The Reading Vent & Rant Thread

[JSWolf]

Originally Posted by John F

Is that a typo? Did you mean to say you do lossy compression?

Not a typo. Once the image is recompressed, it is then losslessly compressed from there.

[John F]

Originally Posted by JSWolf

I use a size of 1680 lines and I keep the aspect ratio correct. and I losslessly recompress the cover with a value of 70%. I don't notice any difference in quality and the cover is smaller but large enough.

Originally Posted by JSWolf

Not a typo. Once the image is recompressed, it is then losslessly compressed from there.

I may be a little ignorant on image compression, but doesn't "70%" apply to lossy compression (lossless compression doesn't include a percent). At least that is the way it works when I use the calibre editor to compress (jpeg) images.

[JSWolf]

Originally Posted by John F

I may be a little ignorant on image compression, but doesn't "70%" apply to lossy compression (lossless compression doesn't include a percent). At least that is the way it works when I use the calibre editor to compress (jpeg) images.

It's both lossy and lossless. Lossy for the recompression with 70% and lossless after that to make the image an even smaller size.

[John F]

Originally Posted by JSWolf

It's both lossy and lossless. Lossy for the recompression with 70% and lossless after that to make the image an even smaller size.

Thank you for the clarification. I'm going to start doing the additional lossless compression.

[JSWolf]

Originally Posted by John F

Thank you for the clarification. I'm going to start doing the additional lossless compression.

Your very welcome. Happy to help.

Just a quick note. I don't notice any difference in the image quality with a 70% compression.

[nabsltd]

Originally Posted by ownedbycats

Yeah, you take care. The photographs that I'm shuddering at have the book at an awkward angle, the picture blurry, and the camera flash on.

At least the awkward angle problem can be fixed with a few choice filters (skew, perspective, etc.). Recently, I've gotten a few good covers from various Calibre metadata sources where that was the only problem.

I just drag a PNG drawing of a grid to the file and make it the top layer. Then, twist and distort until the book sides are aligned and the text isn't sloping. Toss the grid and save.

[ownedbycats]

Originally Posted by Aleron Ives

You do know that 640 is less than 1000, right?

As I said, generated covers are just the title and author. So the resolution matters less.

[John F]

Originally Posted by JSWolf

It's both lossy and lossless. Lossy for the recompression with 70% and lossless after that to make the image an even smaller size.

Originally Posted by John F

Thank you for the clarification. I'm going to start doing the additional lossless compression.

I tried it on a couple of ebooks, and I'm seeing some interesting behaviour using the calibre editor.

I do a lossy compression and then a lossless compression in the same editing session, and the lossless compression says it couldn't compress any further. and I exit.

After that, every time I do another lossless compression, it reports it is able to compress the cover image for the same amount (this is doing a compression and then exiting (and saving)).

[ownedbycats]

Yeah, I'm a bit baffled by all this. Compressing an already-compressed file usually not do much, or even sometimes paradoxically makes the file bigger.

[John F]

Originally Posted by ownedbycats

Yeah, I'm a bit baffled by all this. Compressing an already-compressed file usually not do much, or even sometimes paradoxically makes the file bigger.

I don't know much about calibre, but my WAG is that when you start editing, calibre replaces the cover image in epub file with calibre's cover image.

[j.p.s]

Originally Posted by ownedbycats

Yeah, I'm a bit baffled by all this. Compressing an already-compressed file usually not do much, or even sometimes paradoxically makes the file bigger.

Various JPEG optimization applications use more efficient representations of the encoding tables and better encoding types. The actual compressed image data does not change but the total file size does. JPEG images often contain metadata, comments, and other extraneous information. Removing some or all of that also reduces file size.
https://en.wikipedia.org/wiki/Jpegtran

Decompressing lossily compressed data then lossily recompressing it will result in additional loss from the original data.

Compression algorithms usually make assumptions about the nature of the uncompressed data. It is not unusual for file size to increase when there is not a good match between the assumptions and the actual data. Examples different algorithms being better for different data types are JPEG for photographs and PNG for regions of same color and simple line drawings.

Compressing is an exercise in reducing redundancy. (Nothing compresses better than all zeros.) Well compressed data has little or no redundancy, so the overhead of describing the compressed data increases the file size when trying compress already compressed data. (Try compressing random noise.)

Using general purpose compression on specially compressed data can result in a smaller file than either method used alone. For example, zipping a JPEG made from a BMP might be significantly smaller than a zip of the BMP.

[Aleron Ives]

Originally Posted by John F

I do a lossy compression and then a lossless compression in the same editing session, and the lossless compression says it couldn't compress any further. and I exit.

What image format(s) are you using? JPEG already has both lossy and lossless compression: the final lossless phase is based on Huffman coding and tries to optimise the remaining data after lossy compression is complete.

[Quoth]

Originally Posted by John F

I don't know much about calibre, but my WAG is that when you start editing, calibre replaces the cover image in epub file with calibre's cover image.

I'm sure that's a setting. Also you can use the image in the file as the Calibre setting.

In general, resize then compress (by the saving process unless the format is truly loss-less).

[ownedbycats]

When reading multiple books at a time, mixing up the plots and characters and forgetting which book I'm in.

I mostly prevent this by making sure the books I read are different enough from each other but sometimes my brain still gets slippy.

[JSWolf]

Originally Posted by ownedbycats

When reading multiple books at a time, mixing up the plots and characters and forgetting which book I'm in.

I mostly prevent this by making sure the books I read are different enough from each other but sometimes my brain still gets slippy.

On a similar vein, reading a book and then deciding to go for another and not getting back to the first book because you want to finish the second book.