/resample>lanczos>select size which in my case I am using 800x600>preserve aspect ratio>applied sharpen after resample (I will check to see if this is better or not to use)>dpi defaults to 72> then OK

then file> batch conversion/rename>advance>use resample function>(should I also click on preserve aspect ratio or is that already done in the image steps)>the leave everything else as is>look in get pictures and add all>set output directory>then start batch> and I'm good to go......

By george, if this is correct, I think I have it..........

I may be a little old and slow, but I do eventually gets things right

Now one final question, and I will stop being a pain in the butt.....
Does resampling improve quality? The reason I ask is the when I did a couple of pictures in the image steps the quality seem better than the orginal..

Once again, thanks so much, ur the best........Jim

[j7n]

You don't need to go to Image -> Resize before each batch, only to experiment with different quality settings and finally settle to one. DPI can be set to any value, it has no meaning in this context.

Preserve aspect ratio allows you to set only one dimension of the picture with the other being computed automatically using the ratio between width and height.

For example we start with 1280*1024 pixels (5:4 aspect ratio).
If you enter 800*600 the image will be distorted (4:3 now).
If the aspect ratio option is activated, you enter 800 and 640 fills in on its own (800*4/5=640).

Downscaling (decreasing the size) improves subjective quality because it increases the signal to noise ratio (SNR) at the expense of resolution. Also since you can no longer see each individual pixel, your brain believes that there are more details in the scene, and if you could move closer to it the additional details could be revealed. Pics from a digital camera usually look poor at their original res, because the camera internally upsamples the data by a significant factor. But these improvements are an illusion only. Keep the originals.

When you do the batch conversion, pay attention to the selected output format. By default it is set to poor quality - JPEG @ 80 units, 4:1 color subsampling. You'll want to increase these parameters.

Now one final question, and I will stop being a pain in the butt.....

Don't worry, you weren't.

[Sam_Zen]

Imo it's the wrong order to do a resize, and then apply the sharpen function.
Resizing is smaller most of the time, so there will be a loss of pixels, because there are simply less available to make the picture.

So it's better to 'pimp' the picture first with a sharpening, before doing a resize, where you will loose single pixels anyway.

[jamcrky]

rsizing

Thanks much for all the info.......will try it tonight and asorb all this information..........Jim