Same Image on save is 10x smaller in size

soyo

Hi.

I would appriciate if someone explained me what I'm doing wrong.

I have a png image, of 256x128 size. It has 8bits per pixel for color. Now this image's size is 97kB. I open it in photoshop, I save it as different png file, and then... this image is 7kB of size.

Can someone tell me what's wrong, or what I'm doing wrong?

Lucas

jerryb4417 · Posted: Sun Mar 11, 2012 5:48 pm Post subject:

hi,
at this point i don't see yet anything wrong , yes there a mystery on different file size... but there a lot possiblities why,,, ie:
1. are you sure the orginal not 24 bit.. changing to 8 bit would definitly reduce files size..

2. also going from 24 to 8 bit that reduction in colors a lot of dithering comes into play...

3. don't know where your reading the 97k, in photoshop or some other program... believe you can get a lot of different readings on the same file... smiling...

4. if this 97k file was made from another program, that program mayhave used different alogrythms tocompress the file if any.. photoshop uses a different alogrythms when it saves png file which maybe give a much smaller file size..

so as you can see there can be a lot of reason why different file size... for the same image... now.. what i am curious why open and resave in the same format while not doing any editing to the image... possibly know the backroung of the workflow can help ....

can you post the orginal and the new one??? maybe tht will five some further clues...

soyo · Posted: Mon Mar 12, 2012 3:41 am Post subject:

Thanks for the reply jerry.

Auieos · Posted: Mon Mar 12, 2012 9:09 pm Post subject:

The first image has a much bigger end of image marker.

Second one has been optimized as Jerry has inferred too.

The number in the length columns add up to the image size in bytes, all the extra size in the first image is caused by the IEND chunk.

soyo · Posted: Tue Mar 13, 2012 1:08 pm Post subject:

Ok guys, thanks a lot for patience. Below is the main cause why I started this topic, but I still can't figure it out. I thought the loss of size is the cause, but you say it's not :/

I'm not that skilled as you guys, so that's the primary reason why I'm here. I will be really gratefull if someone could give me a hint here, or some small help.

To cut to the chase, I'm trying to use a program that creates graphics for older games. This program edits particular files, that have different resolutions and different number of bits per pixel. The problem I have however is the transparency and color palette, as I never had dealings with that. The problem is, that someone created before a pictures that are very smooth, and this seems to be the cause of very smart using of transparency levels, for different colors in the palete. However, I have no idea how to achieve the same effect, I tried many things, but still can't figure this out. I will try to ilustrate the problem below.

Below is a screenshot from this application

On the right is the picture that is the root of my question here. It has to be in the format with palette of collors in amount of 16, although I have no idea where it stores the alpha channel information, as there are 4 bits for color per pixel. Well anyways, you can see on the right top corner the palette. It basicaly has only the shades of gray in this case. I can switch now to the alpha channel mask, and this is what I get:

You can see that each of the colors in the palette has different alpha values. Now what I tried is, I exported the image, I opened it with photoshop, saved it, imported it in the program, and guess what I found in the alpha channel mask:

All the information of the alpha channel for each color is gone!

Here are the examples with more colors(256):

The alpha channel mask

And now, I do the same as before, export it, save it in photoshop, and guess what, all the info is gone again:

Now loosing this information is not a problem, as I will be inputting different pictures, but my question is, how I can achieve the same effect in photoshop for my images that I will try to import. I would love to have as smooth edges as they are seen on those examples above.

Auieos · Posted: Wed Mar 14, 2012 6:26 am Post subject:

This one is tricky because your going back and forth between two different programs so not exactly sure where the issue is happening.

I have a feeling the files are loosing there transparency when they are opened in Photoshop.

If you could upload the smooth version of the soccer ball logo before it has been edited in Photoshop I should be able to tell if this is the case.

Also try saving the image using... File > Save for Web > Preset: PNG-24
That will save smooth edges if they have been successfully transferred into Photoshop from game graphic studio.

domemall · Posted: Tue May 01, 2012 10:22 am Post subject:

thank you

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