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Author Topic: [Conversion] Hobbit (Read 9190 times)

Offline IstvanV

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Re: [Conversion] Hobbit
« Reply #15 on: 2017.January.16. 09:59:00 »
unfortunately the pictures remained quite big after compression also, this is the reason why only 4-5 could be loaded into the memory in an EP128

The compressed size could be reduced with less dithering or a different mode (attribute with -palres 1 is the mode that compresses the most poorly). According to Endi, less dithering may also improve the quality, but this probably depends on the image. Another idea is to store the pixel bytes in a different order, at least in the case of Spectrum loading screens they can be compressed better if the image data is in the "C64" (character based) order.

Offline gflorez

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Re: [Conversion] Hobbit
« Reply #16 on: 2017.January.16. 10:15:52 »
Istvanv, and about quality, I think that a light outline of the darker colour zones can improve the  results on some images.

I want to make some tests, but I am not so skilled to draw...

Offline geco

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Re: [Conversion] Hobbit
« Reply #17 on: 2017.January.17. 10:57:53 »
The compressed size could be reduced with less dithering or a different mode (attribute with -palres 1 is the mode that compresses the most poorly). According to Endi, less dithering may also improve the quality, but this probably depends on the image. Another idea is to store the pixel bytes in a different order, at least in the case of Spectrum loading screens they can be compressed better if the image data is in the "C64" (character based) order.
I tried for some pictures mode 3 (col 16 mode), and for best result i did not try -palres 1.
I tested the pictures with different dither settings, most pictures were converted with dither 1 0.4, it was the most fit setting for most pictures, some of them was converted with lower or higher.
EP style format is not better for compression than C64 order? I used continous EP style.

Offline IstvanV

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Re: [Conversion] Hobbit
« Reply #18 on: 2017.January.17. 11:10:35 »
EP style format is not better for compression than C64 order? I used continous EP style.

I did not try the C64 order on IVIEW images yet, but it seems to work better on Spectrum graphics. I noticed in Povi's new Squares game that the loading screen is compressed with some specialized method that reorders the pixel data, and that is how it achieves better efficiency. So, I tried the EP style linear order first which slightly reduced the file size, but the C64 addressing (character cells) gave even better results.

Offline geco

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Re: [Conversion] Hobbit
« Reply #19 on: 2017.January.17. 11:25:13 »
Hm, it is interesting, but I guess it depends on the picture also, how the data is organized on it.
I recognized earlier that compression on CPC and Speccy style is worse than on EP style.

Offline IstvanV

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Re: [Conversion] Hobbit
« Reply #20 on: 2017.January.17. 11:45:37 »
I did a quick test with ARIZONA.RAW packed in C64 format, but it does not make much difference (see original results here):

uncompressed: 55954 bytes (had to be padded because the height was not a multiple of 8 )
-raw -m3 -9: 44523 bytes
-raw -m2 -9: 43110 bytes
-raw -m0 -8: 40875 bytes
-raw -mz -9 -maxoffs 65536: 40763 bytes

So, it is slightly better, but the improvement is minor and it would need additional code to fix the unpacked data. IVIEW images converted from photos or movies just do not compress well and the pixel data is basically random bytes.

Offline IstvanV

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Re: [Conversion] Hobbit
« Reply #21 on: 2017.January.21. 10:34:18 »
Istvanv, and about quality, I think that a light outline of the darker colour zones can improve the  results on some images.

When converting "dark" images, increasing the contrast/gamma may also help, with only 2-3 bits per channel, low contrast images do not look very good on the Enterprise or other 8-bit computers. :)

Offline geco

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Re: [Conversion] Hobbit
« Reply #22 on: 2017.January.21. 21:02:33 »
When converting "dark" images, increasing the contrast/gamma may also help, with only 2-3 bits per channel, low contrast images do not look very good on the Enterprise or other 8-bit computers. :)
I did it, I used GIMP to increase brightness and contrast :) , but probably other thing should be used also, what I did not find, because a lot of pictures was very dark with low contrast.

Offline SlashNet

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Re: [Conversion] Hobbit
« Reply #23 on: 2017.April.04. 20:45:42 »

Offline geco

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Re: [Conversion] Hobbit
« Reply #24 on: 2017.April.05. 08:35:17 »