Photoshop multiple image resizing tool - dpi?

[Ari]

I've been looking for a way of multiple resizing images, and my Photoshop Elements 10 has this facility.

My question is, what should I set the dpi to? On the original images (some taken with a Nikon D7000, some with a D600 and some with a Sony RX100) this seems to vary. The Nikons are 300dpi, the Sony 350dpi.

Any thoughts?

[Ari]

Just tried it on 150dpi (as it reverted to that) and it's putting lines in the sky where the colour gradually gets darker further up the picture on the Sony images.

[The_Jackal]

DPI only applies if you are printing to real media like paper. For digital purposes it has no meaning.
I think 200+ dpi is recommended for printing

[Rogue86]

As above, generally 300dpi is print, 72dpi is web.

[LongQ]

When you say "Multiple resizing" do you mean making much bigger by resizing multiple times?

If so .... there are many opinions about how to approach that challenge and the approach may depend on which application you use.

[boyse7en]

Rogue86 said:

As above, generally 300dpi is print, 72dpi is web.

True, but for really large-format printing it can be a lot less.

I've just designed some 3m x 8m banners for an exhibition, and the images required to output that were at 75dpi.

[Ari]

LongQ said:

When you say "Multiple resizing" do you mean making much bigger by resizing multiple times?

If so .... there are many opinions about how to approach that challenge and the approach may depend on which application you use.

Sorry, didn't explain myself well. I'm actually doing the reverse. What I want to do is take a bunch of my full sized images and cut them down to 25% of the size for emailing or whatever. So I'm copying the ones I want to resize to another file and want to select them all and resize them in one go rather than tediously opening Paint, clicking 'resize', choosing a size of 25%, OKing it, saving it, and moving on to the next. That's fine for one or two (and works well, its what I've used in the past) but a but of a pain when I want to do 20 at a time (hence wanting to resize multiple images simultaneously).

The Elements 10 method works very well, except for these colour lines where the colour fades, which I am guessing is something to do with this DPS thing (Paint doesn't seem to have this).

[LongQ]

Ari said:

Sorry, didn't explain myself well. I'm actually doing the reverse. What I want to do is take a bunch of my full sized images and cut them down to 25% of the size for emailing or whatever. So I'm copying the ones I want to resize to another file and want to select them all and resize them in one go rather than tediously opening Paint, clicking 'resize', choosing a size of 25%, OKing it, saving it, and moving on to the next. That's fine for one or two (and works well, its what I've used in the past) but a but of a pain when I want to do 20 at a time (hence wanting to resize multiple images simultaneously).

The Elements 10 method works very well, except for these colour lines where the colour fades, which I am guessing is something to do with this DPS thing (Paint doesn't seem to have this).

Ah. That was my initial interpretation but I decided I was wrong.

The answer I have is - dunno - but I think it is more likely that the banding is to do with compression in the jpegs than dpi which in general one can sort of ignore other than for file sizing purposes when producing output for on screen display or for printing - again with file size being the pertinent consideration if there is one.

The banding, I would assume, is to do with compression of the files.

If you were enlarging I would suggest going 16bit and enlarging in small steps OR finding some software that is comfortable taking big steps.

For compressing ... not sure.

I would do a search on't net to see what comes up ..... unless some kind person here has the answer.

[Simpo Two]

What you need is 'actions' and 'batch' - but I don't know if PS Elements has those.

Whatever, set dimensions in pixels; dpi is meaningless on a computer. I commonly use 800 x 600px, and compress (file size not image size) as required in the Save As process.


NB: If you're not too fussy about quality, try right-clicking on an image - my contextual menu includes 'resize' and has a few options in it.

NNB: 'colour lines where the colour fades' sounds like too much compression on a colour gradient, eg a blue sky.

Edited by Simpo Two on Wednesday 4th February 21:13

[Ari]

Yes you are right, it's most obvious in the sky.

There's no resize button when I right-click, which is frustrating as it used to have in XP.

I'm not using the dpi to resize, I'm selecting 25% of original size which gets me to the kind if size I want. However there is this area where you select dpi, up to 600dpi (which I tried initially as I figured that was the best quality).

I can resize with Paint by clicking 'resize' and selecting 25% and it works perfectly, but means doing each image one by one, and I have about 200 to do! Hence trying to batch resize, which Elements 10 will do, but with this weird colour fringing thing.

