Image's Document Size

[goddi]

Greetings,

I have a question that has to do with reducing the file size of images I use in PTE. I have been using a program that is no longer available, but it has been an easy way for me to batch-reduce the file size of my images I use in the slideshows.

The program I have been using is Net Graphics Optimizer. I use it to batch-reduce the images at ‘80’ and I tell it to keep the original dimensions. However, I recently discovered that, when I look at the image size in Photoshop, it indicates the image’s Document Size is 3.333” x 2.5”, not 13.333” x 10” as is the original size.

I did a test using InfanView and also reduced the same image at ‘80’. But InfanView kept the Document Size at 13.333” x 10”. Both are at 300 resolution.

So here is my question: I put both of these images in PTE and I cannot tell the difference. How can a 3.333” x 2.5” image (97Kb) be as good (sharp) as a 13.333” x 10” image (854Kb) in PTE?

Thanks… Gary

[fh1805]

Gary,

You are tying to asses the quality of a Displayed image by using the attributes of a Printed image.

The dimensions in inches that you are seeing from Photoshop are the maximum size that Photoshop is recommending you print your image at. When tryimg to assess the visual quality of a displayed image the numbers that matter are the dimensions in pixels (e.g 1024x768, 1920x1080 or whatever). After this, the other value of any significance is the level of JPEG compression.

I don't know whether States-side you have the saying about comparing apples and oranges. If you do, then you are trying to assess the quality of "apples" by using a standard that is only appropriate for "oranges"

regards,

Peter

[davegee]

What are their respective pixel dimensions?

DG

P.S. Peter beat me to it.

[goddi]

Gary,

You are tying to asses the quality of a Displayed image by using the attributes of a Printed image.

The dimensions in inches that you are seeing from Photoshop are the maximum size that Photoshop is recommending you print your image at. When tryimg to assess the visual quality of a displayed image the numbers that matter are the dimensions in pixels (e.g 1024x768, 1920x1080 or whatever). After this, the other value of any significance is the level of JPEG compression.

I don't know whether States-side you have the saying about comparing apples and oranges. If you do, then you are trying to assess the quality of "apples" by using a standard that is only appropriate for "oranges"

regards,

Peter

======================

Peter and Dave,

While it is obvious that I can't tell the difference between apples and oranges, it is still a wonderment in my mind that PTE can show the same images that have different resolutions but appear to be identical in quality in the slideshow. You mentioned the pixel dimensions. I thought by giving the different file size of each image, that might be a clue. The pixel dimension for the 97Kb image is 1000 x 750 and the pixel dimension for the 854Kb image is 4000 x 3000. And both look identical in PTE. What else puzzles me is if both were reduced using the same '80' setting, why are both so different in final file size? I would think they would both end up the same size. Maybe each software has their own '80' algorithm?

I would stick with my old software that gives me the smaller file size without any difference in quality when viewed in PTE when compared with the larger file sized image. But it seems that the different pixel dimension would give some kind of quality difference in PTE...but I don't see it. If none of the above makes any difference in the final quality of the slideshow, what does when you are trying to reduce the size of the final PTE slideshow (given the same image)??? Both were created in PTE at 1920 x 1080.

I just created an MP4 of the slideshow and I could not see any quality difference between these 2 images when played on my 40" LED TV.

Gary

[nobeefstu]

Gary,

Why dont you upload or attach zip of the two images for better file comparsion and inspection.

There seems to be another image compression/multiplier involved for the smaller size image ... it may be that the Net Graphics Optimizer program is optimizing for the web whereas PS and infraview are not even though you are using a 80 setting. Its exactly 25% (using multiplier of 4) smaller than that of the larger image.

(1000 x 750) pixels x 4 = 4000 x 1000 pixels or (3.333 x 2.5) inches x 4 = 13.333 x 10 inches.

Are you optimizing for the web in PS also ?

[Rickl]

Hi Gary,

Isn't jpg compression amazing!

As Peter mentioned, there are two issues here... image resolution and compression.

The pixel dimension for the 97Kb image is 1000 x 750 and the pixel dimension for the 854Kb image is 4000 x 3000

Your final image was 1920x1080. So in the small image case, PTE has to enlarge (actually interpolate) your 1000x750 image by a factor of two for the slideshow. In the larger image case PTE has to reduce the image size by approximately 2 to fit the 1920x1080 format.

I'm pretty sure that you should be able to detect differences between the small and large images if you examined them carefully. I use Faststone as my image viewer, and it allows you to compare images side by side. Bear in mind that the smaller image has to be enlarged by a factor of two to compare side by side... I think image deterioration should be visible then.

But it constantly amazes me the quality of images PTE manages to put on the screen, even when smaller images have to be enlarged...

On the sizing issue in your original message, note that your 40" TV is displaying an image that is 1920x1080 pixels in size. A printed image that size, assuming a minimum of image quality of 240 pixels per inch would require an image size of approximately 8400x4725 pixels according to my rough calculations. That is the point Peter was trying to make when comparing display vs printed size...

Hope this helps,

Dick

[goddi]

Gary,

Why dont you upload or attach zip of the two images for better file comparsion and inspection.

There seems to be another image compression/multiplier involved for the smaller size image ... it may be that the Net Graphics Optimizer program is optimizing for the web whereas PS and infraview are not even though you are using a 80 setting. Its exactly 25% (using multiplier of 4) smaller than that of the larger image.

(1000 x 750) pixels x 4 = 4000 x 1000 pixels or (3.333 x 2.5) inches x 4 = 13.333 x 10 inches.

Are you optimizing for the web in PS also ?

=================

nobeefstu...

I am slowly putting my brain in gear. In NGOptimizer, it has a place to tick to keep the original size of the image when I reduce it using '80'. I had totally forgot that that option does not actually work. Even if ticked, the image comes out as a 3 x 2 dimensioned image. So that is why the file size is so much smaller than InfanView, which keeps the original size of the image. Ok...with that said, PTE seems to be doing a fantastic job because I can not tell the difference between the small image and the larger image when displayed as an MP4 show on my 40" LED.

No, I have not tried optimizing for the web in PS. NGOptimizer was just so easy to use.

For what it's worth, I have attached the two images.

Gary

Two Images.zip