PNG files in Photoline

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Hangnail
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PNG files in Photoline

Post by Hangnail » Tue 31 May 2005 13:29

Have been working a lot lately with PNG files and have noticed some odd behavior. If I save a file in png format the size remains constant no matter how many colors I reduce it to. In graphic converter the same file size shortens dramatically when you reduce color. If you show save optoins and have it calculate the size you will see it stay the same while the gif estimate changes. Wierd

I'm using OSX 10.4.1

Michael Roek-Ramirez
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Post by Michael Roek-Ramirez » Tue 31 May 2005 15:07

Hi Hangnail:

No problem in my windows version!

Dont you have a file size reduction either when selecting a different Palette or Reduction Method?

Does that happen just in "save as" mode or as well when you select "tool"-"color"-"reduce color"?


Regards

Michael

Hangnail
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Post by Hangnail » Tue 31 May 2005 16:13

Michael Rök-Ramirez wrote:Hi Hangnail:

No problem in my windows version!

Dont you have a file size reduction either when selecting a different Palette or Reduction Method?

Does that happen just in "save as" mode or as well when you select "tool"-"color"-"reduce color"?


Regards

Michael
I've tried it 3 ways with no change in file size.

1. Reduced colors via the tools menu. This looks to be the same dialog box used if you save as and do options for PNG color reduction upon saving. If you bring up an existing PNG and start messing with the colors and have Photoline estimate file size you will notice the gif estimate change while the png estimate stay the same.

2. Reduce colors using save as but it's the same basic dialog box as number 1.

3. change layer type to grayscale via the convert layer type dialog

note that the calculated size matches the file size saved so I don't think its just an issue with the calculation.

If I do the same thing with graphic converter the file size almost halves. I'll keep poking ...

Hangnail
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Post by Hangnail » Tue 31 May 2005 16:21

Additional:

the file size differenc isn't half but it is noticable. 2 meg via photoline and 1.4 via graphic converter. Very strange. Even if I reduce the colors to 2 its still 2 meg

Hangnail
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Post by Hangnail » Tue 31 May 2005 16:27

Additional additional:

Got the file size to reduce but I had to convert the layer type to monochrome. If its 256, grayscale, or higher the file size remains unchanged. Is an alpha channel being saved? i figured taht was the different between an 8bit and 16bit grayscale. I'm using 8bit.

Martin Huber
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Post by Martin Huber » Tue 31 May 2005 16:54

Hangnail wrote:Additional additional:

Got the file size to reduce but I had to convert the layer type to monochrome. If its 256, grayscale, or higher the file size remains unchanged. Is an alpha channel being saved? i figured taht was the different between an 8bit and 16bit grayscale. I'm using 8bit.
I just tried PL32 11.52 on Mac OS X 10.3.5 and I couldn't reproduce this problem.
I did the following:
- I opened an RGB image
- File/Save as...
- Selected "PNG" in the File Format-List
- Pressed "File Size"
- Pressed "Options"
- Activated "Reduce Colors" (which hasn't been activated) and chose a reduction scheme (16 Colors, Best color)
- Left the Options with OK
- Pressed "File Size" and the resulting file size was much smaller

Do you do something different? Does the function "Web/Web Export" work?

Martin

Hangnail
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Post by Hangnail » Tue 31 May 2005 19:22

Ok. Here are the results I started with a 16 million color PNG file

base file is png format and size is: ~5.3 meg

Graphic converter:

256 colors: ~3.7 meg

16 Colors: ~1.8 meg

2 Colors: ~500k

Photoline (using reduce colors on save - nearest color):

256 color: 5.8 meg

16 color: 5.8 meg

2 color 5.8 meg

Photoline (using reduce colors from color tools but not options on save):

Same as above

Photoline (using layer convert functions):

Grayscale: 5.8 meg

black and hite: 800k

Photoline (using web export)

256: 3.7 meg

16: 3.7 meg

2: Not available on web export

I hope I'm doing this right. I am using Tiger but I don't think that could be an issue (I could be wrong of course). I've done this several times to hopefully eliminate proceedural errors but i'm getting consistant behavior. Export seemed to give similar results to Graphic converter in the 256 range.

Martin Huber
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Post by Martin Huber » Tue 31 May 2005 20:31

Hangnail wrote:Photoline (using web export)

256: 3.7 meg

16: 3.7 meg

2: Not available on web export

I hope I'm doing this right. I am using Tiger but I don't think that could be an issue (I could be wrong of course). I've done this several times to hopefully eliminate proceedural errors but i'm getting consistant behavior. Export seemed to give similar results to Graphic converter in the 256 range.
I don't think, the OS version is relevant for this problem.
Because Web Export is the easiest way to export a PNG, we should concentrate on this one. Are there problems with other files, too, or just with this one? If you are changing the number of colors, do you see a corresponding change in the preview? If you are counting the number of colors of the resulting file, do you get the correct number?

Martin

Hangnail
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Post by Hangnail » Wed 01 Jun 2005 03:25

The export seems to be good on the 'calculate' function. All other ways result in a file size the same as the original RGB file. Except when I convert the layer to black and white. Then the normal save function produces output similar to Graphic converter.

I usually work in JPEG and GIF and save work files in native PL32 format so this is the first time I've played with PNG.

Martin Huber
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Post by Martin Huber » Wed 01 Jun 2005 09:05

Hangnail wrote:The export seems to be good on the 'calculate' function.
With "export" you mean the function "Web/Web Export"?
So in Web Export the calculated file sizes are reasonable?
Are the saved files correct, too?
Hangnail wrote:All other ways result in a file size the same as the original RGB file. Except when I convert the layer to black and white. Then the normal save function produces output similar to Graphic converter.
If you reduce the number of colors manually by using "Tool/Color/Reduce Colors...", do you get a correct result? If you use "Tool/Color/Count Colors..." afterwards, do you get the correct number of colors?

