Preferred image format

When you export to a .books, the images will be converted to a .jpeg and recompressed by the app.

Below are the images that are stored/used in a Test.ibooks.

The original jpeg test image was 269 KB and the original PNG image was 1.6 MB. Both images are the same size, 1024x768.

Since the app recompresses (all of the) images on export you might as well use PNG images in the .iba

I unzipped the .ibooks file (that was exported from menu bar)

and checked the images in the assets folder

and the JPEG stayed a JPEG and the PNG statyed a PNG

Which appears to be differnt then what happened for you.

My bad...

If you look at the content, the .ibooks is built using xhtml and CSS just like a web page.

I have heard that javascript can also be used. I haven't checked this out. Epubs are built using xhtml, javascript and CSS.

With iOS, standard screen resolution is 72dpi/ppi while retina screens are 132.

You might want to make a test book with several images to find out how your particular resources work out on an actual device.

dpi/ppi resoution dosn't realy matter.

a 1024 x 768 pix image at 20 dpi is the same as a 1024 x 768 at 300 dpi.

same file size, same file compression. The only difference is when placed in a layout program like InDesign.

PNG are lossless, will tend to be a lot larger in file size, and work better for graphics and type, much the way GIFs were originaly.

I'm surprized that the PNG doc was a smaller file size. In my test the PNG doc was larger file size then the same with jpg.

JPG is lossy, based on compression, which will alter file size in bytes and are better for photos.

also JPGs do not support transparency, PNGs do.

Saved from photoshop, 1024x768 image as PNG 24 was 283 K and as a JPG (high quality/low compression) was 51k.

Ipad screen is 1024 pix x768

images shoud be pre sized in photoshop etc. just as you do for the web. ie. you shouldn't inlarge or reduce in IBA.

>dpi/ppi resoution dosn't realy matter.

Of course it does. It pays to be aware of and apply the specs for the target platform. You're not building a website...you are creating an iOS specific app.

The build process will bring down anything that that exceeds the spec....load it up with images that are too high and you'll slow that process. Larger books will take longer to build, etc. iOS cares what you feed it and won't sharpen low-res images.

I don't think it does.

the fle is the same.

change the dpi resolution of an image in photoshop with out resampling

and the file size in bytes do not change, the quality of the image does not change,

it only affects the size it is "displayed" at when placed in InDesign.

a image that is 1024 by 768 at 5000 dpi is the same as a 1024 x768 image at 72dpi.

The absolute pixel resolution (the 1024 x 768) is what matters, the dpi and the size in inches do not matter.

Place a 1024 x768 (20dpi) and convert it to 1024 x 768 (300 dpi) with out resampling

and drag them both into IBA and they are the same.

The fact that one is 51 inches wide and ther other is 3.4 inches wide doesn't matter.

they are the same image, both are 1024 x 768,

their DPI and size in inches do not matter.

If you think a 32 dpi image will be displayed identical to a 132 dpi image, you're mistaken.

I don't know how you're testing, or if you have any experience with apps, but again, this isn't website rules. Cater to the platform - iPad - in all cases.

I'll be happy to quote iOS documentation, within the NDAs of course, if you like.

dragged into ibooks author

screen shot

image on left is 72 dpi image on left is 500dpi

they are the same.

Photoshop info

for both

if is to fill the ipad screen when in landscap it should be 1024 pixels wide.

anything larger is a waste of fie size and it will be reduced with out sharpening.

it should be the exacct size (in pixels) that you want it on the ipad screen.

ie reduced in photoshop, sharpened etc.

then brought into IBA at actual size

KT,

Sorry,

I don't mean to argue with you.

I think it maybe that how we determine an images DPI is different.

I'm talking about settings in Photoshop before importing into IBA

since we are talking about best formats for images for IBA

You may be talking about DPI at a fixed size in inches, as in the final display on the ipad.

Yes, 20dpi at 10 inches vs 300dpi at 10 inches makes a difference.

but the image pixel dimension will be different too. and thats my point,

that the dimension in pixels is what is important.

As far as testing, I'm using ibooks Author (and an ipad)

see screen shot sent earler

I set my DPI in photoshop (or don't)

the DPI is just a value relative to the pixel width and image size in inches

change the size in inches and the dpi will change. change the DPI and the size in inches will change.

If you change the DPI AND keep the size in inches the same you are resampling the image and thus changing the images dimensions in pixels. (the number that matters)

There may be some programs that resample an image apon import based on its DPI setting. I haven't come across any and IBA does not appear to do that.

iPad is 132 dpi

iPhone Retina display is 326 dpi

iPhone regular display is 72 dpi

I think it is best to import images at the pixels dimension they are going to display at

and not reduce or enlarge the image in IBA

So if you want a photo to be 5 inches wide on the ipad it should be 660 pixels wide

and the DPI settings in photoshop can be what ever.

I'm sure we are talking about the same thing, just from different directions.

Cheers,

B

>I'm sure we are talking about the same thing, just from different directions.

I agree, and just to follow up on this, your rational is correct as stated. An Apple Engineer on the iOS Developer forums explained earlier this yeat why anything over 72 is wasted and also said that dpi/ppi is meaningless in this context.

An easier and more reliable way is using Zipeg. http://www.zipeg.com

It's useful to be able to get at some of these assests for amending them, but to be honest I wouldn't tinker with anything internally. It can cause issues.

Zipeg the iba file, copy out the assets you want to change, change them and open the .iba in IBA again to re-import the updated assets. I certainly wouldn't try to update an image within the .iba file and assume that the .iba file would just be OK with that.

PNG