[LongQ]

Ari said:

Yes you are right, it's most obvious in the sky.

There's no resize button when I right-click, which is frustrating as it used to have in XP.

I'm not using the dpi to resize, I'm selecting 25% of original size which gets me to the kind if size I want. However there is this area where you select dpi, up to 600dpi (which I tried initially as I figured that was the best quality).

I can resize with Paint by clicking 'resize' and selecting 25% and it works perfectly, but means doing each image one by one, and I have about 200 to do! Hence trying to batch resize, which Elements 10 will do, but with this weird colour fringing thing.

Experiment with the compression - especially if it allows you to use different compression methods.

[Simpo Two]

Ari said:

Yes you are right, it's most obvious in the sky.

There's no resize button when I right-click, which is frustrating as it used to have in XP.

Heh, I use XP Pro!

I guess %area works on pixels, so if 25% is right for you, carry on.

Ari said:

Hence trying to batch resize, which Elements 10 will do, but with this weird colour fringing thing.

That will be compression. Can you set the amount of compression that's applied? If you've set it to 'resize for web/e-mail' that would explain it.

[Ari]

Ah. I've not found a compression setting, I'll have another go.

I'm still unclear on which of the dpi choices I should be selecting though...

[LongQ]

Ari said:

I'm still unclear on which of the dpi choices I should be selecting though...

It doesn't matter. Unless something odd happens in Elements it only affects the calculation for the nominal print size that the settings would support. Or, if for screen viewing at 72 dpi, how big the result will appear to be on a typical screen - except that dpi (dots per inch on printed output) and ppi (pixels per inch on screen displays) are not truly directly comparable these days. But as a guide they should be OK.

[Simpo Two]

Your photos are going to be seen on a screen made of pixels. Therefore pixel dimensions (X x Y) are what matters.

DPI simply scales those pixels across a piece of paper - in other words an image 3,000px wide at 300dpi will be 10" wide. Reduce the dpi and it just takes up more paper. A digital image has no inches.

[budfox]

Firstly. Download Irfanview. It's free, brilliant and will batch resize any amount of images in no time. You can rename them at the same time.

Secondly, the banding you are seeing is called quantising. It happens with very subtle changes in colour as images are compressed. A quick Google will reveal all.

[Ari]

I'm really amazed Photoshop cannot do this. This is the result of a resize, look at the colours on the wing!





I also tried it with Paint, works perfectly.

[Ari]

budfox said:

Firstly. Download Irfanview. It's free, brilliant and will batch resize any amount of images in no time. You can rename them at the same time.

Secondly, the banding you are seeing is called quantising. It happens with very subtle changes in colour as images are compressed. A quick Google will reveal all.

I'll give that a go, thank you.

As to the quantising, what I don't understand is why a program like Photoshop has an issue when Paint can do it perfectly.

[rich888]

Ari said:

I've been looking for a way of multiple resizing images, and my Photoshop Elements 10 has this facility.

My question is, what should I set the dpi to? On the original images (some taken with a Nikon D7000, some with a D600 and some with a Sony RX100) this seems to vary. The Nikons are 300dpi, the Sony 350dpi.

Any thoughts?

One of the easiest methods of resizing images that I use is Google Picasa which is a free download from Google, once it has scanned your images on your HD it displays them as thumbnails in a flat format by date order, so even images lost for years buried within folders within folders within folders are easily viewed.

You can select one image or more, or indeed the entire folder in question, click on export, then select the pixel size you require from the slider (320px, 480px, 640px, 800px, 1024px, 1200px, 1600px - or enter your own size), it can also rename the resized images if required to save confusion at a later date. You can also add a watermark to these images if you wish.

Comes highly recommended and is pretty much idiot proof!

[MysteryLemon]

Looking at the examples you are showing above, it's not photoshop that is at fault resizing the image, its the compression you are applying to the file when saving it out.

There are also different resizing algorithms available in photoshop which can produce different results when downsizing or upsizing.





Also, as said above, DPI is irrelevant unless you are sizing the image to a specific print size. A 3000x4000 pixel image at 300dpi is still a 3000x4000 pixel image at 72dpi. The difference is that a printer will see the 300dpi image as a 10in x 13.3in image and the 72dpi image as a 41.6in x 55.5in image. The input file is exactly the same and unless you are printing it, it doesn't matter.