Do you have problems just with a single file or is this a common problem?

Did you try a simple RGB image (no transparency, only one layer)?
Hangnail wrote:I usually work in JPEG and GIF and save work files in native PL32 format so this is the first time I've played with PNG.
I don't see any problems on my computer, so it is important, that you answer the questions above. Otherwise it is very hard for me to give you any advice.

Martin

Hangnail
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Post by Hangnail » Wed 01 Jun 2005 23:21

Before I answer I think I found a major clue. The images I've been working with are very high quality scans that are grayscale. However when I open them PL32 (and graphic converter) read the layer as RGB. When I change mode in graphic converter and save it reduces fine and when I use the web/webexport function in PL32 it also reduces fine. Only when I try to reduce colors using the the color reduction dialog box in either the colors tools menu or when I save do I not see any reduction in file size.

Now when I use a PNG image that is 24 bit COLOR to start with the reduction works fine no matter what application and method.

So I wonder if it is something in the file that is either confusing PL32 or a corruption that Graphic converter can deal with. I'll try to upload the file if you want to play but its pretty huge.

Ok use the link below if you want to play with the image I was talking about

http://mysite.verizon.net/hangnail/test/Berserk.png

The color count is about 191 but pl says its an RGB layer. Reducing colors on save won't reduce the file size unless you convert the one layer to black and white. I don't now if there is any hidden transparancy or apha channel. If you use the web/web export function it will reduce to the same size as if you changed mode in graphic converter to gray scale and saved the image normally.

For completeness I'll try to answer the questions you had below:
Martin Huber wrote: With "export" you mean the function "Web/Web Export"?
So in Web Export the calculated file sizes are reasonable?
Are the saved files correct, too?
Yes. Web export worked as I expected and produced an image of the same size as graphic converter did.
Martin Huber wrote:If you reduce the number of colors manually by using "Tool/Color/Reduce Colors...", do you get a c
orrect result? If you use "Tool/Color/Count Colors..." afterwards, do you get the correct number of colors?
This is where I started seeing what probably might be the problem. The scans count around 191 or so colors which is less than 256 shades of grey. Photoline reads it as RGB (so does graphic converter)
Martin Huber wrote:Do you have problems just with a single file or is this a common problem?
Seems to be these files as (mentioned above) I had no issue with a real color 24 bit png.
Martin Huber wrote:Did you try a simple RGB image (no transparency, only one layer)?
Yea ... worked fine.

Sorry for being such a pain. I'm sure I probably am not doing something correctly :oops:

Martin Huber
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Post by Martin Huber » Fri 03 Jun 2005 10:35

Hangnail wrote:Before I answer I think I found a major clue. The images I've been working with are very high quality scans that are grayscale. However when I open them PL32 (and graphic converter) read the layer as RGB. When I change mode in graphic converter and save it reduces fine and when I use the web/webexport function in PL32 it also reduces fine. Only when I try to reduce colors using the the color reduction dialog box in either the colors tools menu or when I save do I not see any reduction in file size.

Now when I use a PNG image that is 24 bit COLOR to start with the reduction works fine no matter what application and method.

So I wonder if it is something in the file that is either confusing PL32 or a corruption that Graphic converter can deal with. I'll try to upload the file if you want to play but its pretty huge.

Ok use the link below if you want to play with the image I was talking about

http://mysite.verizon.net/hangnail/test/Berserk.png

The color count is about 191 but pl says its an RGB layer. Reducing colors on save won't reduce the file size unless you convert the one layer to black and white. I don't now if there is any hidden transparancy or apha channel. If you use the web/web export function it will reduce to the same size as if you changed mode in graphic converter to gray scale and saved the image normally.
I played around with this file quite a while and got the following results:
- the file is opened as RGB layer because it is a palette image
- PL32 11.52 tells me, that the file has 256 colors
- Web Export of PL32 11.52 gives me the following file sizes (all results are median cut, best color):
256 colors: ~1 MByte
64 colors: ~1 MByte
16 colors: ~690 kByte
4 colors: ~320 kByte
The values of 256 and 64 colors are the same, because color reduction in RGB
works with a lower precision in order to reduce memory consumption and to increase speed. This has no negative effects on real photos but does affect RGB images, that are gray images in reality. We will change this in one of the future versions.
- If I use "Save As..." I get the same results with one exception:
256 colors: 1.35 MByte
This is different because the effect described above doesn't happen with "Save As..." because of an internal optimization.

Do you use version 11.52? Previous versions had a bug, that displayed the wrong file size in the "Save As..." under certain circumstances.
Hangnail wrote:Sorry for being such a pain. I'm sure I probably am not doing something correctly :oops:
There is no need to apologize.
This forum exists for asking questions and if there are problems in PL32, we are definitely interested in knowing them.

Martin

Hangnail
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Post by Hangnail » Fri 03 Jun 2005 17:17

I'm using 11.5.2 ... wait ... no im not. jus checked. I downloaded i but guess I didn' install it...


Ok... its official .... I'll go and but my head against the wall now ... :shock:

Martin Huber
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Post by Martin Huber » Mon 06 Jun 2005 19:05

Hangnail wrote:I'm using 11.5.2 ... wait ... no im not. jus checked. I downloaded i but guess I didn' install it...


Ok... its official .... I'll go and but my head against the wall now ... :shock:
At least the mystery is solved :-)

Martin