page.AddPng() does not handle images without a Transparency channel

[cspwcspw]

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Since these are both your packages (thanks) 👍 :

I build a png file using BigGustave and use the byte array to add the image to a pdf. If the PngBuilder Transparency channel is false when I create the png, AddPng seems to get the pixel stride wrong, with interlaced lines, etc. My other tools seem work fine with either png (e.g. file previewer, Paint.Net)

[EliotJones]

I tried a few variations of the image and workflow described but cannot seem to reproduce this. If you're able to share a source.png that causes the issue I'm happy to reopen and take another look but the problem may have been resolved by changes since it was opened? Closing for now.

[cspwcspw]

Thanks Eliot. I should have submitted a proper minimal test case when I submitted the ticket. I've replicated the issue so there is a small command-line program inline here, with the two resulting png images (one generated with and one without the alpha channel), and then the PDF with both images.

using BigGustave;
using System;
using System.IO;
using UglyToad.PdfPig.Content;
using UglyToad.PdfPig.Core;
using UglyToad.PdfPig.Writer;

namespace PngBug
{
    internal class Program
    {
        const string PathPrefix = "C:\\temp\\";   // change this
        const int imgSize = 64;

        static void Main(string[] args)
        {
            File.WriteAllBytes(PathPrefix + "TestPngWithAlpha.png", MakePng(true));
            File.WriteAllBytes(PathPrefix + "TestPngNoAlpha.png", MakePng(false));
          
            // Now write both these into a PDF.  They come out different on my system.  
            File.WriteAllBytes(PathPrefix + "TestPdf.pdf", MakePdf(MakePng(true), MakePng(false)));
        }

        static byte[] MakePdf(byte[] imgWithAlpha, byte[] imgWithoutAlpha)
        {
            PdfDocumentBuilder builder = new PdfDocumentBuilder();
            PdfPageBuilder page = builder.AddPage(PageSize.A4);
            var placementWith = new PdfRectangle(100, 700, 100+imgSize, 700+imgSize);
            page.AddPng(imgWithAlpha, placementWith);
            var placementWithout = new PdfRectangle(300, 700, 300 + imgSize, 700 + imgSize);
            page.AddPng(imgWithoutAlpha, placementWithout);
            byte[] buf = builder.Build();
            return buf;
        }

        public static byte[] MakePng(Boolean useAlphaChannel)
        {
            PngBuilder builder = PngBuilder.Create(imgSize, imgSize, useAlphaChannel);

            for (int r = 0; r < imgSize; r++)
            {
                for (int c = 0; c < imgSize; c++)
                {
                    Pixel px = r < c ? new Pixel(0, 0, 255) : r > c ? new Pixel(255, 0, 0) : new Pixel(0, 0, 0);
                    builder.SetPixel(px, r, c);
                }
            }

            using (var memory = new MemoryStream())
            {
                builder.Save(memory);
                return memory.ToArray();
            }
        }
    }
}

TestPdf.pdf

[EliotJones]

I've had another look with the example you provided, thanks.

It appears the issue was to do with calculation of BitsPerComponent which was fixed here https://github.com/UglyToad/PdfPig/commit/65ff0cb54edbf1f16861bb903faad9652e7a752f#diff-ffb8dc0dfd0b8bc578f2ecd4517965154295f4b8900e71ed5948bc2325dd12ee

Running your sample code with the latest version results in the left file, versus the right hand file which was generated before this fix I assume:

If you can try with the latest pre-release versions the problem should now be fixed.

[cspwcspw]

Thanks Eliot. I confirm this is now fixed.

Kind regards Peter

On Sun, Jun 4, 2023 at 12:35 PM Eliot Jones @.***> wrote:

I've had another look with the example you provided, thanks.

It appears the issue was to do with calculation of BitsPerComponent which was fixed here 65ff0cb #diff-ffb8dc0dfd0b8bc578f2ecd4517965154295f4b8900e71ed5948bc2325dd12ee https://github.com/UglyToad/PdfPig/commit/65ff0cb54edbf1f16861bb903faad9652e7a752f#diff-ffb8dc0dfd0b8bc578f2ecd4517965154295f4b8900e71ed5948bc2325dd12ee

Running your sample code with the latest version results in the left file, versus the right hand file which was generated before this fix I assume:

[image: image] https://user-images.githubusercontent.com/7862346/243171007-76c3efea-826d-44d4-86a2-dee37779234f.png

If you can try with the latest pre-release versions the problem should now be fixed.

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