Creating transparent PNG with exact RGBA values

Posted by rrowland on Stack Overflow See other posts from Stack Overflow or by rrowland
Published on 2012-10-31T21:15:17Z Indexed on 2012/10/31 23:00 UTC
Read the original article Hit count: 146

Filed under:

compression

|

png

|

photoshop

|

alpha

|

lossless-compression

I'm color-coding a transparent image to be read programatically. However, the image seems to be getting compressed and my code is reading color values other than the ones I mean to pass it.

Concept

Output

This is the output I get, exporting as PNG-24. I programatically check each pixel for one of the six colors I use in creating the image:

0x00000F
0x0000F0
0x000F00
0x00F000
0x0F0000
0xF00000

Each color represents a different texture to apply. Top right (0x00000F) will pull texture from the tile to its top right and blend it at a ratio equal to the opacity of the pixel. The end goal is to create a hex tiled grid with differing textures that blend smoothly.

What's happening

It seems that when converting to PNG, Photoshop will change the RGBA to make it smoother, or just to help compression size. Parts that should be 250 red range anywhere from 150 to 255.

Question

Whether using PNG or another web-compatible format, I need to be able to save these pixel values, essentially instructions, loss-less and still maintain transparency. Is this possible in any format or will I need to re-think my approach?

© Stack Overflow or respective owner

Related posts about compression

Converting linear colors to SRGB shows banding in FFmpeg

as seen on Super User - Search for 'Super User'
When I convert an EXR file sequence with x264 using FFmpeg and convert the colorspace from linear to SRGB (with gamma 0.45454545) I get some heavy banding issues (most visible on a dark gradient). Here is the ffmpeg command I use: C:/ffmpeg.exe -y -i C:/seq_v001.%04d.exr -vf lutrgb=r=gammaval(0… >>> More
IIS7 Compression CSS files only compressed when dynamic compression is enabled

as seen on Server Fault - Search for 'Server Fault'
If anyone can help it would be appreciated. I would like to enable compression for static files within IIS7 (for the sake of simplicity I'll just refer to static css files for the time being). The problem I'm getting is that css files are only compressed when both dynamic and static compression… >>> More
Built-in GZip/Deflate Compression on IIS 7.x

as seen on West-Wind - Search for 'West-Wind'
IIS 7 improves internal compression functionality dramatically making it much easier than previous versions to take advantage of compression that’s built-in to the Web server. IIS 7 also supports dynamic compression which allows automatic compression of content created in your own applications (ASP… >>> More
Domino Document data compression and design compression

as seen on Server Fault - Search for 'Server Fault'
I was thinking of turning this on some large databases not just mail files - we have around 8 - 10GB of large databases as well as small databases of couple of hundred MB in size. But after reading this post I am not too sure: http://www-10.lotus.com/ldd/nd85forum.nsf/4b9931b774db788c85256bf0006b5e6d/1f4e67b569720e54852576c0003cb8ac… >>> More
I need to choose a compression algorithm

as seen on Stack Overflow - Search for 'Stack Overflow'
I need to choose a compression algorithm to compress some data. I don't know the type of data I'll be compressing in advance (think of it as kinda like the WinRAR program). I've heard of the following algorithms but I don't know which one I should use. Can anyone post a short list of pros and cons… >>> More

Related posts about png

Bulk convert PNG-24 to PNG-8 files with best quality

as seen on Super User - Search for 'Super User'
Hi, Can anybody recommend a good method of bulk converting a large amount of PNG-24 files to PNG-8 with as little loss of quality as possible and maintaining transparency? I've tried ImageMagick but the resulting images weren't quite as crisp quality as I'd like. Using Paint.NET I was able to achieve… >>> More
Azure Mobile Services: what files does it consist of?

as seen on ASP.net Weblogs - Search for 'ASP.net Weblogs'
Azure Mobile Services is a platform that provides a small set of functionality consisting of authentication, custom data tables, custom API’s, scheduling scripts and push notifications to be used as the back-end of a mobile application or if you want, any application or web site. As described in my… >>> More
how to rename files with count

as seen on Ask Ubuntu - Search for 'Ask Ubuntu'
i have a directory like this: randomized_quad015.png randomized_quad030.png randomized_quad045.png randomized_quad060.png randomized_quad075.png randomized_quad090.png randomized_quad1005.png randomized_quad1020.png randomized_quad1035.png randomized_quad1050.png randomized_quad105.png randomized_quad1065… >>> More
How can I center XHTML content with CSS?

as seen on Stack Overflow - Search for 'Stack Overflow'
so I recently converted a website of mine from a table content format to a div content format. Table format Version: Table version of the website: here. Table version style CSS: body { width: 1020px; margin: 0 auto; background-image: url(images/bg.png); } .logo{ width:301px; … >>> More
Images in the project NOT adding to array - don't know why.

as seen on Stack Overflow - Search for 'Stack Overflow'
Hi there, I have to sets of images. Each set has 16 images. One set is called 0.png through to 15.png the other is a0.png through to a15.png. In my app, it loads each one dependent on a variable (which by logging, I have proved it works) here is the code [MemoryManager sharedMemoryManager]; NSLog(@"THEME:… >>> More