When you select the image in ID, what is listed in the Info Panel under "effective ppi"?
Actual ppi is 72. Effective ppi is 262.
Okay, now here is the weird thing. I was able to make it look okay in ID, but it STILL exports to ePub jagged and semi-pixilated. The way I made it look better in ID, not perfect, mind you, but better, was to create a new file in Photoshop, flatten the old file, select and drag the flattened layer into the new file, flatten again, and save as a JPG. Then replaced the old with the new.
Honestly, I don't know if that was the reason for the difference. Just what I tried. Again, everything else in the ePub looks good. I cleaned up the .opf, .html, and .css to match what I did with the first ePub that validatated perfectly.
I don't do ePub, so I don't know for sure waht resolution gets used, but I think what's happening is yor images are being downsampled on export, probably from the effective 262 to 72 ppi, which would throw away about 2/3 of the image data and would cause the jaggies.
What does your image look like in Photoshop if you reduce it to the dimensions you are using it in ID and save at 72 ppi? I bet it introduces the same jaggies in Photoshop.
I think you're right. The image is getting downsampled a lot, but I don't know why. I opened the image folders inside the ePubs of each of my projects to compare.
In the first project, where the cover image was successfully rendered, the original image was 1.6MB, which ID reduced to 369KB on export.
In the second project, which is having problems, the original image is 3MB, which ID is reducing to 147KB on export, a drastic downsampling. I even tried reducing the image in Photoshop to the same 1.6MB size as the first project image, just to see if ID couldn't handle the larger file size. It made no difference.
Why is this happening, and how can I stop it?
When you go to export for Epub there is an option for images.
Go to JPEG Options and select Image Quality "maximum"
There are settings for downsampling and compression in the export dialog, I'm sure, but this may be something you can't avoid in your epub. It's best to place your images at 100%, I think, in this workflow, and you may just be working too small for hard edges that slope to look good.
Okay, on export used the Maximum setting. Sure enough the file size doubled, and I thought for certain that the problem was solved. No such luck. Just as jagged. The original file seems of generous size for an ebook, 1852 x 2628, larger than the first project and that cover came out wonderfully.
When you say place at 100%, how you mean? I didn't think it mattered when it goes to ePub. I used Cmd + D, click on the page in ID, the image loads. I only resize it on the page for my own benefit in layout.
Exhausted now, been up all night with this. Appreciate everyone's help. Will check back later today.
When you say place at 100% how you mean? I didn't think it mattered since it was going to ePub anyway. I used Cmd + D, click on the page in ID, the image loads. I only resize it on the page for my own benefit in layout.
I mean you don't want to scale the image in ID. The pixel dimensions of the saved image should be the same as the number of pixles required to place the image at the intended size and resolution. When you scale, you are either throwing away pixels or make up new ones by interpolation. Your epub is basically just a web page, and it doesn't care about the resolution of your image, just how many pixels are in it. Any non-vertical or non-horizontal line must be made by stair-stepping around pixel edges -- you can't use half a pixel -- and the more pixels you have available for that stair, the less jagged the appearance will be on screen.